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CN 11-2282/P
CN 11-2282/P
Volume 47,2021 Issue 1
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2021,47(1):1-10, DOI: 10.7519/j.issn.1000-0526.2021.01.001
Abstract:
This paper shows cloud pictures taken from satellites and aircrafts, trying to link the appearance of the clouds with the three dimensional structure, motion and physical processes that possible exist in the atmosphere by radiative-convective equilibrium theory. In undisturbed atmosphere prevailing horizontal motion， stratus clouds are more or less few and scattered. They spread separately in different layers drifting with the prevailing winds of the layers. On the other hand， deep convection clouds roll in which air flow in different layers are twisted and linked. Although convections happen only in relative small area，they must exist and take important actions in energy balance in the troposphere. The upward energy transportation by convective clouds compensates the heat release by the long wave radiation in the troposphere，and maintains the energy balance in the troposphere.
This paper shows cloud pictures taken from satellites and aircrafts, trying to link the appearance of the clouds with the three dimensional structure, motion and physical processes that possible exist in the atmosphere by radiative-convective equilibrium theory. In undisturbed atmosphere prevailing horizontal motion， stratus clouds are more or less few and scattered. They spread separately in different layers drifting with the prevailing winds of the layers. On the other hand， deep convection clouds roll in which air flow in different layers are twisted and linked. Although convections happen only in relative small area，they must exist and take important actions in energy balance in the troposphere. The upward energy transportation by convective clouds compensates the heat release by the long wave radiation in the troposphere，and maintains the energy balance in the troposphere.
2021,47(1):11-23, DOI: 10.7519/j.issn.1000-0526.2021.01.002
Abstract:
The shortage of long-term satellite radiation products has restricted the study of radiation spatiotemporal variation over the Tibetan Plateau (TP). This paper presents evaluation of the state-of-the-art satellite products called ISCCP-FH （hereinafter to be refered as FH） over the TP. The all-sky OLR, downward shortwave radiation (SWD), upward longwave radiation (LWU) and downward longwave radiation (LWD) during 1984-2017 were compared with observation. The results indicate that the deviations of radiation flux climatology are within 5%, slight error exists in OLR and SWD while large bias is found in LWU. FH radiation fluxes are properly increasing in winter, the trends of OLR and LWD are consistent with observations in all four seasons but LWU weakens falsely. The FH shortwave radiation is generally better than longwave over the TP. The longwave radiation errors can be attributed to that air temperature error would overestimate LWD climatology and trend, and the influence of surface temperature on LWU is opposite. The radiation model, cloud and moisture differences may result in appreciable underestimation of LWD, while the calculation process of FH partly corrects the underestimation of LWU. This study would provide some references for the future use of FH products.
The shortage of long-term satellite radiation products has restricted the study of radiation spatiotemporal variation over the Tibetan Plateau (TP). This paper presents evaluation of the state-of-the-art satellite products called ISCCP-FH （hereinafter to be refered as FH） over the TP. The all-sky OLR, downward shortwave radiation (SWD), upward longwave radiation (LWU) and downward longwave radiation (LWD) during 1984-2017 were compared with observation. The results indicate that the deviations of radiation flux climatology are within 5%, slight error exists in OLR and SWD while large bias is found in LWU. FH radiation fluxes are properly increasing in winter, the trends of OLR and LWD are consistent with observations in all four seasons but LWU weakens falsely. The FH shortwave radiation is generally better than longwave over the TP. The longwave radiation errors can be attributed to that air temperature error would overestimate LWD climatology and trend, and the influence of surface temperature on LWU is opposite. The radiation model, cloud and moisture differences may result in appreciable underestimation of LWD, while the calculation process of FH partly corrects the underestimation of LWU. This study would provide some references for the future use of FH products.
2021,47(1):24-35, DOI: 10.7519/j.issn.1000-0526.2021.01.003
Abstract:
In order to quantitatively analyze the influence of lake on the intensity and properties of precipitation, this paper designes the control experiment and the sensitivity experiment of lake land-surface, based on the mesoscale numerical model of WRF3.8 version and the NCEP/NCAR FNL 1°×1° analysis data with time interval of 6 h. The high value center of heavy precipitation near Poyang Lake from 14 to 15 June 2011 is analyzed. The results show that the surface of Poyang Lake is a “cold source” during the day, which has obvious “cooling” regulation effect on the horizontal range of 100 km and the vertical range of 800 m. This weakening of thermal conditions affects the intensity and durability of the vertical upward motion in the middle and lower troposphere, 〖JP2〗resulting in reduced precipi-〖JP〗tation intensity and shorter precipita-tion duration, which ultimately reduces about 10% of accumulated rainfall near the lake. The underlying surface of Poyang Lake can only improve the saturation degree (relative humidity) of atmospheric water vapor in the boundary layer, but “reduce” the absolute content of water vapor (specific humidity), which is one of the reasons why the sensitivity experiment rather than control experiment precipitation center has greater strength and a wider range of heavy precipitation after lake land-surface. The lower surface of the lake water body results from reducing the atmospheric temperature and absolute humidity of the boundary layer so that the atmosphere has a weaker convection effective potential energy than sensitivity experiment, and the lower atmosphere (1 〖KG-*5〗000-850 hPa) has a weaker convection instability. Sounding reflects the control experiment near the formation has a shallow inverse temperature structure. It has a lower CAPE than the lake terrestrial sensitivity experiment, and finally weakens the convection properties of the control experiment precipitation. Generally speaking, the underlying surface of Poyang Lake changes the temperature and absolute humidity of the boundary layer, thus changing the environmental conditions of the lower atmosphere, and affecting the temperature and humidity conditions of the initial uplift gas block, delaying and weakening the duration and intensity of vertical motion, weakening the convection in the lower layer near the lake, and having a 45% inhibition rate on atmospheric heating, ultimately reducing the intensity and range of precipitation.
In order to quantitatively analyze the influence of lake on the intensity and properties of precipitation, this paper designes the control experiment and the sensitivity experiment of lake land-surface, based on the mesoscale numerical model of WRF3.8 version and the NCEP/NCAR FNL 1°×1° analysis data with time interval of 6 h. The high value center of heavy precipitation near Poyang Lake from 14 to 15 June 2011 is analyzed. The results show that the surface of Poyang Lake is a “cold source” during the day, which has obvious “cooling” regulation effect on the horizontal range of 100 km and the vertical range of 800 m. This weakening of thermal conditions affects the intensity and durability of the vertical upward motion in the middle and lower troposphere, 〖JP2〗resulting in reduced precipi-〖JP〗tation intensity and shorter precipita-tion duration, which ultimately reduces about 10% of accumulated rainfall near the lake. The underlying surface of Poyang Lake can only improve the saturation degree (relative humidity) of atmospheric water vapor in the boundary layer, but “reduce” the absolute content of water vapor (specific humidity), which is one of the reasons why the sensitivity experiment rather than control experiment precipitation center has greater strength and a wider range of heavy precipitation after lake land-surface. The lower surface of the lake water body results from reducing the atmospheric temperature and absolute humidity of the boundary layer so that the atmosphere has a weaker convection effective potential energy than sensitivity experiment, and the lower atmosphere (1 〖KG-*5〗000-850 hPa) has a weaker convection instability. Sounding reflects the control experiment near the formation has a shallow inverse temperature structure. It has a lower CAPE than the lake terrestrial sensitivity experiment, and finally weakens the convection properties of the control experiment precipitation. Generally speaking, the underlying surface of Poyang Lake changes the temperature and absolute humidity of the boundary layer, thus changing the environmental conditions of the lower atmosphere, and affecting the temperature and humidity conditions of the initial uplift gas block, delaying and weakening the duration and intensity of vertical motion, weakening the convection in the lower layer near the lake, and having a 45% inhibition rate on atmospheric heating, ultimately reducing the intensity and range of precipitation.
2021,47(1):36-48, DOI: 10.7519/j.issn.1000-0526.2021.01.004
Abstract:
By using densely-observed snowfall, surface conventional observation, FY-2E satellite TBB and ERA5 reanalysis data, comparative analysis is carried out for two snowfall events with significantly different snow to liquid ratios (SLR) in North China. Based on the analysis of difference of the snowfall characteristics, vertical thermodynamic structure in clouds, verticaldistribution of precipitation particles and surface temperature, the effect of vertical thermodynamic structure and water vapor conditions on snow density is revealed. The results show that the event with higher SLR (hereinafter referred to the 3rd January Case) occurs in a colder condition from surface to upper atmosphere, and the vertical layer with temperature between -18℃ to -12℃ is much thicker, which almost coincides with the level of maximum ascending motion in the cloud. The perfect match of temperature and vertical motion in the cloud leads to the formation of dendritic snowflake and a higher SLR. In addition, the precipitation particles are mainly ice-phase particles in the 3rd January Case. The case with lower SLR (hereinafter referred to the 29th November Case) appears in a warmer condition. The vertical layer with 〖JP2〗temperature between -18℃ to -12℃ is rela-〖JP〗tively thinner, which is located below the level of its maximum ascending motion. This kind of profiles of temperature and vertical motion in the cloud would result in a low SLR snowfall. Besides this, there are large amounts of super-cooled water droplets in the lower level of the cloud, thus the riming process may occur, which would cause a lower SLR further. The 3rd January Case is mainly caused by a short-wave trough, thus its accent motion is relatively weaker with its peak in 〖JP2〗low-level layer. The layer with tempera-〖JP〗ture between -18℃ to -12℃ is located near the frontal zone of a warm front, where there is a strong warm advection and a small temperature lapse rate. This is the main reason why the -18℃ to -12℃ layer for the 3rd January Case is thick. While the 29th November Case is mainly caused by a deep upper trough, which generates a strong updraft with its peak in upper-level layer. The layer with temperature between -18℃ to -12℃ is located over the frontal zone of a cold front, where the temperature lapse rate is much larger, thus -18℃ to -12℃ layer is shallow. Meanwhile, water vapor provided by easterly over boundary layer, which is the primary source for the 3rd January Case, is generally less; while the southwesterly in front of the upper trough brings a plenty of water vapor for the 29th November Case.
By using densely-observed snowfall, surface conventional observation, FY-2E satellite TBB and ERA5 reanalysis data, comparative analysis is carried out for two snowfall events with significantly different snow to liquid ratios (SLR) in North China. Based on the analysis of difference of the snowfall characteristics, vertical thermodynamic structure in clouds, verticaldistribution of precipitation particles and surface temperature, the effect of vertical thermodynamic structure and water vapor conditions on snow density is revealed. The results show that the event with higher SLR (hereinafter referred to the 3rd January Case) occurs in a colder condition from surface to upper atmosphere, and the vertical layer with temperature between -18℃ to -12℃ is much thicker, which almost coincides with the level of maximum ascending motion in the cloud. The perfect match of temperature and vertical motion in the cloud leads to the formation of dendritic snowflake and a higher SLR. In addition, the precipitation particles are mainly ice-phase particles in the 3rd January Case. The case with lower SLR (hereinafter referred to the 29th November Case) appears in a warmer condition. The vertical layer with 〖JP2〗temperature between -18℃ to -12℃ is rela-〖JP〗tively thinner, which is located below the level of its maximum ascending motion. This kind of profiles of temperature and vertical motion in the cloud would result in a low SLR snowfall. Besides this, there are large amounts of super-cooled water droplets in the lower level of the cloud, thus the riming process may occur, which would cause a lower SLR further. The 3rd January Case is mainly caused by a short-wave trough, thus its accent motion is relatively weaker with its peak in 〖JP2〗low-level layer. The layer with tempera-〖JP〗ture between -18℃ to -12℃ is located near the frontal zone of a warm front, where there is a strong warm advection and a small temperature lapse rate. This is the main reason why the -18℃ to -12℃ layer for the 3rd January Case is thick. While the 29th November Case is mainly caused by a deep upper trough, which generates a strong updraft with its peak in upper-level layer. The layer with temperature between -18℃ to -12℃ is located over the frontal zone of a cold front, where the temperature lapse rate is much larger, thus -18℃ to -12℃ layer is shallow. Meanwhile, water vapor provided by easterly over boundary layer, which is the primary source for the 3rd January Case, is generally less; while the southwesterly in front of the upper trough brings a plenty of water vapor for the 29th November Case.
2021,47(1):49-59, DOI: 10.7519/j.issn.1000-0526.2021.01.005
Abstract:
The relationship between the Madden-Julian oscillation (MJO) and the high-latitude wintertime surface air temperature (SAT) is examined based on NCEP-NCAR reanalysis daily data during 1979-2016. The real-time multivariate MJO (RMM) index, which divides the MJO into eight phases, where Phase 2 (Phase 6) corresponds to the enhanced (reduced) convection over the Indian Ocean and Maritime Continent, is used. A significant positive SAT anomaly over northern high-latitude region of (60°-90°N, 180°-60°W) is found 5-15 days following MJO Phase 2, while a negative SAT anomaly appears over the same region about 5-15 days after the MJO is detected in Phase 6, as the tropical forcing changes sign. An analysis of the lagging composite of the geopotential height at 500 hPa indicates that the Arctic SAT anomaly is a result of a north-eastward propagating Rossby wave train associated with the tropical convection anomaly of the MJO, which may have great impacts on intraseasonal SAT variability over high latitude. An analysis of the wave activity flux indicates that the north-eastward propagating Rossby wave train is likely a result of Rossby energy propagation. Composite maps of the specific humidity at 700 hPa also show close relationship with the SAT signals in high latitudes, due to the positive relationship between mid-troposphere specific humidity and downward longwave radiation. These analyses suggest that large-scale circulation anomalies associated with the MJO convection may have great impacts on high-latitude SAT signals, which can result from both advective and radiative processes. Hence, the MJO phases provide useful information for the extended-range forecast of high-latitude surface air temperature during boreal winter.
The relationship between the Madden-Julian oscillation (MJO) and the high-latitude wintertime surface air temperature (SAT) is examined based on NCEP-NCAR reanalysis daily data during 1979-2016. The real-time multivariate MJO (RMM) index, which divides the MJO into eight phases, where Phase 2 (Phase 6) corresponds to the enhanced (reduced) convection over the Indian Ocean and Maritime Continent, is used. A significant positive SAT anomaly over northern high-latitude region of (60°-90°N, 180°-60°W) is found 5-15 days following MJO Phase 2, while a negative SAT anomaly appears over the same region about 5-15 days after the MJO is detected in Phase 6, as the tropical forcing changes sign. An analysis of the lagging composite of the geopotential height at 500 hPa indicates that the Arctic SAT anomaly is a result of a north-eastward propagating Rossby wave train associated with the tropical convection anomaly of the MJO, which may have great impacts on intraseasonal SAT variability over high latitude. An analysis of the wave activity flux indicates that the north-eastward propagating Rossby wave train is likely a result of Rossby energy propagation. Composite maps of the specific humidity at 700 hPa also show close relationship with the SAT signals in high latitudes, due to the positive relationship between mid-troposphere specific humidity and downward longwave radiation. These analyses suggest that large-scale circulation anomalies associated with the MJO convection may have great impacts on high-latitude SAT signals, which can result from both advective and radiative processes. Hence, the MJO phases provide useful information for the extended-range forecast of high-latitude surface air temperature during boreal winter.
2021,47(1):60-70, DOI: 10.7519/j.issn.1000-0526.2021.01.006
Abstract:
In this article, precipitation forecasts from the South China regional hourly updated cycle mesoscale model (GTRAMS-3 km-RUC) are verified based on observations of Fujian Province during May to September in 2017-2018. A correction approach on categorical hourly precipitation forecast using convolutional neural network (CNN) is built and trained, taking into account of issues such as sample imbalance, selection of feature and over-fitting of the system. Comparisons of test between CNN and frequency matching (FM) method on the 2017-2018 test set and the 2019 practical data set are also made for their correction effects. The results show that all these correction methods can improve the original forecast at different degrees, but underperform with precipitation over 15 mm·h-1. CNN performs better than FM, and CNN with correlation coefficient discrimination (CCD) is the most effective for heavy rainfall category. In addition, we apply two different solutions to extract input features of the neural network system. The CNN model converges faster when principal component analysis (PCA) solution is used, but it leads to over-fitting earlier and severely， which implies that the system’s generalization ability needs to be improved further. In contrast, CCD solution displays its longer promotion period and more potential state. It seems that CNN correction method improves forecast ability mainly by reducing the missing ratio for categorical precipitaition forecasts and the false alarm ratio for the rainfall and light rain forecasts.
In this article, precipitation forecasts from the South China regional hourly updated cycle mesoscale model (GTRAMS-3 km-RUC) are verified based on observations of Fujian Province during May to September in 2017-2018. A correction approach on categorical hourly precipitation forecast using convolutional neural network (CNN) is built and trained, taking into account of issues such as sample imbalance, selection of feature and over-fitting of the system. Comparisons of test between CNN and frequency matching (FM) method on the 2017-2018 test set and the 2019 practical data set are also made for their correction effects. The results show that all these correction methods can improve the original forecast at different degrees, but underperform with precipitation over 15 mm·h-1. CNN performs better than FM, and CNN with correlation coefficient discrimination (CCD) is the most effective for heavy rainfall category. In addition, we apply two different solutions to extract input features of the neural network system. The CNN model converges faster when principal component analysis (PCA) solution is used, but it leads to over-fitting earlier and severely， which implies that the system’s generalization ability needs to be improved further. In contrast, CCD solution displays its longer promotion period and more potential state. It seems that CNN correction method improves forecast ability mainly by reducing the missing ratio for categorical precipitaition forecasts and the false alarm ratio for the rainfall and light rain forecasts.
2021,47(1):71-81, DOI: 10.7519/j.issn.1000-0526.2021.01.007
Abstract:
In order to understand the characteristics of particle size distribution during rain and snow processes, ground-based measurements of particle spectrum using a Parsivel disdrometer were compared among samples obtained in 8 rain processes and 10 snow processes in Hohhot from 2017 to 2019. The results show that both the size distributions of raindrop and snowflake are in good agreement with the Gamma distribution. The spectrum width, peak concentration and corresponding diameter of snow spectrum are larger than those of raindrop spectrum, and the snow cases always have larger particle concentration and scale parameters compared to the rain cases when the precipitation intensities are similar. The parameters μ and Λ of Gamma function correspond to the shape and slope of the spectrum, and they satisfy binomial function relationship during both rainfall and snowfall processes, but the fitting effect is poor during snowfall because of the too large-scale range of snowflake. The particle velocity is smaller for snowflake than for raindrop. The falling velocity of raindrops is mostly concentrated at 2-5 m·s-1, while the falling velocity of snowflake is mostly concentrated at 0.5-2 m·s-1, and closer to the speed curve of unfrozen snowflake in comparison.
In order to understand the characteristics of particle size distribution during rain and snow processes, ground-based measurements of particle spectrum using a Parsivel disdrometer were compared among samples obtained in 8 rain processes and 10 snow processes in Hohhot from 2017 to 2019. The results show that both the size distributions of raindrop and snowflake are in good agreement with the Gamma distribution. The spectrum width, peak concentration and corresponding diameter of snow spectrum are larger than those of raindrop spectrum, and the snow cases always have larger particle concentration and scale parameters compared to the rain cases when the precipitation intensities are similar. The parameters μ and Λ of Gamma function correspond to the shape and slope of the spectrum, and they satisfy binomial function relationship during both rainfall and snowfall processes, but the fitting effect is poor during snowfall because of the too large-scale range of snowflake. The particle velocity is smaller for snowflake than for raindrop. The falling velocity of raindrops is mostly concentrated at 2-5 m·s-1, while the falling velocity of snowflake is mostly concentrated at 0.5-2 m·s-1, and closer to the speed curve of unfrozen snowflake in comparison.
2021,47(1):82-93, DOI: 10.7519/j.issn.1000-0526.2021.01.008
Abstract:
Based on the data of three traffic meteorological stations set on Nanjing-Suqian-Xuzhou Expressway observed every ten minutes during 2015-2018, the random forests regression is used to forecast the road surface temperature in the next hour in winter and the feasibility and applicability of the models were analyzed. The results are as follows. The random forests regression method can be used to predict the road surface temperature of the expressway in winter, and the feature input scheme and the parameter debugging are different in different types of traffic meteorological stations. Compared with the simple features, the complex features can replenish and explain the environment and meteorological elements of the traffic meteorological stations better, and they have a higher degree of differentiation between the ordinary road traffic meteorological stations and the traffic meteorological stations near the bridge and water. Thus, the model has a good forecast effect on the general road traffic meteorological stations and the traffic meteorological stations near the water and bridges, but a little poor forecast effect on the traffic meteorological stations in the service areas. The reduction of the average error rate out of bag does not mean the improvement of the prediction accuracy. The random forest regression model simulated from the complex features can be used to predict the road surface temperature of different types of traffic weather stations in winter no matter in what weather conditions. The forecast effect is the best in rainy and snowy days, followed by in ouvercast days, but slightly worse in sunny days.
Based on the data of three traffic meteorological stations set on Nanjing-Suqian-Xuzhou Expressway observed every ten minutes during 2015-2018, the random forests regression is used to forecast the road surface temperature in the next hour in winter and the feasibility and applicability of the models were analyzed. The results are as follows. The random forests regression method can be used to predict the road surface temperature of the expressway in winter, and the feature input scheme and the parameter debugging are different in different types of traffic meteorological stations. Compared with the simple features, the complex features can replenish and explain the environment and meteorological elements of the traffic meteorological stations better, and they have a higher degree of differentiation between the ordinary road traffic meteorological stations and the traffic meteorological stations near the bridge and water. Thus, the model has a good forecast effect on the general road traffic meteorological stations and the traffic meteorological stations near the water and bridges, but a little poor forecast effect on the traffic meteorological stations in the service areas. The reduction of the average error rate out of bag does not mean the improvement of the prediction accuracy. The random forest regression model simulated from the complex features can be used to predict the road surface temperature of different types of traffic weather stations in winter no matter in what weather conditions. The forecast effect is the best in rainy and snowy days, followed by in ouvercast days, but slightly worse in sunny days.
2021,47(1):94-105, DOI: 10.7519/j.issn.1000-0526.2021.01.009
Abstract:
Based on the observation data from agrometeorological stations from 1981 to 2016 in Heilongjiang Province， the indicators of water deficiency index (KCWDI) and accumulated temperature anomaly ≥10℃（H） from the People’s Republic of China meteorological industry standards， this paper assesses the drought and cold damage to maize during emergence-milk ripening stage separately, and stipulates the drought and cold damage cross-stress occurs at the same station in the same year. Besides, the temporal and spatial distribution characteristics of it are analyzed. The relational model between KCWDI, H and maize yield is constructed by mathematical statistical method, and the effects of single drought， single cold damage or drought and cold damage cross-stress on maize yield are investigated by comparative method. The results show that the changes of KCWDI and H are consistent with the spatial distribution of water resources and climate warming trend in the study area. During the analysis period, the sum of years of drought was 242 station years, and the sum of years of cold damage was 76 station years, while the sum of years of drought and cold damage cross-stress was 91 station years during maize emergence-milk ripening stage in the study area. The occurrence of drought and cold damage cross-stress presents a decreasing trend, and its appearance was high before mid-1990. After that, the frequency got to decline. The occurrence of drought and cold damage cross-stress in the west is higher than that in the east, and there is frequent drought and cold damage cross-stress in Songnen Plain. Correlation amid H, KCWDI and maize yield is significant (P＜0.05 or P＜0.01） in maize emergence-milk ripening stage. In a certain range of temperature and water condition, H decreases and KCWDI increases, which is unfavorable for the increase of maize yield. On the contrary，increasing temperature and decreasing water deficit is advantageous to maize yield increase. In general, there exists a trend that the more severe the degree of single drought, single cold damage or drought and cold damage cross-stress is, the lower the yield would be. Comparing the effects of the single drought (single cold damage), and combined occurrence of drought and cold damage on maize yield shows that when the time, days and degree of the single drought (cold damage) is equivalent to drought (cold damage) in combined occurrence of drought and cold damage, then the drought is superimposed with cold damage (drought), which means the trend of its disadvantageous effect on maize yield is increasing.
Based on the observation data from agrometeorological stations from 1981 to 2016 in Heilongjiang Province， the indicators of water deficiency index (KCWDI) and accumulated temperature anomaly ≥10℃（H） from the People’s Republic of China meteorological industry standards， this paper assesses the drought and cold damage to maize during emergence-milk ripening stage separately, and stipulates the drought and cold damage cross-stress occurs at the same station in the same year. Besides, the temporal and spatial distribution characteristics of it are analyzed. The relational model between KCWDI, H and maize yield is constructed by mathematical statistical method, and the effects of single drought， single cold damage or drought and cold damage cross-stress on maize yield are investigated by comparative method. The results show that the changes of KCWDI and H are consistent with the spatial distribution of water resources and climate warming trend in the study area. During the analysis period, the sum of years of drought was 242 station years, and the sum of years of cold damage was 76 station years, while the sum of years of drought and cold damage cross-stress was 91 station years during maize emergence-milk ripening stage in the study area. The occurrence of drought and cold damage cross-stress presents a decreasing trend, and its appearance was high before mid-1990. After that, the frequency got to decline. The occurrence of drought and cold damage cross-stress in the west is higher than that in the east, and there is frequent drought and cold damage cross-stress in Songnen Plain. Correlation amid H, KCWDI and maize yield is significant (P＜0.05 or P＜0.01） in maize emergence-milk ripening stage. In a certain range of temperature and water condition, H decreases and KCWDI increases, which is unfavorable for the increase of maize yield. On the contrary，increasing temperature and decreasing water deficit is advantageous to maize yield increase. In general, there exists a trend that the more severe the degree of single drought, single cold damage or drought and cold damage cross-stress is, the lower the yield would be. Comparing the effects of the single drought (single cold damage), and combined occurrence of drought and cold damage on maize yield shows that when the time, days and degree of the single drought (cold damage) is equivalent to drought (cold damage) in combined occurrence of drought and cold damage, then the drought is superimposed with cold damage (drought), which means the trend of its disadvantageous effect on maize yield is increasing.
2021,47(1):106-116, DOI: 10.7519/j.issn.1000-0526.2021.01.010
Abstract:
Ewiniar (1804), a tropical storm with weak tropical cyclone (TC) intensity but strong and long lasting precipitation, is taken as the research object in this study. By using the conventional and unconventional observations, and NCEP analysis data, the causes of persistent heavy rainfall of the “weak” TC are analyzed. Ewiniar moved very slowly due to the very weak steering flow caused by the large scale circulation background. As a result, its TC circulation maintained for a long time over the offshore waters in South China. Water vapor and momentum were transported to the TC circulation continuously by both the abnormal strong southwest jet induced by the onset of the South China monsoon and the easterly jet caused by Maliksi (1805). Diagnosis of net water vapor budget shows that in the early stage, water vapor inflow mainly came from Ewiniar’s southern boundary, and then water inflow in the eastern boundary increased rapidly, which played an important role in maintaining the continuous water input in the whole TC circulation. As a result, the water flux convergence and high humidity and high energy environment along the coastal areas of Guangdong maintained. Strong southeast onshore wind existed for a long spell along the coastal areas of Guangdong. Impacted by the costal line and topography, sustained convergence can be found in lower-level along coastal areas, which could provide favorable dynamic conditions for the continuous generation of heavy rainfall and triggering of mesoscale convective system. And the enhancement of the southeast wind speed in lower troposphere was in good agreement with the sharp increase in precipitation. There were active mesoscale convective systems along the coastal areas, accompanying the occurrence and development of five-stage mesoscale convective rain belts. The continuous generation of new convections in the coastal areas, the development of mesoscale spiral rain band, the superposition of TC inner core precipitation and convections in the outer rain belt, as well as the migration of convection over sea from the two warm wet conveyor belts all contributed to the persistence of the mesoscale convective system in the coastal area of Guangdong Province, resulting in the generation of persistent heavy rainfall there.
Ewiniar (1804), a tropical storm with weak tropical cyclone (TC) intensity but strong and long lasting precipitation, is taken as the research object in this study. By using the conventional and unconventional observations, and NCEP analysis data, the causes of persistent heavy rainfall of the “weak” TC are analyzed. Ewiniar moved very slowly due to the very weak steering flow caused by the large scale circulation background. As a result, its TC circulation maintained for a long time over the offshore waters in South China. Water vapor and momentum were transported to the TC circulation continuously by both the abnormal strong southwest jet induced by the onset of the South China monsoon and the easterly jet caused by Maliksi (1805). Diagnosis of net water vapor budget shows that in the early stage, water vapor inflow mainly came from Ewiniar’s southern boundary, and then water inflow in the eastern boundary increased rapidly, which played an important role in maintaining the continuous water input in the whole TC circulation. As a result, the water flux convergence and high humidity and high energy environment along the coastal areas of Guangdong maintained. Strong southeast onshore wind existed for a long spell along the coastal areas of Guangdong. Impacted by the costal line and topography, sustained convergence can be found in lower-level along coastal areas, which could provide favorable dynamic conditions for the continuous generation of heavy rainfall and triggering of mesoscale convective system. And the enhancement of the southeast wind speed in lower troposphere was in good agreement with the sharp increase in precipitation. There were active mesoscale convective systems along the coastal areas, accompanying the occurrence and development of five-stage mesoscale convective rain belts. The continuous generation of new convections in the coastal areas, the development of mesoscale spiral rain band, the superposition of TC inner core precipitation and convections in the outer rain belt, as well as the migration of convection over sea from the two warm wet conveyor belts all contributed to the persistence of the mesoscale convective system in the coastal area of Guangdong Province, resulting in the generation of persistent heavy rainfall there.
2021,47(1):117-126, DOI: 10.7519/j.issn.1000-0526.2021.01.011
Abstract:
In the summer of 2020, the weather and climate in China were extremely abnormal. The national average precipitation was 373.0 mm, with 14.7% more than normal, which is the second most since 1961. The intraseasonal variation of summer rainfall was obvious. The rainbelt from June to July was mainly located in the Yangtze-Huaihe River Valley (YHRV), but moved northward to Northeast China, North China, and Southwest China in August, making the distribution of summer rainfall in 2020 not belong to any of the four traditional patterns of rainfall. The observational analysis on atmospheric circulation and sea surface temperature indicates that the atmospheric circulation in the mid-high latitude was characterized by “two ridges and one trough” over Eurasia from June to July. The East Asian summer monsoon (EASM) was very weak, and the western Pacific subtropical high (WPSH) was much stronger and further westward than normal. The meridional movement of WPSH presented the characteristics of quasi-biweekly oscillation, accompanied with the early first northward jump and delayed second northward jump, which makes the intensified water vapor transport from the tropical Northwest Pacific. Combined with the cold air activities going southward from the mid-high latitude, the abnormal moisture convergence was located over the middle and lower reaches of the Yangtze River, which leads to excessive Meiyu rainfall in YHRV. The persistent Indian Ocean basin-wide warming played an important role in maintaining the stronger WPSH and weaker EASM than normal during June-July. By contrast, the atmospheric circulation in mid-high latitude was adjusted to “two troughs and one ridge” over Eurasia in August, with a low trough near Mongolia; the WPSH changed from the East-West zonal distribution to the “block” pattern, located further northward. The abnormal southwesterly moisture transport along the edge of WPSH extended to North-Northeast China, forming an abnormal “northeast-southwest” rainbelt, which is obviously different from that during June-July. The abnormal activity of the tropical Madden-Julian Oscillation was an important factor for the adjustment of the atmospheric circulation in mid-low latitude in August 2020.
In the summer of 2020, the weather and climate in China were extremely abnormal. The national average precipitation was 373.0 mm, with 14.7% more than normal, which is the second most since 1961. The intraseasonal variation of summer rainfall was obvious. The rainbelt from June to July was mainly located in the Yangtze-Huaihe River Valley (YHRV), but moved northward to Northeast China, North China, and Southwest China in August, making the distribution of summer rainfall in 2020 not belong to any of the four traditional patterns of rainfall. The observational analysis on atmospheric circulation and sea surface temperature indicates that the atmospheric circulation in the mid-high latitude was characterized by “two ridges and one trough” over Eurasia from June to July. The East Asian summer monsoon (EASM) was very weak, and the western Pacific subtropical high (WPSH) was much stronger and further westward than normal. The meridional movement of WPSH presented the characteristics of quasi-biweekly oscillation, accompanied with the early first northward jump and delayed second northward jump, which makes the intensified water vapor transport from the tropical Northwest Pacific. Combined with the cold air activities going southward from the mid-high latitude, the abnormal moisture convergence was located over the middle and lower reaches of the Yangtze River, which leads to excessive Meiyu rainfall in YHRV. The persistent Indian Ocean basin-wide warming played an important role in maintaining the stronger WPSH and weaker EASM than normal during June-July. By contrast, the atmospheric circulation in mid-high latitude was adjusted to “two troughs and one ridge” over Eurasia in August, with a low trough near Mongolia; the WPSH changed from the East-West zonal distribution to the “block” pattern, located further northward. The abnormal southwesterly moisture transport along the edge of WPSH extended to North-Northeast China, forming an abnormal “northeast-southwest” rainbelt, which is obviously different from that during June-July. The abnormal activity of the tropical Madden-Julian Oscillation was an important factor for the adjustment of the atmospheric circulation in mid-low latitude in August 2020.
2021,47(1):127-132, DOI: 10.7519/j.issn.1000-0526.2021.01.012
Abstract:
The main characteristics of the general atmospheric circulation over the Northern Hemisphere in October 2020 are as follows. The polar vortex showed a dipole pattern with intensity similar to climatic state. The western Pacific subtropical high broke into two rings near 130°E. As a whole, the subtropical high was stronger than normal, and the location of its east ring was noticeably more eastward and northward than normal. During the month, the subtropical high experienced weakening with retreating to the east and then moving westward again. The October monthly mean precipitation in China was 30.1 mm, less than the normal by 16%. The monthly average temperature of China was 10.4℃, roughly equivalent to climatic state. There were four nationwide cold air processes with moderate strengths in this month, of which the strong cold air event during 20-23 caused blowing sand. Two torrential rain processes occurred in October, one was triggered by shear line with cold air and the other by typhoon. There were seven typhoons generated in the western North Pacific and the South China Sea in this month, 3.3 more than average numbers. One of the seven typhoons made a landfall. In addition, one haze-fog process was seen in October, and the autumn rainfall in western China was more than normal, lasting a longer time.
The main characteristics of the general atmospheric circulation over the Northern Hemisphere in October 2020 are as follows. The polar vortex showed a dipole pattern with intensity similar to climatic state. The western Pacific subtropical high broke into two rings near 130°E. As a whole, the subtropical high was stronger than normal, and the location of its east ring was noticeably more eastward and northward than normal. During the month, the subtropical high experienced weakening with retreating to the east and then moving westward again. The October monthly mean precipitation in China was 30.1 mm, less than the normal by 16%. The monthly average temperature of China was 10.4℃, roughly equivalent to climatic state. There were four nationwide cold air processes with moderate strengths in this month, of which the strong cold air event during 20-23 caused blowing sand. Two torrential rain processes occurred in October, one was triggered by shear line with cold air and the other by typhoon. There were seven typhoons generated in the western North Pacific and the South China Sea in this month, 3.3 more than average numbers. One of the seven typhoons made a landfall. In addition, one haze-fog process was seen in October, and the autumn rainfall in western China was more than normal, lasting a longer time.
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Abstract：Abstract:The warm-sector rainstorms over the Sichuan Basin are defined,and classified into four types based on the synoptic situation,including the southwest vortex (SWV),the edge of subtropical high (ESH),the southwest jet (SWJ), and the southeast wind (SEW) types.By using the conventional and the hourly precipitation data of automatic weather station from May to September during 2008-2018,we statistically analyzed the temporal-spatial distribution of warm-sector rainstorms and the nature of precipitation as well as the mesoscale characteristics and causes for their formation. The major characteristics obtained from the research are:(1)The four types usually occur in windward slope mountain,bellmouth topography and near the uneven surface which is transitional zones between plain, hills and uplands,etc. The SWV and SWJ types have a large area,and the former mainly occurs in the middle and south of the basin,the latter from the middle of the basin to the north of Longmen Mountains and Daba Mountains.The ESH and SEW types are decentralized precipitation,and the precipitation usually occur in the west of the basin.(2)All the four types of precipitation have substantial diurnal variation,showing a single peak type,which is strengthened at night and weakened during the day.(3)The warm-sector rainstorms consist of steady and convective precipitation. The heavier the daily rainfall is,the more obvious convective nature the precipitation is of.Among them,the convective precipitation of subtropical high edge and southeast wind type is obvious,and the steady precipitation of southwest vortex and southwest jet type is obvious.（4）The warm-sector rainstorms are directly caused by the development of MβCSs,which the lives of southwest vortex and southwest jet type are ≥6hrs,and those of subtropical high edge and southeast wind type are ≤6hrs. All the four types convective precipitation(20-50 mm·h-1)lasts for no more than 3hrs,and the flash heavy rain(≥50mm·h-1)lasts for no more than 1h,it is easy to cause extreme precipitation events,southwest vortex and southwest jet type are prone to extreme heavy rainfall. (5)The four types occur in the unstable environment with high energy and high humidity. The average CAPE value is more than 1000 J · kg-1, K index is about 40 ℃, θse of 850hPa is about 85 ℃, and the average specific humidity can reach 16 g · kg-1。
Abstract：Abstract:The warm-sector rainstorms over the Sichuan Basin are defined,and classified into four types based on the synoptic situation,including the southwest vortex (SWV),the edge of subtropical high (ESH),the southwest jet (SWJ), and the southeast wind (SEW) types.By using the conventional and the hourly precipitation data of automatic weather station from May to September during 2008-2018,we statistically analyzed the temporal-spatial distribution of warm-sector rainstorms and the nature of precipitation as well as the mesoscale characteristics and causes for their formation. The major characteristics obtained from the research are:(1)The four types usually occur in windward slope mountain,bellmouth topography and near the uneven surface which is transitional zones between plain, hills and uplands,etc. The SWV and SWJ types have a large area,and the former mainly occurs in the middle and south of the basin,the latter from the middle of the basin to the north of Longmen Mountains and Daba Mountains.The ESH and SEW types are decentralized precipitation,and the precipitation usually occur in the west of the basin.(2)All the four types of precipitation have substantial diurnal variation,showing a single peak type,which is strengthened at night and weakened during the day.(3)The warm-sector rainstorms consist of steady and convective precipitation. The heavier the daily rainfall is,the more obvious convective nature the precipitation is of.Among them,the convective precipitation of subtropical high edge and southeast wind type is obvious,and the steady precipitation of southwest vortex and southwest jet type is obvious.（4）The warm-sector rainstorms are directly caused by the development of MβCSs,which the lives of southwest vortex and southwest jet type are ≥6hrs,and those of subtropical high edge and southeast wind type are ≤6hrs. All the four types convective precipitation(20-50 mm·h-1)lasts for no more than 3hrs,and the flash heavy rain(≥50mm·h-1)lasts for no more than 1h,it is easy to cause extreme precipitation events,southwest vortex and southwest jet type are prone to extreme heavy rainfall. (5)The four types occur in the unstable environment with high energy and high humidity. The average CAPE value is more than 1000 J · kg-1, K index is about 40 ℃, θse of 850hPa is about 85 ℃, and the average specific humidity can reach 16 g · kg-1。
Abstract:
On March 21, 2019, a hail process caused by long-lived supercell, occurred in Zhejiang Province. In order to study the environmental background and microphysical characteristics of supercell which maintained for a long time, it is analyzed by using conventional data, Ningbo S-band dual polarization radar data and hydrometeor classification algorithm. The results show that: the trough, 850hPa shear line and the surface cold front provided the suitable background for the supercell. The increase of convective instability in the storm propagation area, high speed of storm bearing layer, the similarity of the mean wind direction of the storm bearing layer and moving direction of the storm, as well as the surface energy front, and the increase of rotation speed and thickness of mesocyclone produced by the enhancement of strong vertical wind shear in the coastal area, which maked the convective storm maintain for a long time. Through the analysis of the structure of the hailstorm, the vigorous convection (the maximum reflectivity above 60dBZ, the storm top above 8km) was found in the whole life cycle, and three obvious fluctuations of height of storm centroid appeared, corresponding to three hail processes. In this case the vertical integrated liquid water content (VIL) jump increment was less than the traditional index, but the combination of the vertical integrated liquid water content density (VILD), the max VIL and the maximum reflectivity factor could still indicate the hailstorm. Through the analysis of the dual polarization characteristics, it is found that the tumbling of falling hail resulted in the Zdr close to 0dB, difference of horizontal and vertical polarization wave leaded to the appearance of large Zdr region at the root of TBSS, and the water coated phenomenon maked it increase and CC value decrease; the polarization parameters Zdr and CC could be used to identify hail in high altitude; Zdr column, near BWER, could not only indicate the ascending motion, but also reveal the different growth stages of hail monomer.
On March 21, 2019, a hail process caused by long-lived supercell, occurred in Zhejiang Province. In order to study the environmental background and microphysical characteristics of supercell which maintained for a long time, it is analyzed by using conventional data, Ningbo S-band dual polarization radar data and hydrometeor classification algorithm. The results show that: the trough, 850hPa shear line and the surface cold front provided the suitable background for the supercell. The increase of convective instability in the storm propagation area, high speed of storm bearing layer, the similarity of the mean wind direction of the storm bearing layer and moving direction of the storm, as well as the surface energy front, and the increase of rotation speed and thickness of mesocyclone produced by the enhancement of strong vertical wind shear in the coastal area, which maked the convective storm maintain for a long time. Through the analysis of the structure of the hailstorm, the vigorous convection (the maximum reflectivity above 60dBZ, the storm top above 8km) was found in the whole life cycle, and three obvious fluctuations of height of storm centroid appeared, corresponding to three hail processes. In this case the vertical integrated liquid water content (VIL) jump increment was less than the traditional index, but the combination of the vertical integrated liquid water content density (VILD), the max VIL and the maximum reflectivity factor could still indicate the hailstorm. Through the analysis of the dual polarization characteristics, it is found that the tumbling of falling hail resulted in the Zdr close to 0dB, difference of horizontal and vertical polarization wave leaded to the appearance of large Zdr region at the root of TBSS, and the water coated phenomenon maked it increase and CC value decrease; the polarization parameters Zdr and CC could be used to identify hail in high altitude; Zdr column, near BWER, could not only indicate the ascending motion, but also reveal the different growth stages of hail monomer.
Abstract:
Recently, the theory of machine learning, as well as its applications in severe convective weather, has been developed in an unprecedented speed. Various machine learning algorithms, such as random forest, decision tree, support vector machine, neural network and deep learning have played important roles in severe convective weather monitoring, nowcasting, short-term forecasting and short-range forecasting, which often got better performances than traditional methods. With the help of machine learning, it is easier to extract the meso-scale features of convective systems in high temporal and spatial resolution observation data, resulting in better performances of automatic convective weather identification and tracking and warning. Machine learning is also a good tool for multi-source data integration, including observation data integration and observation and numerical weather prediction(NWP) data integration. Machine learning can also be an effective postprocessing method for NWP. Many works have showed that machine learning can extract the features of severe weather happening from global or regional NWP data and give a reliable severe weather forecasts. Finally, the issues and outlooks of machine learning application are presented.
Recently, the theory of machine learning, as well as its applications in severe convective weather, has been developed in an unprecedented speed. Various machine learning algorithms, such as random forest, decision tree, support vector machine, neural network and deep learning have played important roles in severe convective weather monitoring, nowcasting, short-term forecasting and short-range forecasting, which often got better performances than traditional methods. With the help of machine learning, it is easier to extract the meso-scale features of convective systems in high temporal and spatial resolution observation data, resulting in better performances of automatic convective weather identification and tracking and warning. Machine learning is also a good tool for multi-source data integration, including observation data integration and observation and numerical weather prediction(NWP) data integration. Machine learning can also be an effective postprocessing method for NWP. Many works have showed that machine learning can extract the features of severe weather happening from global or regional NWP data and give a reliable severe weather forecasts. Finally, the issues and outlooks of machine learning application are presented.
Abstract:
In August 2019, the GLC-12A-type mobile X-band dual-polarization weather radar, which developed by Fourteen Research Institute of China Electronics Technology Group, was conducted field tests in Dafeng, Jiangsu Province. In this paper, the data quality of the Mobile X-band dual-polarization radar is analyzed by using the field observation data of this radar, CINRAD/SA radar in Yancheng , and the data of six rainfall stations in Jiangsu Province. The results show that in the range of 0-30km, the x-band dual-polarizationo weather radar attenuates only in the high reflectivity value, but seriously outside 30km. In order to reduce the observation error caused by attenuation, the difference reflectivity Zdr and Correlation Coefficient ρhv(0) are corrected by signal-to-noise ratio (SNR) to improve the data quality for ground or biological clutter removing. Then the Kdp or φdp after quality control is used to express the total bidirectional reflectivity factor attenuation correction at the distance of R(km) in rain. In last, The paper shows that the data quality of the revised Mobile x-band dual polarization radar is improved.
In August 2019, the GLC-12A-type mobile X-band dual-polarization weather radar, which developed by Fourteen Research Institute of China Electronics Technology Group, was conducted field tests in Dafeng, Jiangsu Province. In this paper, the data quality of the Mobile X-band dual-polarization radar is analyzed by using the field observation data of this radar, CINRAD/SA radar in Yancheng , and the data of six rainfall stations in Jiangsu Province. The results show that in the range of 0-30km, the x-band dual-polarizationo weather radar attenuates only in the high reflectivity value, but seriously outside 30km. In order to reduce the observation error caused by attenuation, the difference reflectivity Zdr and Correlation Coefficient ρhv(0) are corrected by signal-to-noise ratio (SNR) to improve the data quality for ground or biological clutter removing. Then the Kdp or φdp after quality control is used to express the total bidirectional reflectivity factor attenuation correction at the distance of R(km) in rain. In last, The paper shows that the data quality of the revised Mobile x-band dual polarization radar is improved.
Abstract:
Based on the observation data of 360 ° occlusion elevation angle and cloud amount around the observation site, the influence of occlusion on the consistency of sunshine observation data is analyzed. From the relative relationship between the solarSelevationSangleSand the occlusion elevation angle, and the correction of the cloud to the occlusion rate, the correction method of the occlusion sunshine hours by station under cloudy weather conditions was established. Taking Wushan station in Chongqing as an example, the calculation and correction of the sunshine hours during the period of severe occlusion from 2004 to 2013 were performed. Through the vertical comparison between the occlusion period and the two unoccluded periods before and after, and the same period horizontal comparison of Jianshi station in Hubei Province, which is similar to the terrain and climate conditions, the correction effect is tested. The results show that: The obstructions around the observation site of Wushan Station affect the observation of the hours of sunshine, which makes the observation data inconsistent before and after; During the period of 2004-2013, the average number of sunshine hours blocked was 218.0 h/a, and the blocking ratio reached 13.1%. Due to the hedging effect of weather conditions, the influence of blocked in summer half year may be higher than that in winter half year; From the indirect comparison between the vertical and horizontal aspects, the correction method established in this paper not only calculates the influence of the occluder itself, but also takes into account the correction of the occlusion ration under cloudy conditions. The correction results are basically reasonable, and can be relatively accurately restore the occluded sunshine hours.
Based on the observation data of 360 ° occlusion elevation angle and cloud amount around the observation site, the influence of occlusion on the consistency of sunshine observation data is analyzed. From the relative relationship between the solarSelevationSangleSand the occlusion elevation angle, and the correction of the cloud to the occlusion rate, the correction method of the occlusion sunshine hours by station under cloudy weather conditions was established. Taking Wushan station in Chongqing as an example, the calculation and correction of the sunshine hours during the period of severe occlusion from 2004 to 2013 were performed. Through the vertical comparison between the occlusion period and the two unoccluded periods before and after, and the same period horizontal comparison of Jianshi station in Hubei Province, which is similar to the terrain and climate conditions, the correction effect is tested. The results show that: The obstructions around the observation site of Wushan Station affect the observation of the hours of sunshine, which makes the observation data inconsistent before and after; During the period of 2004-2013, the average number of sunshine hours blocked was 218.0 h/a, and the blocking ratio reached 13.1%. Due to the hedging effect of weather conditions, the influence of blocked in summer half year may be higher than that in winter half year; From the indirect comparison between the vertical and horizontal aspects, the correction method established in this paper not only calculates the influence of the occluder itself, but also takes into account the correction of the occlusion ration under cloudy conditions. The correction results are basically reasonable, and can be relatively accurately restore the occluded sunshine hours.
Abstract:
By virtue of the daily temperature observations of 2400 stations in China from 1960 to 2019, the climatological characteristics of the cold event in China are systematically analyzed, and the relationship between cold wave, cold air process and the Arctic Oscillation (AO) is discussed. The results show that the cold wave and cold air process in China mainly occur in autumn, winter and spring, and the frequency and intensity have obvious monthly and seasonal differences. Regional cold wave has the highest frequency in autumn, and national cold wave and all types of cold air have the highest frequency in winter. The average intensity of regional cold event is the largest in February, and the average intensity of national cold event is the largest in November. Based on the analysis of winter temperature in China, the past 60 years can be divided into two stages, that is, the cold period from 1960 to 1986 and the warm period from 1987 to 2019. In the winter of cold period, the frequency of the national cold wave shows a significant decrease trend (-0.57 times/10 years), and the frequency of regional cold air and all-type (the sum of national type and regional type) cold air processes in winter shows a significant upward trend of 1.37 times/10 years and 1.28 times/10 years, respectively. In the warm period, there is a significantly decreasing trend of national cold wave frequency (-0.17 times/10 years) and a significantly increasing trend of regional cold air frequency (0.53 times/10 years) in January. The frequency and intensity of cold wave and cold air over China are closely related to the Arctic Oscillation (AO). On the interannual scale, the frequency (intensity) of various cold wave in various seasons is negatively correlated with the AO index, but the frequency (intensity) of various cold air in winter is positively correlated with AO index. On the interdecadal scale, the frequency of winter regional cold wave, the frequency of national cold wave, and the intensity of national cold wave are significantly positively correlated with the AO index.
By virtue of the daily temperature observations of 2400 stations in China from 1960 to 2019, the climatological characteristics of the cold event in China are systematically analyzed, and the relationship between cold wave, cold air process and the Arctic Oscillation (AO) is discussed. The results show that the cold wave and cold air process in China mainly occur in autumn, winter and spring, and the frequency and intensity have obvious monthly and seasonal differences. Regional cold wave has the highest frequency in autumn, and national cold wave and all types of cold air have the highest frequency in winter. The average intensity of regional cold event is the largest in February, and the average intensity of national cold event is the largest in November. Based on the analysis of winter temperature in China, the past 60 years can be divided into two stages, that is, the cold period from 1960 to 1986 and the warm period from 1987 to 2019. In the winter of cold period, the frequency of the national cold wave shows a significant decrease trend (-0.57 times/10 years), and the frequency of regional cold air and all-type (the sum of national type and regional type) cold air processes in winter shows a significant upward trend of 1.37 times/10 years and 1.28 times/10 years, respectively. In the warm period, there is a significantly decreasing trend of national cold wave frequency (-0.17 times/10 years) and a significantly increasing trend of regional cold air frequency (0.53 times/10 years) in January. The frequency and intensity of cold wave and cold air over China are closely related to the Arctic Oscillation (AO). On the interannual scale, the frequency (intensity) of various cold wave in various seasons is negatively correlated with the AO index, but the frequency (intensity) of various cold air in winter is positively correlated with AO index. On the interdecadal scale, the frequency of winter regional cold wave, the frequency of national cold wave, and the intensity of national cold wave are significantly positively correlated with the AO index.
Abstract:
In order to do well artificial rainfall mitigation on specific target period and area, cloud seeding condition such as cloud properties and structure, moving speed and direction, cloud evolution, precipitation mechanism and so on was forecast by using Cloud Precipitation Explicit Forecast System (CPEFS). The results showed that on Aug. 8, 2017 in Hohhot there would appear scattering convective clouds, with cold-warm mixed vertical structure and strong updrafts. Horizontal scale of single convective cloud was about tens of kilometers, lifetime was about 1.5-3 hours. Cloud top (bottom) height of 10 (3) km, 0℃ height of 4.3 km. Cloud microphysics aspects were with high content of snow and graupel, low cloud water content in warm regions, maximum content of supercooled water of 0.7 g·kg-1, less ice crystals in areas with rich supercooled water, mainly with cold precipitation mechanism. Convective clouds were first appeared in the northwest direction of the core zone in Hohhot, rapidly developed and moved eastward and southward gradually to the core zone with speed about 30-40 km·h-1. Satellite and radar observation also showed there were convective clouds. The generation time of convective clouds of forecast was 1-2 hours later than the observation, and moving direction was consistent with observation. Moving speed was 10-20 km·h-1 slower. The maximum liquid water content was 0.6 g·m– 3 at 5400 m height (-8℃) by airborne cloud physical detection. Cloud water content of forecast was consistent with detection. The reserve seeding plan was made based on cloud condition forecast. 50-30 km northwest of the core zone was chosen as key defense zone. AgI over-seeding would suitable to be implemented during 5.1-7.0 km height. In the morning of Aug. 8, the aircraft would carry out detection in weak echo areas of the first defense line. Ground operations would focus on the implementation of over-seeding in the initial stage of convective clouds in the third defense line to achieve the goal of rainfall mitigation. Based on the reserve plan, additional five sets of ground mobile seeding equipment had been added to reinforce the capability of rainfall mitigation ahead of 24 hours of target time. Rainfall mitigation was carried out with the 5 sets equipment. In summary, cloud seeding condition forecast was proper, reserve seeding plan services was reasonable, which provided strong support for field rainfall mitigation action.
In order to do well artificial rainfall mitigation on specific target period and area, cloud seeding condition such as cloud properties and structure, moving speed and direction, cloud evolution, precipitation mechanism and so on was forecast by using Cloud Precipitation Explicit Forecast System (CPEFS). The results showed that on Aug. 8, 2017 in Hohhot there would appear scattering convective clouds, with cold-warm mixed vertical structure and strong updrafts. Horizontal scale of single convective cloud was about tens of kilometers, lifetime was about 1.5-3 hours. Cloud top (bottom) height of 10 (3) km, 0℃ height of 4.3 km. Cloud microphysics aspects were with high content of snow and graupel, low cloud water content in warm regions, maximum content of supercooled water of 0.7 g·kg-1, less ice crystals in areas with rich supercooled water, mainly with cold precipitation mechanism. Convective clouds were first appeared in the northwest direction of the core zone in Hohhot, rapidly developed and moved eastward and southward gradually to the core zone with speed about 30-40 km·h-1. Satellite and radar observation also showed there were convective clouds. The generation time of convective clouds of forecast was 1-2 hours later than the observation, and moving direction was consistent with observation. Moving speed was 10-20 km·h-1 slower. The maximum liquid water content was 0.6 g·m– 3 at 5400 m height (-8℃) by airborne cloud physical detection. Cloud water content of forecast was consistent with detection. The reserve seeding plan was made based on cloud condition forecast. 50-30 km northwest of the core zone was chosen as key defense zone. AgI over-seeding would suitable to be implemented during 5.1-7.0 km height. In the morning of Aug. 8, the aircraft would carry out detection in weak echo areas of the first defense line. Ground operations would focus on the implementation of over-seeding in the initial stage of convective clouds in the third defense line to achieve the goal of rainfall mitigation. Based on the reserve plan, additional five sets of ground mobile seeding equipment had been added to reinforce the capability of rainfall mitigation ahead of 24 hours of target time. Rainfall mitigation was carried out with the 5 sets equipment. In summary, cloud seeding condition forecast was proper, reserve seeding plan services was reasonable, which provided strong support for field rainfall mitigation action.
Abstract:
Using the observation data obtained by the 90 m height wind tower in Xilian Town, Xuwen County, Guangdong Province during landfall of super strong typhoon Rammasun, the characteristics of strong wind in surface layer of typhoon Rammasun are analyzed. The results show that: (1) The wind speed at different heights presents clear “M” pattern. The wind direction counterclockwise deflects about 170° before and after the typhoon center passed through the wind tower. (2) The wind speed increases with the increase of height, and the wind speed profile fits well with the laws of logarithm and power index. Wind shear index and roughness length decrease first from front outer-vortex to front eye-wall and then gradually increase in the wind eye, back eye-wall and back outer-vortex. (3) In the strong wind process of typhoon, the turbulence intensity and gust factor are larger in front or back outer-vortex, and smaller in the front or back eye-wall. The turbulence intensity and gust factor decrease with the increase of height, which basically accords with the power law with negative exponent. (4) The variation of the 10min wind direction is more stable compared with that in wind eye which is rather intense. The wind speed is lowest in wind eye while the variations of the 10min wind direction reach the maximum value.
Using the observation data obtained by the 90 m height wind tower in Xilian Town, Xuwen County, Guangdong Province during landfall of super strong typhoon Rammasun, the characteristics of strong wind in surface layer of typhoon Rammasun are analyzed. The results show that: (1) The wind speed at different heights presents clear “M” pattern. The wind direction counterclockwise deflects about 170° before and after the typhoon center passed through the wind tower. (2) The wind speed increases with the increase of height, and the wind speed profile fits well with the laws of logarithm and power index. Wind shear index and roughness length decrease first from front outer-vortex to front eye-wall and then gradually increase in the wind eye, back eye-wall and back outer-vortex. (3) In the strong wind process of typhoon, the turbulence intensity and gust factor are larger in front or back outer-vortex, and smaller in the front or back eye-wall. The turbulence intensity and gust factor decrease with the increase of height, which basically accords with the power law with negative exponent. (4) The variation of the 10min wind direction is more stable compared with that in wind eye which is rather intense. The wind speed is lowest in wind eye while the variations of the 10min wind direction reach the maximum value.
Abstract:
A fire inventory, surface monitoring data and numerical models were used to analyze the biomass burning aerosol (BBA) emissions in Indochina peninsula and their effects on haze in Southwest China and pre-monsoon precipitation in South China. The BBA emissions in Indochina peninsula mainly occurred in March and April each year, and the peak emissions were in late March to early April. Eastern Myanmar and Northern Laos dominated the BBA emissions. The BBA in Indochina Peninsula mainly affected the haze in the southern cities of Yunnan, China at the surface. The emissions from Myanmar were the most significant contributor to the pollution in these cities. The BBA in Indochina Peninsula could be transported over most parts of Southern China by the low-level southwest rapids at the height from 800 hPa to 600 hPa. The transported BBA over Southern China could alter the spatial fraction of the pre-monsoon precipitation process by suppressing the convective precipitation and enhancing the non-convective precipitation, and then precipitation was more concentrated near the shear line.
A fire inventory, surface monitoring data and numerical models were used to analyze the biomass burning aerosol (BBA) emissions in Indochina peninsula and their effects on haze in Southwest China and pre-monsoon precipitation in South China. The BBA emissions in Indochina peninsula mainly occurred in March and April each year, and the peak emissions were in late March to early April. Eastern Myanmar and Northern Laos dominated the BBA emissions. The BBA in Indochina Peninsula mainly affected the haze in the southern cities of Yunnan, China at the surface. The emissions from Myanmar were the most significant contributor to the pollution in these cities. The BBA in Indochina Peninsula could be transported over most parts of Southern China by the low-level southwest rapids at the height from 800 hPa to 600 hPa. The transported BBA over Southern China could alter the spatial fraction of the pre-monsoon precipitation process by suppressing the convective precipitation and enhancing the non-convective precipitation, and then precipitation was more concentrated near the shear line.
Abstract:
An extreme gale event, hereinafter referred to as“3.21 Lingui gale event”, occurred in Lingui, Guangxi on 21 March 2019, Maximum gust of 60.3 m?s-1 (level 17) was recorded at the Lingui Observatory at 21:13. Based on the results of the wind damage survey with video and meteorological data, this paper presents that the high wind damage was caused by a strong microburst. Using data from conventional meteorological observations, intensive automatic weather station, radiosonde, Doppler weather radar, we have analyzed the environmental conditions and influencing systems of the“3.21 Lingui gale event”, with special emphasis on analyzing its cause based radar data and observational data. Results are as follows.(1) The “3.21 Lingui gale event” occurred under some favorable conditions such as Low-level warm and humid air flow is active, Mid-level significant dry layer and strong low-level vertical wind shear, and it is triggered by the development of convergence line at ground level and cold front.(2) “3.21 Lingui gale event” is caused by 2 in 1 supercell, Before the downburst occurs, the supercell develops to the most powerful stage, the maximum reflectivity core height (HGT) is more than 6 km, there is a medium intensity of the mesocyclone accompanied by the MARC value of 36 m?s-1. When the downbursts occurs ,reflectivity factor begins to weaken, the storm top drops high, HGT drops. when HGT drops sharply, a body sweep interval drops by 3.5 km, 17 thumps occur, and the low level 0.5 degrees elevation is observed in the high-altitude region of the cyclone, with a high radial dispersion value of 27 m?s-1, Mesocyclone has the strongest shear strengthening, the bottom high height rapidly dropped to less than 1km and other characteristics. (3) The occurrence of downburst is closely related to the dragging effect of extreme heavy precipitation and hail, When 1min rain strength of 3 mm, wind speed of more than 12 levels, 1min rain strong 6 mm, 17 degrees of extreme wind speed.
An extreme gale event, hereinafter referred to as“3.21 Lingui gale event”, occurred in Lingui, Guangxi on 21 March 2019, Maximum gust of 60.3 m?s-1 (level 17) was recorded at the Lingui Observatory at 21:13. Based on the results of the wind damage survey with video and meteorological data, this paper presents that the high wind damage was caused by a strong microburst. Using data from conventional meteorological observations, intensive automatic weather station, radiosonde, Doppler weather radar, we have analyzed the environmental conditions and influencing systems of the“3.21 Lingui gale event”, with special emphasis on analyzing its cause based radar data and observational data. Results are as follows.(1) The “3.21 Lingui gale event” occurred under some favorable conditions such as Low-level warm and humid air flow is active, Mid-level significant dry layer and strong low-level vertical wind shear, and it is triggered by the development of convergence line at ground level and cold front.(2) “3.21 Lingui gale event” is caused by 2 in 1 supercell, Before the downburst occurs, the supercell develops to the most powerful stage, the maximum reflectivity core height (HGT) is more than 6 km, there is a medium intensity of the mesocyclone accompanied by the MARC value of 36 m?s-1. When the downbursts occurs ,reflectivity factor begins to weaken, the storm top drops high, HGT drops. when HGT drops sharply, a body sweep interval drops by 3.5 km, 17 thumps occur, and the low level 0.5 degrees elevation is observed in the high-altitude region of the cyclone, with a high radial dispersion value of 27 m?s-1, Mesocyclone has the strongest shear strengthening, the bottom high height rapidly dropped to less than 1km and other characteristics. (3) The occurrence of downburst is closely related to the dragging effect of extreme heavy precipitation and hail, When 1min rain strength of 3 mm, wind speed of more than 12 levels, 1min rain strong 6 mm, 17 degrees of extreme wind speed.
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The characteristics of precipitation fog process causing low visibility weather are analyzed by using millimeter wave radar detection. Analysis of horizontal distribution characteristics of the process shows that the spatial scale is about 15 km, and the radar wave intensity ranges from -20 dBz to 25 dBz. The vertical structure of the process is analyzed and displayed that the process has experienced a series of transition processes from precipitation to fog as it passes through. The analysis of radar radial velocity shows that the main structure of the system is stable, and the edge area is compensated for the main area, so that the system can maintain and develop. The visibility of the ground visibility station begins to decline as the process approaches and minimizes when the process is about to leave. And visibility is restored after the system has been away for a period of time. No effective precipitation was observed in the scanning area of millimeter wave radar as the system passed. According to the empirical formula, the relationship between radar reflectivity intensity of low altitude and visibility of stations is simulated, and the specific formula is .
The characteristics of precipitation fog process causing low visibility weather are analyzed by using millimeter wave radar detection. Analysis of horizontal distribution characteristics of the process shows that the spatial scale is about 15 km, and the radar wave intensity ranges from -20 dBz to 25 dBz. The vertical structure of the process is analyzed and displayed that the process has experienced a series of transition processes from precipitation to fog as it passes through. The analysis of radar radial velocity shows that the main structure of the system is stable, and the edge area is compensated for the main area, so that the system can maintain and develop. The visibility of the ground visibility station begins to decline as the process approaches and minimizes when the process is about to leave. And visibility is restored after the system has been away for a period of time. No effective precipitation was observed in the scanning area of millimeter wave radar as the system passed. According to the empirical formula, the relationship between radar reflectivity intensity of low altitude and visibility of stations is simulated, and the specific formula is .
Abstract:
This paper try to apply deep learning method on establishing a model to discriminate the precipitation type. Hundreds of thousands of precipitation samples obtained from sounding and observation data of China from 1996 to 2015 was treated to be rain and snow. Data from 2016 to 2017 were tested, and a case test was conducted for a rain and snow weather process over China in late January 2018. Furthermore, the application of deep learning method to discrimination and forecasting of precipitation type are discussed. The main conclusions are as follows. Discrimination accuracy of the model is 98.2%, which is significantly improved the traditional index threshold method. Moreover, TS scores of rain and snow are 97.4% and 94.4%, false discriminate rates are 1.7% and 2.0%, omission rates are 1.0% and 3.7%, respectively. The model discrimination results based on the real data are basically consistent with the real data, analyzed by the rain and snow weather process over China in late January 2018. The results also have a good forecast performance of precipitation type over China, which based on ECMWF precipitation type products and the model results based on the forecast data in next 24 hours. Compared with ECMWF, the forecast of the model to rain and snow separating line are more consistent with observations generally. The test results show that the discrimination model established in this paper can extract the key features of precipitation type of rain and snow. The application of deep learning method to discrimination and forecasting of precipitation type is feasible and advantageous. This method can provide important technical support for the objective identification and prediction of precipitation type.
This paper try to apply deep learning method on establishing a model to discriminate the precipitation type. Hundreds of thousands of precipitation samples obtained from sounding and observation data of China from 1996 to 2015 was treated to be rain and snow. Data from 2016 to 2017 were tested, and a case test was conducted for a rain and snow weather process over China in late January 2018. Furthermore, the application of deep learning method to discrimination and forecasting of precipitation type are discussed. The main conclusions are as follows. Discrimination accuracy of the model is 98.2%, which is significantly improved the traditional index threshold method. Moreover, TS scores of rain and snow are 97.4% and 94.4%, false discriminate rates are 1.7% and 2.0%, omission rates are 1.0% and 3.7%, respectively. The model discrimination results based on the real data are basically consistent with the real data, analyzed by the rain and snow weather process over China in late January 2018. The results also have a good forecast performance of precipitation type over China, which based on ECMWF precipitation type products and the model results based on the forecast data in next 24 hours. Compared with ECMWF, the forecast of the model to rain and snow separating line are more consistent with observations generally. The test results show that the discrimination model established in this paper can extract the key features of precipitation type of rain and snow. The application of deep learning method to discrimination and forecasting of precipitation type is feasible and advantageous. This method can provide important technical support for the objective identification and prediction of precipitation type.
Abstract:
Previous literatures suggest that El Nin ?o is a dominant factor causing spring drought in Yunnan province. Under the background of super-strong El Ni?o event during 2015, the spring (March-May) precipitation in most parts of western Yunnan province is below normal, and the rainy season starts late to very late. However, the precipitation in eastern part is generally abundant, and the rainy seasons in some regions start early to very early, presenting a sharp contrast between the east and west. By using daily rain gauge precipitation of Yunnan province, the CPC (Climate Prediction Center, USA) Global Unified Gauge-Based Analysis of Daily Precipitation and NCEP/NCAR (National Centers for Environmental Prediction/ National Center for Atmospheric Research) reanalysis data, the influence of 10-30-day atmospheric oscillation on the spring abnormal precipitation over eastern Yunnan was studied through statistical and dynamical diagnosis methods. The analysis showed that the 10-30-day oscillation was active to the east of 100°E, from mid-March to late-April, which is a major reason for the abnormal abundant precipitation over eastern Yunnan. Three distinct precipitation processes in eastern Yunnan happened associated with the southward approaching of the low-frequency cold cell that embedded in the Eurasian pattern (EU) wave train from the mid- and high- latitudes of East Asia. Namely, when the upward branch of the secondary circulation around the subtropical westerly jet entrance interacted with the reflux vapor on the southwestern fringe of the cold high, the rainfall process was formed.
Previous literatures suggest that El Nin ?o is a dominant factor causing spring drought in Yunnan province. Under the background of super-strong El Ni?o event during 2015, the spring (March-May) precipitation in most parts of western Yunnan province is below normal, and the rainy season starts late to very late. However, the precipitation in eastern part is generally abundant, and the rainy seasons in some regions start early to very early, presenting a sharp contrast between the east and west. By using daily rain gauge precipitation of Yunnan province, the CPC (Climate Prediction Center, USA) Global Unified Gauge-Based Analysis of Daily Precipitation and NCEP/NCAR (National Centers for Environmental Prediction/ National Center for Atmospheric Research) reanalysis data, the influence of 10-30-day atmospheric oscillation on the spring abnormal precipitation over eastern Yunnan was studied through statistical and dynamical diagnosis methods. The analysis showed that the 10-30-day oscillation was active to the east of 100°E, from mid-March to late-April, which is a major reason for the abnormal abundant precipitation over eastern Yunnan. Three distinct precipitation processes in eastern Yunnan happened associated with the southward approaching of the low-frequency cold cell that embedded in the Eurasian pattern (EU) wave train from the mid- and high- latitudes of East Asia. Namely, when the upward branch of the secondary circulation around the subtropical westerly jet entrance interacted with the reflux vapor on the southwestern fringe of the cold high, the rainfall process was formed.
Abstract:
Based on the data of automatic weather station, wind-profiling radar, ERA5 reanalysis, himawari 8 high resolution satellite and FM-120 fog droplet spectrometer, we discussed the circulation pattern and microphysical processes of an seafog event in southern coastal area of Fujian in April 7th 2019. Circulation analysis showed that this sea fog event occurs under the control of west to northwest flow of 500 hPa trough bottom, while 700 hPa to surface was uniform southerly flow. The sounding situation is stable. Before sea fog event, low level wind speed decreased significantly, increasing the thickness of low wind speed, which provided stable circulation for sea fog. Himawari 8 satellite images showed that the sea fog rapidly formed on straits first and then advected to coastal area by low level southerly airflow. Hydrological analysis indicated that there existed a cold water band and large temperature gradient near shore. Sea surface temperature(SST) varied between 18 to 24 ℃. Air sea temperature difference varied between 0 to 2 ℃ with sea surface colder than the air above, which contributed to advection sea fog forming. Fog droplet spectrum analysis showed that visibility decreased dramatically while Particle number concentration (PNC), liquid water content (LWC) and droplet spectrum increased significantly at the same time. During the sea fog process, five-minute average PNC exceeded 200 #?cm-3 and instantaneously reached 468 #?cm-3 maximum, Process average PNC reached 100 #?cm-3. Five-minute averaged LWC reached 0.41 g?m-3 and 1.35 g?m-3 instantaneously. Process average LWC reached 0.17 g?m-3. Fog droplet size exhibited double peak characteristic during the fog process with 4～6 μm and 22～26 μm interval. This proved that small and big particles both contributed to the formation of sea fog.
Based on the data of automatic weather station, wind-profiling radar, ERA5 reanalysis, himawari 8 high resolution satellite and FM-120 fog droplet spectrometer, we discussed the circulation pattern and microphysical processes of an seafog event in southern coastal area of Fujian in April 7th 2019. Circulation analysis showed that this sea fog event occurs under the control of west to northwest flow of 500 hPa trough bottom, while 700 hPa to surface was uniform southerly flow. The sounding situation is stable. Before sea fog event, low level wind speed decreased significantly, increasing the thickness of low wind speed, which provided stable circulation for sea fog. Himawari 8 satellite images showed that the sea fog rapidly formed on straits first and then advected to coastal area by low level southerly airflow. Hydrological analysis indicated that there existed a cold water band and large temperature gradient near shore. Sea surface temperature(SST) varied between 18 to 24 ℃. Air sea temperature difference varied between 0 to 2 ℃ with sea surface colder than the air above, which contributed to advection sea fog forming. Fog droplet spectrum analysis showed that visibility decreased dramatically while Particle number concentration (PNC), liquid water content (LWC) and droplet spectrum increased significantly at the same time. During the sea fog process, five-minute average PNC exceeded 200 #?cm-3 and instantaneously reached 468 #?cm-3 maximum, Process average PNC reached 100 #?cm-3. Five-minute averaged LWC reached 0.41 g?m-3 and 1.35 g?m-3 instantaneously. Process average LWC reached 0.17 g?m-3. Fog droplet size exhibited double peak characteristic during the fog process with 4～6 μm and 22～26 μm interval. This proved that small and big particles both contributed to the formation of sea fog.
Abstract:
Using 219 effective short time strong rainfall at national station and 7 Doppler weather radar data in Yunnan province from May to October in 2014 to 2016. The short time strong rainfall in the periphery of the subtropical high in Yunnan province is further subdivided into two high convergence category, simple periphery of the subtropical high category and the west side of subtropical high with westerly trough category. Preliminary conclusions are as follows: August is the high incidence period of short-time strong rainfall in the periphery of the subtropical high in Yunnan province, and the precipitation period is concentrated in the afternoon and the first half of the night. The two high convergence precipitation distributes along the convergence area, with strong precipitation and relatively concentrated falling area. The simple periphery of the subtropical high precipitation mainly located in southern Yunnan, manifested as three large value regions. The west side of subtropical high with westerly trough precipitation is mainly located at the edge of Yunnan province, while the area is scattered. The average intensity of the three types of precipitation echoes is between 35 and 45 dBz, average duration of 9 volume scan. Nearly a quarter of the echoes appears inclination and strong echo gradient, and the precipitation is obviously stronger than the echo which does not appear. In a way that can be uesd as a basis for judging the intensity of precipitation. The occurrence time of the strongest ET and VIL of the three types of precipitation is basically the same time as that of the strongest echo, or slightly lagged behind. Nearly half of the two high convergence VWPs have southwesterly or westerly airflow in the lower layer, which corresponds to the obvious characteristics of warm advection. With the development of precipitation, The disappearance of no-data area corresponding to the clear sky area around the subtropical high is the most obvious feature of VWP of precipitation in the simple periphery of the subtropical high.. For the west side of subtropical high with westerly trough category, whether precipitation begins or not, invasion of upper northwest airflow and middle-level wind shear are both exist. Corresponds to the cold advection brought by the rear of the low trough and the intersection of warm and cold air currents.
Using 219 effective short time strong rainfall at national station and 7 Doppler weather radar data in Yunnan province from May to October in 2014 to 2016. The short time strong rainfall in the periphery of the subtropical high in Yunnan province is further subdivided into two high convergence category, simple periphery of the subtropical high category and the west side of subtropical high with westerly trough category. Preliminary conclusions are as follows: August is the high incidence period of short-time strong rainfall in the periphery of the subtropical high in Yunnan province, and the precipitation period is concentrated in the afternoon and the first half of the night. The two high convergence precipitation distributes along the convergence area, with strong precipitation and relatively concentrated falling area. The simple periphery of the subtropical high precipitation mainly located in southern Yunnan, manifested as three large value regions. The west side of subtropical high with westerly trough precipitation is mainly located at the edge of Yunnan province, while the area is scattered. The average intensity of the three types of precipitation echoes is between 35 and 45 dBz, average duration of 9 volume scan. Nearly a quarter of the echoes appears inclination and strong echo gradient, and the precipitation is obviously stronger than the echo which does not appear. In a way that can be uesd as a basis for judging the intensity of precipitation. The occurrence time of the strongest ET and VIL of the three types of precipitation is basically the same time as that of the strongest echo, or slightly lagged behind. Nearly half of the two high convergence VWPs have southwesterly or westerly airflow in the lower layer, which corresponds to the obvious characteristics of warm advection. With the development of precipitation, The disappearance of no-data area corresponding to the clear sky area around the subtropical high is the most obvious feature of VWP of precipitation in the simple periphery of the subtropical high.. For the west side of subtropical high with westerly trough category, whether precipitation begins or not, invasion of upper northwest airflow and middle-level wind shear are both exist. Corresponds to the cold advection brought by the rear of the low trough and the intersection of warm and cold air currents.
Abstract:
Based on the observation data from agro-meteorological stations from 1981 to 2016 in Heilongjiang province,By using the indicators of water deficiency index(KCWDI) and accumulated temperature anomaly ≥10℃ from the People"s Republic of China meteorological industry standards for assessment of drought and cold damage to maize during seedling-milk ripening stage separately, this paper stipulated that drought and cold damage cross-stress occurred in the same year in the same station, and the temporal and spatial distribution of it were analyzed. The relational model between KCWDI, accumulated temperature anomaly ≥10℃ and maize yield was constructed by mathematical statistical method, and the effects of two kinds of disasters on maize yield were investigated by comparative method. The results showed that KCWDI fluctuated and declined(P＞0.05), and its longitude change was that KCWDI was high in the west and it was low in the East during maize seedling-seventh leaf period in the study area, and accumulated temperature anomaly ≥10℃ increased(P＜0.01)from 1981 to 2016, and the latitudeSchange was that accumulated temperature anomaly ≥10℃ was low in the north and it was high in the south. The Change of this two kind of disaster indicators was consistent with spatial distribution of water resources and climate warming trend in the research area; During the analysis period, the sum of years of drought and cold damage
Based on the observation data from agro-meteorological stations from 1981 to 2016 in Heilongjiang province,By using the indicators of water deficiency index(KCWDI) and accumulated temperature anomaly ≥10℃ from the People"s Republic of China meteorological industry standards for assessment of drought and cold damage to maize during seedling-milk ripening stage separately, this paper stipulated that drought and cold damage cross-stress occurred in the same year in the same station, and the temporal and spatial distribution of it were analyzed. The relational model between KCWDI, accumulated temperature anomaly ≥10℃ and maize yield was constructed by mathematical statistical method, and the effects of two kinds of disasters on maize yield were investigated by comparative method. The results showed that KCWDI fluctuated and declined(P＞0.05), and its longitude change was that KCWDI was high in the west and it was low in the East during maize seedling-seventh leaf period in the study area, and accumulated temperature anomaly ≥10℃ increased(P＜0.01)from 1981 to 2016, and the latitudeSchange was that accumulated temperature anomaly ≥10℃ was low in the north and it was high in the south. The Change of this two kind of disaster indicators was consistent with spatial distribution of water resources and climate warming trend in the research area; During the analysis period, the sum of years of drought and cold damage
Abstract:
In 21 March 2019, an instantaneous wind speed of 60.3 ms-1 was recorded at 2113 LST by national observation station in Lingui District, Guangxi Province. In 13 April 2019, an instantaneous wind speed of 50.7 ms-1 was recorded at 1411 LST by observation station in Hean Town, Guangdong Province. Significant wind damage was observed at two places. Based on surveillance video record, UAV aerial image and on-site investigation, it can be concluded as follow:(1) The wind damage occurred at Lingui national meteorological observation station and its surrounding area at 2108-2114 LST 23 March is due to a microburst at EF2 scale in time scale of 7 minutes and spatial scale of 1.6 km×2.0 km. It belongs to micro-α scale and contained seven micro-β scale swans. The damage area is featured with small aspect ratio, discontinuous spatial distribution and divergent wind pattern. (2) The wind damage occurred at 1408-1415 LST, 13 April in Xuwen, Guangdong Province was a tornado at EF3 scale in time scale of 8 minutes. The damage swath was ~3.2km long and 30-280m wide. The surveillance video showed that there was a rotational wind tunnel existed shortly near the damage site. The damage area has larger aspect ratio, continuous spatial distribution and convergent wind pattern.
In 21 March 2019, an instantaneous wind speed of 60.3 ms-1 was recorded at 2113 LST by national observation station in Lingui District, Guangxi Province. In 13 April 2019, an instantaneous wind speed of 50.7 ms-1 was recorded at 1411 LST by observation station in Hean Town, Guangdong Province. Significant wind damage was observed at two places. Based on surveillance video record, UAV aerial image and on-site investigation, it can be concluded as follow:(1) The wind damage occurred at Lingui national meteorological observation station and its surrounding area at 2108-2114 LST 23 March is due to a microburst at EF2 scale in time scale of 7 minutes and spatial scale of 1.6 km×2.0 km. It belongs to micro-α scale and contained seven micro-β scale swans. The damage area is featured with small aspect ratio, discontinuous spatial distribution and divergent wind pattern. (2) The wind damage occurred at 1408-1415 LST, 13 April in Xuwen, Guangdong Province was a tornado at EF3 scale in time scale of 8 minutes. The damage swath was ~3.2km long and 30-280m wide. The surveillance video showed that there was a rotational wind tunnel existed shortly near the damage site. The damage area has larger aspect ratio, continuous spatial distribution and convergent wind pattern.
Abstract:
Based on Prata parameterization of clear sky downward longwave radiation and in view of its poor theoretical accuracy in plateau areas and areas with small precipitable water vapor, three new parameterizations of clear sky downward longwave radiation are proposed in this paper, in which air pressure is considered because longwave radiation from different length of atmosphere column is different. Empirical constants are obtained by least square fitting of global ERA-5 reanalysis data and their applicability is analyzed in different regions of the world. The simulation results show that parameterizations with consideration of air pressure can effectively improve the convergence of atmospheric emissivity of prata scheme when the precipitable water vapor can be reduced. The mean bias errors and the root mean square errors of the simulation values of the downward longwave radiation of the new schemes in Amdo area and San Luis from the observation value areobviously smaller than that of Prata’s parameterization scheme. Compared with Prata scheme, the simulation accuracy of the new schemes are improved and the applicability is better.
Based on Prata parameterization of clear sky downward longwave radiation and in view of its poor theoretical accuracy in plateau areas and areas with small precipitable water vapor, three new parameterizations of clear sky downward longwave radiation are proposed in this paper, in which air pressure is considered because longwave radiation from different length of atmosphere column is different. Empirical constants are obtained by least square fitting of global ERA-5 reanalysis data and their applicability is analyzed in different regions of the world. The simulation results show that parameterizations with consideration of air pressure can effectively improve the convergence of atmospheric emissivity of prata scheme when the precipitable water vapor can be reduced. The mean bias errors and the root mean square errors of the simulation values of the downward longwave radiation of the new schemes in Amdo area and San Luis from the observation value areobviously smaller than that of Prata’s parameterization scheme. Compared with Prata scheme, the simulation accuracy of the new schemes are improved and the applicability is better.
Abstract:
Extremely severe precipitation would cause disaster easily.The occurrence of extremely severe precipitation in the south China coast is closely related to the boundary layer jet stream.At present, the forecast of extremely heavy precipitation is still the emphasis and difficulty in service.This study is based on meteorological monitoring stations in Guangdong Province and global reanalysis data CFSR,and the process of two record-breaking extremely severe precipitation events of August 2013 and August 2018 in eastern region of Guangdong is analyzed, to expound the effect of boundary layer jet.The result is shown as follows.(1)The main influence systems of the two processes respectively were the long slowly moving residual circulation of typhoon Utor and outer circulation of monsoon depression.When the eastern region of Guangdong was located on the southeast side of typhoon circulation or the east side of monsoon depression,the convergence and uplift of boundary layer jet formed a clear mesoscale energy front,and the atmospheric baroclinicity of that region was enhanced,the severe rainfall was under favorable conditions to trigger and maintain.(2)Boundary layer jet provides abundant and continuous water vapor conditions for heavy rainfall,cooperated with the effect of special topographic friction and countercheck,remarkable convergence of water vapor flux was formed in the in eastern region of Guangdong.(3)Weak boundary layer wind vertical shear and the significant temperature front made atmosphere in eastern region of Guangdong to keep an unstable state.Long time instability of the stratified atmosphere was conducive to the maintenance of severe rainfall.(4) The maintenance or northward moving of surface mesoscale convergence lines made the echoes of heavy rainfall constantly trigger and maintain.The difference between the two processes mainly showed as difference of the boundary layer jet intensity and the wind direction,thus the way of airflow convergence and scope of severe rainfall were significantly different.The role of boundary layer jet performed more significantly during the influence process of monsoon depression.The study results are helpful to understand the formation mechanism of extremely heavy precipitation in the rainstorm center in eastern region of Guangdong,and to provide strong meteorological safeguard and service in future.
Extremely severe precipitation would cause disaster easily.The occurrence of extremely severe precipitation in the south China coast is closely related to the boundary layer jet stream.At present, the forecast of extremely heavy precipitation is still the emphasis and difficulty in service.This study is based on meteorological monitoring stations in Guangdong Province and global reanalysis data CFSR,and the process of two record-breaking extremely severe precipitation events of August 2013 and August 2018 in eastern region of Guangdong is analyzed, to expound the effect of boundary layer jet.The result is shown as follows.(1)The main influence systems of the two processes respectively were the long slowly moving residual circulation of typhoon Utor and outer circulation of monsoon depression.When the eastern region of Guangdong was located on the southeast side of typhoon circulation or the east side of monsoon depression,the convergence and uplift of boundary layer jet formed a clear mesoscale energy front,and the atmospheric baroclinicity of that region was enhanced,the severe rainfall was under favorable conditions to trigger and maintain.(2)Boundary layer jet provides abundant and continuous water vapor conditions for heavy rainfall,cooperated with the effect of special topographic friction and countercheck,remarkable convergence of water vapor flux was formed in the in eastern region of Guangdong.(3)Weak boundary layer wind vertical shear and the significant temperature front made atmosphere in eastern region of Guangdong to keep an unstable state.Long time instability of the stratified atmosphere was conducive to the maintenance of severe rainfall.(4) The maintenance or northward moving of surface mesoscale convergence lines made the echoes of heavy rainfall constantly trigger and maintain.The difference between the two processes mainly showed as difference of the boundary layer jet intensity and the wind direction,thus the way of airflow convergence and scope of severe rainfall were significantly different.The role of boundary layer jet performed more significantly during the influence process of monsoon depression.The study results are helpful to understand the formation mechanism of extremely heavy precipitation in the rainstorm center in eastern region of Guangdong,and to provide strong meteorological safeguard and service in future.
Abstract:
An EF3 tornado struck Xuwen County of Zhanzhang city, Guangdong Province on 13 April 2019. The tornado path was about 16 km long and lasted about 36 minutes, resulting in one fatality and five injuries. In this paper, the Characteristics of the environmental field and radar echo of the strong tornado are analyzed by using a variety of observational data such as high density regional automatic weather stations and doppler radar observations. The results show that the mesoscale convective system producing tornado supercell occurs in front of the surface warm and low pressure trough, and there is a significant convergence of southwest airflow and southerly jet in the middle and lower layers. It has typical strong convective circulation situations such as low-level convergence, high-level divergence and high temperature and humidity. The environmental conditions are characterized by strong vertical wind shear, low lifting condensation level, large storm relative helicity and large energy helicity. When the tornado affects, the meteorological elements of the automatic weather station show obvious signals, such as steep drop and steep rise of air pressure, cyclonic rotation of wind direction, sudden increase of wind speed, obvious drop of temperature, etc. Tornado occurs in a supercell storm with positive Cloud-to-Ground lightning and high cell centroid. There are low-level strong mesocyclone and TVS, as well as hook echo and echo pendency. Tornado occurs near the top of the hook echo. High resolution satellite infrared images show that tornado occurs at the maximum blackbody temperature gradient of meso-β scale convective system edge.
An EF3 tornado struck Xuwen County of Zhanzhang city, Guangdong Province on 13 April 2019. The tornado path was about 16 km long and lasted about 36 minutes, resulting in one fatality and five injuries. In this paper, the Characteristics of the environmental field and radar echo of the strong tornado are analyzed by using a variety of observational data such as high density regional automatic weather stations and doppler radar observations. The results show that the mesoscale convective system producing tornado supercell occurs in front of the surface warm and low pressure trough, and there is a significant convergence of southwest airflow and southerly jet in the middle and lower layers. It has typical strong convective circulation situations such as low-level convergence, high-level divergence and high temperature and humidity. The environmental conditions are characterized by strong vertical wind shear, low lifting condensation level, large storm relative helicity and large energy helicity. When the tornado affects, the meteorological elements of the automatic weather station show obvious signals, such as steep drop and steep rise of air pressure, cyclonic rotation of wind direction, sudden increase of wind speed, obvious drop of temperature, etc. Tornado occurs in a supercell storm with positive Cloud-to-Ground lightning and high cell centroid. There are low-level strong mesocyclone and TVS, as well as hook echo and echo pendency. Tornado occurs near the top of the hook echo. High resolution satellite infrared images show that tornado occurs at the maximum blackbody temperature gradient of meso-β scale convective system edge.
Abstract:
Due to the influence of underlying surface and other factors, the raindrop size distribution characteristics of rainfall in mountainous and plain areas sometimes have great differences. The analysis of the differences between them is helpful to understand the characteristics of rainfall in depth. Based on the raindrop spectrum data from laser optical disdrometer and rainfall data from automatic station over Beijing in the summer of 2017 and 2018, the representative mountain area Yanqing station and plain area Daxing station were selected. The raindrop size distribution characteristics of convective and stratiform rain types at two stations were studied by rain type classification method. The results show that the summer rainfall in Beijing area is mainly weak rainfall, but convective rain contributed to the main rainfall. The composite spectra of two stations are both single peak structure, and Gamma distribution fit the composite spectra well. Compared with different rain types, convective rain spectra has larger Dm, LgNw and distribution spectrum width (SD) than stratiform rain spectra. Compared with the two stations, the Dm (LgNw) of different rain types at Yanqing Station is larger than (less than) that of Daxing Station, indicating that the mountain area raindrop size is larger while number concentration is lower; the convective rain spectrum at mountain (plain) area is more inclined to the continental (maritime) convective. The relationship between Dm-R, LgNw-R, μ(shape)-Λ (slope)and Z-R were also analyzed . The standard Z-R relation Z=300R1.4has good fitting effect for both stations, which indicates that this relation is suitable for Beijing area.
Due to the influence of underlying surface and other factors, the raindrop size distribution characteristics of rainfall in mountainous and plain areas sometimes have great differences. The analysis of the differences between them is helpful to understand the characteristics of rainfall in depth. Based on the raindrop spectrum data from laser optical disdrometer and rainfall data from automatic station over Beijing in the summer of 2017 and 2018, the representative mountain area Yanqing station and plain area Daxing station were selected. The raindrop size distribution characteristics of convective and stratiform rain types at two stations were studied by rain type classification method. The results show that the summer rainfall in Beijing area is mainly weak rainfall, but convective rain contributed to the main rainfall. The composite spectra of two stations are both single peak structure, and Gamma distribution fit the composite spectra well. Compared with different rain types, convective rain spectra has larger Dm, LgNw and distribution spectrum width (SD) than stratiform rain spectra. Compared with the two stations, the Dm (LgNw) of different rain types at Yanqing Station is larger than (less than) that of Daxing Station, indicating that the mountain area raindrop size is larger while number concentration is lower; the convective rain spectrum at mountain (plain) area is more inclined to the continental (maritime) convective. The relationship between Dm-R, LgNw-R, μ(shape)-Λ (slope)and Z-R were also analyzed . The standard Z-R relation Z=300R1.4has good fitting effect for both stations, which indicates that this relation is suitable for Beijing area.
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2012,38(12):1482-1491, DOI: 10.7519/j.issn.1000-0526.2012.12.005
Abstract:
By using the conventional meteorological data, Doppler radar data and NCEP/NCAR reanalysis data, the characteristics of Doppler radar’s reflectivity, environmental condition and trigger mechanism of the heavy rain are analyzed and compared between two abrupt heavy rain processes occurring in Sichuan Basin on 3 July (7.3) and 23 July (7.23) 2011. The results show that: the “7.3” heavy rain happened under a typical circulation background, and moisture transporting to the heavy rain area from the South China Sea was smoothly, thus the heavy rainfall maintained so long, but the “7.23” heavy rain occurred behind the upper cold vortex, and convective unstable energy was abundant and vertical wind shear was strong, thus this heavy rain process happened with hail and thunderstorm weather accompanied, its radar reflectivity was 5 dBz stronger than “7.3” case and had the characteristics of severe storms such as the low level weak reflectivity and the upper echo overhang. As a whole, the non equilibrium force is contributed to the occurrence of heavy rain and it is the excited mechanism of the two heavy rainfalls, and the change of the divergence evolvement is consistent with the strength and the position of the heavy rain which would happen 6 hours later．
By using the conventional meteorological data, Doppler radar data and NCEP/NCAR reanalysis data, the characteristics of Doppler radar’s reflectivity, environmental condition and trigger mechanism of the heavy rain are analyzed and compared between two abrupt heavy rain processes occurring in Sichuan Basin on 3 July (7.3) and 23 July (7.23) 2011. The results show that: the “7.3” heavy rain happened under a typical circulation background, and moisture transporting to the heavy rain area from the South China Sea was smoothly, thus the heavy rainfall maintained so long, but the “7.23” heavy rain occurred behind the upper cold vortex, and convective unstable energy was abundant and vertical wind shear was strong, thus this heavy rain process happened with hail and thunderstorm weather accompanied, its radar reflectivity was 5 dBz stronger than “7.3” case and had the characteristics of severe storms such as the low level weak reflectivity and the upper echo overhang. As a whole, the non equilibrium force is contributed to the occurrence of heavy rain and it is the excited mechanism of the two heavy rainfalls, and the change of the divergence evolvement is consistent with the strength and the position of the heavy rain which would happen 6 hours later．
2006,32(10):64-69, DOI: 10.7519/j.issn.1000-0526.2006.10.010
Abstract:
Based on the data of CINRAD Doppler Radar which located at Xinle of Hebei Province,the hail,strong wind and heavy rainfall weather events in mid-south Hebei in 2004 are statistically analyzed.The routine radar products,such as echo reflectivity,radial velocity,Vertically Integrated Liquid(VIL)Water,hail index,mesocyclone,velocity azimuth display wind profile,etc.are used in this statistics.The results show that hail's VIL value is larger than generic thunder storm's.At the same time,greater VIL value and longer sustaining will bring about greater diameter hail and larger effect area.It is the very useful index to indicate strong wind in mesocyclone products and the wind direction sudden change in radial velocity products.A reference based on analyzing this type synoptic forecast with radar system in future is proposed.
Based on the data of CINRAD Doppler Radar which located at Xinle of Hebei Province,the hail,strong wind and heavy rainfall weather events in mid-south Hebei in 2004 are statistically analyzed.The routine radar products,such as echo reflectivity,radial velocity,Vertically Integrated Liquid(VIL)Water,hail index,mesocyclone,velocity azimuth display wind profile,etc.are used in this statistics.The results show that hail's VIL value is larger than generic thunder storm's.At the same time,greater VIL value and longer sustaining will bring about greater diameter hail and larger effect area.It is the very useful index to indicate strong wind in mesocyclone products and the wind direction sudden change in radial velocity products.A reference based on analyzing this type synoptic forecast with radar system in future is proposed.
Zhou Yuquan, Chen Yingying, Li Juan, Huang Yimei, He Xiaodong, Zhou Feifei, Wu Menxin, Hu Bo, Mao Jietai
2008,34(12):27-35, DOI: 10.7519/j.issn.1000-0526.2008.12.004
Abstract:
Cloud macro and micro physical characteristic parameters play an important role not only in the field of the analysis and forecast of the weather and climate, but also in the field of weather modification to identify the seeding c ondition. Based on the data from FY-2C/D stationary satellite and SBDART radiati on transfer model, associated with the sounding data and surface information, a method retrieving cloud macro and micro physical parameters is established in th is research. These parameters include cloud top height, cloud top temperature, d epth of super-cooled layer, depth of warm layer, cloud bottom height, depth of c loud, cloud optical thickness, cloud effective particle radius and cloud liquid water content. It has been run operationally. In this paper, the correlated info rmation such as physical meaning, retrieving method and technology, retrieving p rocess and data format are simply introduced. Furthermore, comparing with the ob servation of Cloudsat up to the minute, the retrieving results of main cloud par ameters are proved to be reasonable and usable. By contrast with same kind produ cts of MODIS, it also shows good corresponding relationship.
Cloud macro and micro physical characteristic parameters play an important role not only in the field of the analysis and forecast of the weather and climate, but also in the field of weather modification to identify the seeding c ondition. Based on the data from FY-2C/D stationary satellite and SBDART radiati on transfer model, associated with the sounding data and surface information, a method retrieving cloud macro and micro physical parameters is established in th is research. These parameters include cloud top height, cloud top temperature, d epth of super-cooled layer, depth of warm layer, cloud bottom height, depth of c loud, cloud optical thickness, cloud effective particle radius and cloud liquid water content. It has been run operationally. In this paper, the correlated info rmation such as physical meaning, retrieving method and technology, retrieving p rocess and data format are simply introduced. Furthermore, comparing with the ob servation of Cloudsat up to the minute, the retrieving results of main cloud par ameters are proved to be reasonable and usable. By contrast with same kind produ cts of MODIS, it also shows good corresponding relationship.
2013,39(10):1284-1292, DOI: 10.7519/j.issn.1000-0526.2013.10.006
Abstract:
Based on the fog observation data during 24-27 December 2006 (advection radiation fog), NCEP NC reanalysis data (2.5°×2.5°) and GDAS global meteorological data (1°×1°), detailed trajectory analysis of the boundary layer characteristics and water vapor transport of the fog is investigated, combined with the weather condition, meteorological elements and physical quantity field. The results show that: (1) there is thick inversion layer, even multi layer inversion throughout the dense fog event. Temperatures of different inversion tops in the middle and high levels are 2-5℃ higher than the surface temperature. The thickness of inversion layer is more than 200 m, and it gets to 500 m at 08:00 BT 26 December, indicating the atmosphere is very stable and conducive to the convergence of water vapor before the fog forms. However, it is not favorable for the divergence of water vapor after the formation of fog, which helps the development and maintenance of the fog, causing the fog to last about 64 hours with dense fog (visibility <50 m) about 37 hours; (2) The divergence of water vapor flux in low level is negative in the advection fog event. The upper air has persistent moisture convergence and the strongest moisture convergence appears at 02:00 BT 25 December, being -30×10-7 g·s-1·cm-2·hPa-1. The accumulation of low level water vapor makes fog form and develop while the divergence of water vapor flux speeds up its dissipation. 〖JP2〗The long lasting advection radiation fog is mainly caused by the continuous water vapor convergence; (3) The water vapor path is from the coastal area in easten China to Nanjing. The water vapor is continuously supplied from sea during the fog event, with the water vapor flux maximum getting to 2 g·s-1·hPa-1·cm-1. The sufficient supply and supplementary of water vapor determines the duration of the fog.
Based on the fog observation data during 24-27 December 2006 (advection radiation fog), NCEP NC reanalysis data (2.5°×2.5°) and GDAS global meteorological data (1°×1°), detailed trajectory analysis of the boundary layer characteristics and water vapor transport of the fog is investigated, combined with the weather condition, meteorological elements and physical quantity field. The results show that: (1) there is thick inversion layer, even multi layer inversion throughout the dense fog event. Temperatures of different inversion tops in the middle and high levels are 2-5℃ higher than the surface temperature. The thickness of inversion layer is more than 200 m, and it gets to 500 m at 08:00 BT 26 December, indicating the atmosphere is very stable and conducive to the convergence of water vapor before the fog forms. However, it is not favorable for the divergence of water vapor after the formation of fog, which helps the development and maintenance of the fog, causing the fog to last about 64 hours with dense fog (visibility <50 m) about 37 hours; (2) The divergence of water vapor flux in low level is negative in the advection fog event. The upper air has persistent moisture convergence and the strongest moisture convergence appears at 02:00 BT 25 December, being -30×10-7 g·s-1·cm-2·hPa-1. The accumulation of low level water vapor makes fog form and develop while the divergence of water vapor flux speeds up its dissipation. 〖JP2〗The long lasting advection radiation fog is mainly caused by the continuous water vapor convergence; (3) The water vapor path is from the coastal area in easten China to Nanjing. The water vapor is continuously supplied from sea during the fog event, with the water vapor flux maximum getting to 2 g·s-1·hPa-1·cm-1. The sufficient supply and supplementary of water vapor determines the duration of the fog.
2017,43(7):769-780, DOI: 10.7519/j.issn.1000-0526.2017.07.001
Abstract:
The spatial distributions of severe convective wind (SCW) and nonsevere thunderstorms (NT) over South China, occurring between 08:00 BT and 20:00 BT during spring and summer in 2010-2014, were analyzed by using the observational data from China Meteorological Administration. And then, their environmental characteristics were compared between SCW and NT in spring and summer. It was found that SCW in summer is more frequently than that in spring and that NT in summer is about 3.6 times the counts of NT in spring. SCW events mainly concentrate in the western Guangdong to the Pearl River Delta Region. Compared to NT, SCW is generally associated with stronger baroclinity, instability and stronger dynamic forcing. The precipitable water and averaged relative humidity between 700-500 hPa of SCW tend to be higher than those of NT in spring, while the opposite is the case for the pattern in summer. In conclusion, it is obvious that the dynamic forcing for SCW in spring is much better than these in summer, while the thermal condition is more significant in summer.
The spatial distributions of severe convective wind (SCW) and nonsevere thunderstorms (NT) over South China, occurring between 08:00 BT and 20:00 BT during spring and summer in 2010-2014, were analyzed by using the observational data from China Meteorological Administration. And then, their environmental characteristics were compared between SCW and NT in spring and summer. It was found that SCW in summer is more frequently than that in spring and that NT in summer is about 3.6 times the counts of NT in spring. SCW events mainly concentrate in the western Guangdong to the Pearl River Delta Region. Compared to NT, SCW is generally associated with stronger baroclinity, instability and stronger dynamic forcing. The precipitable water and averaged relative humidity between 700-500 hPa of SCW tend to be higher than those of NT in spring, while the opposite is the case for the pattern in summer. In conclusion, it is obvious that the dynamic forcing for SCW in spring is much better than these in summer, while the thermal condition is more significant in summer.
2009,35(1):55-64, DOI: 10.7519/j.issn.1000-0526.2009.1.007
Abstract:
A strong rainstorm is analysis which occurred in Xinghua located the north of Ji angsu province on 25 July 2007. Results show that wind disaster originated from two kinds of rainstorm. One kind was the gust front which occurred at the front of the storm. Strong wind of grade 7-9 was attained when it happened. Another ki nd was the downburst arose in the multi cell storm. The original height of refl ectivity core was higher than -20℃ isotherm. It had the characteristics of conv ergence on the mid level and descending of reflectivity core. The strong wind ab ove grade 10 was attained, when the descending airflow diverged strongly on the ground. A new cell was combined with the former storm above the gust front, thus the storm enhanced. When the downburst happened, the storm weakened, and another new cell was combin ed with the former storm. The downburst happened continuously, and the impact of gust front persisted.
A strong rainstorm is analysis which occurred in Xinghua located the north of Ji angsu province on 25 July 2007. Results show that wind disaster originated from two kinds of rainstorm. One kind was the gust front which occurred at the front of the storm. Strong wind of grade 7-9 was attained when it happened. Another ki nd was the downburst arose in the multi cell storm. The original height of refl ectivity core was higher than -20℃ isotherm. It had the characteristics of conv ergence on the mid level and descending of reflectivity core. The strong wind ab ove grade 10 was attained, when the descending airflow diverged strongly on the ground. A new cell was combined with the former storm above the gust front, thus the storm enhanced. When the downburst happened, the storm weakened, and another new cell was combin ed with the former storm. The downburst happened continuously, and the impact of gust front persisted.
2014,40(2):133-145, DOI: 10.7519/j.issn.1000-0526.2014.02.001
Abstract:
By using the NCEP reanalysis data, the vapor budget of the area covered by the severe torrential rain over the northeast of North China on 21 July, 2012 is calculated according to the vapor budget equation. The results show that meridional water vapor transportation is dominant while the extremely heavy rain hits Beijing Region, where most moist vapor comes from the southern boundary below 500 hPa. The low level regional moisture convergence is consistent with the time and space when the torrential rain breaks out and develops. Above the middle level the vertical vapor transport is more prominent. Then the variation features of the vapor transport corridors and their moisture contributions are got through the HYSPLIT mode. The backward trajectory analyses illustrate two major vapor transport corridors. The moistest vapor derived from Yellow Sea and East China Sea along the low level make the main moisture contribution during the heavy precipitation. Moisture from the South China Sea and the Bay of Bengal strengthens the water vapor in the region when the heavy rain starts and develops. Also the drier vapor corridor along the high level from the northwest of China plays an important role in this case.
By using the NCEP reanalysis data, the vapor budget of the area covered by the severe torrential rain over the northeast of North China on 21 July, 2012 is calculated according to the vapor budget equation. The results show that meridional water vapor transportation is dominant while the extremely heavy rain hits Beijing Region, where most moist vapor comes from the southern boundary below 500 hPa. The low level regional moisture convergence is consistent with the time and space when the torrential rain breaks out and develops. Above the middle level the vertical vapor transport is more prominent. Then the variation features of the vapor transport corridors and their moisture contributions are got through the HYSPLIT mode. The backward trajectory analyses illustrate two major vapor transport corridors. The moistest vapor derived from Yellow Sea and East China Sea along the low level make the main moisture contribution during the heavy precipitation. Moisture from the South China Sea and the Bay of Bengal strengthens the water vapor in the region when the heavy rain starts and develops. Also the drier vapor corridor along the high level from the northwest of China plays an important role in this case.
2012,38(1):1-16, DOI: 10.7519/j.issn.1000-0526.2012.1.001
Abstract:
In this paper, the modulation of atmospheric MJO on typhoon generation over the northwestern Pacific and its mechanism are first studied by using the MJO index. The results show that the MJO plays an important modulation role in typhoon generation over the northwestern Pacific: The proportion of typhoon number is 21 between active period and inactive period; During the MJO active period, the proportion of typhoon number is also 2:1 between phases 5-6 and phases 2-3 of MJO. The composite analyses of atmospheric circulation show that there are different circulation patterns over the northwestern Pacific in different phases of the MJO, which will affect the typhoon generation. In phases 5-6 (2-3), the dynamic factor and convective heating patterns over western Pacific are favorable (unfavorable) for typhoon generation. Then， the comparing analyses of the 30-60 day low frequency kinetic energy in lower and higher levels of the troposphere show that the atmospheric intraseasonal oscillation over the northwestern Pacific has a clear impact on the typhoon generation. There is an evident positive (negative) anomaly area of 30-60 day low frequency kinetic energy in the more (less) typhoon years over the northwestern Pacific east of the Philippines, which means that strong (weak) atmospheric intraseasonal oscillation (ISO) over the northwestern Pacific is favorable (unfavorable) for typhoon generation. The analyses of 200 hPa velocity potential show that there is a clear divergence (convergence) pattern over the northwestern Pacific in the more (less) typhoon years, which is favorable (unfavorable) for typhoon generation. The modulation of the intraseasonal oscillation on the typhoon tracks over the northwestern Pacific is studied by observational data analyses. We classified the main classes of typhoon tracks into 5 types as straight west moving typhoons (I), northwest moving typhoons (II), recurving to Korea/west of Japan typhoons (III), landing on Japan typhoons (IV) and recurving to the east of Japan typhoons (V). Then the composite analyses of atmospheric low-frequency wind fields at 850, 500 and 200 hPa, corresponding to the typhoon forming date, for every typhoon track are completed. The analysis results of relationships between the low-frequency (ISO) wind fields and typhoon tracks have indicated that the typhoon tracks will be affected by wind pattern of the ISO. The low frequency positive vorticity belt (the maximum value line of cyclonic vorticity) associated with low-frequency cyclone (LFC) at 850 hPa is so closely related to the typhoon track, that the maximum value line (belt) of low frequency cyclonic vorticity can be an important factor to predicate the typhoon tracks over the northwestern Pacific. And the typhoon tracks will be also affected by the ISO circulation pattern at 200 hPa, particularly the strong low frequency wind associated with low frequency anticyclone (LFAC).
In this paper, the modulation of atmospheric MJO on typhoon generation over the northwestern Pacific and its mechanism are first studied by using the MJO index. The results show that the MJO plays an important modulation role in typhoon generation over the northwestern Pacific: The proportion of typhoon number is 21 between active period and inactive period; During the MJO active period, the proportion of typhoon number is also 2:1 between phases 5-6 and phases 2-3 of MJO. The composite analyses of atmospheric circulation show that there are different circulation patterns over the northwestern Pacific in different phases of the MJO, which will affect the typhoon generation. In phases 5-6 (2-3), the dynamic factor and convective heating patterns over western Pacific are favorable (unfavorable) for typhoon generation. Then， the comparing analyses of the 30-60 day low frequency kinetic energy in lower and higher levels of the troposphere show that the atmospheric intraseasonal oscillation over the northwestern Pacific has a clear impact on the typhoon generation. There is an evident positive (negative) anomaly area of 30-60 day low frequency kinetic energy in the more (less) typhoon years over the northwestern Pacific east of the Philippines, which means that strong (weak) atmospheric intraseasonal oscillation (ISO) over the northwestern Pacific is favorable (unfavorable) for typhoon generation. The analyses of 200 hPa velocity potential show that there is a clear divergence (convergence) pattern over the northwestern Pacific in the more (less) typhoon years, which is favorable (unfavorable) for typhoon generation. The modulation of the intraseasonal oscillation on the typhoon tracks over the northwestern Pacific is studied by observational data analyses. We classified the main classes of typhoon tracks into 5 types as straight west moving typhoons (I), northwest moving typhoons (II), recurving to Korea/west of Japan typhoons (III), landing on Japan typhoons (IV) and recurving to the east of Japan typhoons (V). Then the composite analyses of atmospheric low-frequency wind fields at 850, 500 and 200 hPa, corresponding to the typhoon forming date, for every typhoon track are completed. The analysis results of relationships between the low-frequency (ISO) wind fields and typhoon tracks have indicated that the typhoon tracks will be affected by wind pattern of the ISO. The low frequency positive vorticity belt (the maximum value line of cyclonic vorticity) associated with low-frequency cyclone (LFC) at 850 hPa is so closely related to the typhoon track, that the maximum value line (belt) of low frequency cyclonic vorticity can be an important factor to predicate the typhoon tracks over the northwestern Pacific. And the typhoon tracks will be also affected by the ISO circulation pattern at 200 hPa, particularly the strong low frequency wind associated with low frequency anticyclone (LFAC).
2011,37(10):1262-1269, DOI: 10.7519/j.issn.1000-0526.2011.10.009
Abstract:
Based on the daily precipitation data at 110 observational stations during 1961-2008 in South China， the climatic characteristics and variation of torrential rain days， rainstorm intensity and contribution which is in annual， the first and second flood seasons in South China were studied by using statistical and diagnostic methods， such as linear regression analysis， Mann Kendall test， wavelet analysis and the computation of trend coefficients. The results have shown that the annual mean torrential rain days have a decreasing trend from coastal regions to inland in South China in recent 48 years， the highest center is in Dongxing of Guangxi （14.9 d）， and the lowest center is in Longlin of Guangxi （3.2 d）. About 72% of the total torrential rain days occurred in the flood seasons with about 45% in the first season and 27% in the second season. The mean torrential rain days have increased faintly in annual， the first and second flood seasons in South China， but it is not obvious. There are the characteristics of interannual and interdecadal changes. The mean rainstorm intensity has increased faintly in annual and in the first flood season in South China. However, since 2005 it has become obviously. The mean rainstorm intensity has declined in the second flood season， but it is not obvious. The annual mean rainstorm contribution to the total rainfall has increased obviously， but the mean contribution is not obvious in the first and second flood seasons. The wavelet analysis has shown that the changes of torrential rain days， intensity and contribution which is in annual， the first and second flood seasons in South China have two significant periods of 2-3 a and 3-4 a.
Based on the daily precipitation data at 110 observational stations during 1961-2008 in South China， the climatic characteristics and variation of torrential rain days， rainstorm intensity and contribution which is in annual， the first and second flood seasons in South China were studied by using statistical and diagnostic methods， such as linear regression analysis， Mann Kendall test， wavelet analysis and the computation of trend coefficients. The results have shown that the annual mean torrential rain days have a decreasing trend from coastal regions to inland in South China in recent 48 years， the highest center is in Dongxing of Guangxi （14.9 d）， and the lowest center is in Longlin of Guangxi （3.2 d）. About 72% of the total torrential rain days occurred in the flood seasons with about 45% in the first season and 27% in the second season. The mean torrential rain days have increased faintly in annual， the first and second flood seasons in South China， but it is not obvious. There are the characteristics of interannual and interdecadal changes. The mean rainstorm intensity has increased faintly in annual and in the first flood season in South China. However, since 2005 it has become obviously. The mean rainstorm intensity has declined in the second flood season， but it is not obvious. The annual mean rainstorm contribution to the total rainfall has increased obviously， but the mean contribution is not obvious in the first and second flood seasons. The wavelet analysis has shown that the changes of torrential rain days， intensity and contribution which is in annual， the first and second flood seasons in South China have two significant periods of 2-3 a and 3-4 a.
2011,37(5):599-606, DOI: 10.7519/j.issn.1000-0526.2011.5.012
Abstract:
Using the diurnal snow data of 120 meteorological stations in Yunnan Province during 1961-2008, the temporal and spatial distribution characteristics and the trend of climatic change of the annual and monthly snow fall are analyzed. It is pointed out that the total trend of snow frequency and covering stations has been decreasing in Yunnan in the recent 50 years. And the annual snow frequency has declined at a mean rate of 4.5 times per year. The temporal trends of monthly snow frequency and covering stations are all negative. Moreover the reduction of snow frequency in December is the largest in magnitude, therefore, it is the most remarkable. And the reduction of snow stations in April is the largest. As far as the spatial change of the secular trend variation of annual snow frequency is concerned, the reduction of annual snow frequency is larger in Northwest Yunnan than in its northeast and east, where the reduction rate is 0.44 times per year. And the temporal changes of annual snowfall and depth of snow cover are studied, the results show that the secular trends of annual snowfall and the maximum depth of snow cover are all positive. This means that in the nearly 50 years the heavy snow frequency has increased over Yunnan Province.
Using the diurnal snow data of 120 meteorological stations in Yunnan Province during 1961-2008, the temporal and spatial distribution characteristics and the trend of climatic change of the annual and monthly snow fall are analyzed. It is pointed out that the total trend of snow frequency and covering stations has been decreasing in Yunnan in the recent 50 years. And the annual snow frequency has declined at a mean rate of 4.5 times per year. The temporal trends of monthly snow frequency and covering stations are all negative. Moreover the reduction of snow frequency in December is the largest in magnitude, therefore, it is the most remarkable. And the reduction of snow stations in April is the largest. As far as the spatial change of the secular trend variation of annual snow frequency is concerned, the reduction of annual snow frequency is larger in Northwest Yunnan than in its northeast and east, where the reduction rate is 0.44 times per year. And the temporal changes of annual snowfall and depth of snow cover are studied, the results show that the secular trends of annual snowfall and the maximum depth of snow cover are all positive. This means that in the nearly 50 years the heavy snow frequency has increased over Yunnan Province.
2014,40(7):816-826, DOI: 10.7519/j.issn.1000-0526.2014.07.005
Abstract:
In term of precipitation data of 2400 stations from 1981 to 2010, annual, seasonal and monthly distribution and evolution characteristics of rainstorm were analyzed. The results show that the processes of rainstorm have been increased evidently since 21 century especially in the south of China, but the duration is relatively short. Rainstorm days have been increased, but the amount of precipitation is not as much as in 1990s. Variation trend of the annual (monthly) precipitation amount is in accordance with that of rainstorm days, but rainfall is averagely more while the rainstorm days are less during spring rainfall phase over the south of Yangtze River. Distribution of the maximum annual rainstorm days is very similar with that of the annual mean rainstorm days, revealing the feature of more in south and east but less in north and west. Maximum annual rainstorm days are more than double of annual average rainstorm days with multi centers due to the effect of topography. The months of maximum monthly rainstorm days over different regions of the same province are incompletely same as the result of the impact of different weather systems. Generally, rainstorm days have been increased since 2000, rainstorm begins earlier, ends latter and lasts longer than before. Nowadays, as the extreme rainfall events and secondary disasters happen frequently, it is conducive for the forecast of quantitative precipitation forecast (QPF) to learn the spatio temporal distribution and evolution features of rainstorm.
In term of precipitation data of 2400 stations from 1981 to 2010, annual, seasonal and monthly distribution and evolution characteristics of rainstorm were analyzed. The results show that the processes of rainstorm have been increased evidently since 21 century especially in the south of China, but the duration is relatively short. Rainstorm days have been increased, but the amount of precipitation is not as much as in 1990s. Variation trend of the annual (monthly) precipitation amount is in accordance with that of rainstorm days, but rainfall is averagely more while the rainstorm days are less during spring rainfall phase over the south of Yangtze River. Distribution of the maximum annual rainstorm days is very similar with that of the annual mean rainstorm days, revealing the feature of more in south and east but less in north and west. Maximum annual rainstorm days are more than double of annual average rainstorm days with multi centers due to the effect of topography. The months of maximum monthly rainstorm days over different regions of the same province are incompletely same as the result of the impact of different weather systems. Generally, rainstorm days have been increased since 2000, rainstorm begins earlier, ends latter and lasts longer than before. Nowadays, as the extreme rainfall events and secondary disasters happen frequently, it is conducive for the forecast of quantitative precipitation forecast (QPF) to learn the spatio temporal distribution and evolution features of rainstorm.
FU Jiaolan, MA Xuekuan, CHEN Tao, ZHANG Fang, ZHANG Xidi, SUN Jun, QUAN Wanqing, YANG Shunan, SHEN Xiaolin
2017,43(5):528-539, DOI: 10.7519/j.issn.1000-0526.2017.05.002
Abstract:
An extremely severe precipitation event took place in North China in 19-20 July 2016. It was characterized by large rainfall, persistent rainfall, warm cloud rainfall, strong local rainfall intensity and orographic precipitation. Its rainfall was larger than that of the extreme rainfall in 3-5 August 1996, and only next to the amount of the 2-7 August 1963 extreme rainfall event. It occurred under the circulation background of the South Asia high moving eastward, the West Pacific subtropical high moving northwestward and the low vortex in the westerlies developing in mid high latitude. The abnormal development of Huanghuai cyclone, southwest and southeast low level jets, and the abnormally abundant moisture indicates that the dynamic lifting and moisture conditions favored this severe rainfall process significantly. The whole rainfall event presented clearly the phase characteristics, and could be divided into two stages. The first stage was the orographic rainfall caused by the easterly winds ahead of the trough from the early morning to the daytime of 19 July, while the second part was produced by spiral rain bands in the north side of Huanghuai cyclone from the night of 19 to the daytime of 20 July. In the first stage, the easterly low level jet was lifted by the Taihang Mountains, which continuously triggered the convective cells along the east edge of the mountains. The weak dry and cold advection at mid level and the strong warm and wet advection at low level jointly maintained the convective instability. The cold pool generated by heavy rainfall and the mesoscale frontogenesis process created by local orographic effect provided favorable conditions for severe convections to occur continuously. The second stage rainfall was mainly related to the development of cut off vortex and Huanghuai cyclone. The blocking of the high pressure system slowed the steps of Huanghuai cyclone in North China, thus leading to the long lasting rainfall process.
An extremely severe precipitation event took place in North China in 19-20 July 2016. It was characterized by large rainfall, persistent rainfall, warm cloud rainfall, strong local rainfall intensity and orographic precipitation. Its rainfall was larger than that of the extreme rainfall in 3-5 August 1996, and only next to the amount of the 2-7 August 1963 extreme rainfall event. It occurred under the circulation background of the South Asia high moving eastward, the West Pacific subtropical high moving northwestward and the low vortex in the westerlies developing in mid high latitude. The abnormal development of Huanghuai cyclone, southwest and southeast low level jets, and the abnormally abundant moisture indicates that the dynamic lifting and moisture conditions favored this severe rainfall process significantly. The whole rainfall event presented clearly the phase characteristics, and could be divided into two stages. The first stage was the orographic rainfall caused by the easterly winds ahead of the trough from the early morning to the daytime of 19 July, while the second part was produced by spiral rain bands in the north side of Huanghuai cyclone from the night of 19 to the daytime of 20 July. In the first stage, the easterly low level jet was lifted by the Taihang Mountains, which continuously triggered the convective cells along the east edge of the mountains. The weak dry and cold advection at mid level and the strong warm and wet advection at low level jointly maintained the convective instability. The cold pool generated by heavy rainfall and the mesoscale frontogenesis process created by local orographic effect provided favorable conditions for severe convections to occur continuously. The second stage rainfall was mainly related to the development of cut off vortex and Huanghuai cyclone. The blocking of the high pressure system slowed the steps of Huanghuai cyclone in North China, thus leading to the long lasting rainfall process.
2007,33(12):116-120, DOI: 10.7519/j.issn.1000-0526.2007.12.018
Abstract:
A comprehensive analysis and process system based on ArcGIS, and its chief targ et, its software frame, standardized data, database system, basic functions and its key technique, etc. are are described. The system is professional especially to weather modification, and it mainly applies to comprehensive analysis and pr ocess for weather modification, decision-making of operation schemes, appraisal of operation effectiveness, and services for enhancement precipitation or suppre ssion hail by ways of cannons or rocks, etc. In this system, information collect ion, analysis, management and comprehensive application of the weather modificat ion are realized. It also can be used in other fields in meteorology.
A comprehensive analysis and process system based on ArcGIS, and its chief targ et, its software frame, standardized data, database system, basic functions and its key technique, etc. are are described. The system is professional especially to weather modification, and it mainly applies to comprehensive analysis and pr ocess for weather modification, decision-making of operation schemes, appraisal of operation effectiveness, and services for enhancement precipitation or suppre ssion hail by ways of cannons or rocks, etc. In this system, information collect ion, analysis, management and comprehensive application of the weather modificat ion are realized. It also can be used in other fields in meteorology.
2010,36(3):9-18, DOI: 10.7519/j.issn.1000-0526.2010.3.002
Abstract:
Potential vorticity (PV) is one of the important concepts in advanced synoptic and dynamic meteorology. This paper is a brief introduction to the theory of potential vorticity, including the concept of PV, the conservation and invertibility of PV, PV thinking, moist PV (MPV), and the application of PV theory.
Potential vorticity (PV) is one of the important concepts in advanced synoptic and dynamic meteorology. This paper is a brief introduction to the theory of potential vorticity, including the concept of PV, the conservation and invertibility of PV, PV thinking, moist PV (MPV), and the application of PV theory.
2013,39(9):1163-1170, DOI: 10.7519/j.issn.1000-0526.2013.09.011
Abstract:
Drought and flood have significant impacts on catchment water use and ecological balance. To develop practical drought/flood monitoring indicators that only need a few climate variables, it is fundamentally necessary to explore the relationship between hydrology variables and climate variables for the specific catchment. This study investigates the correlations between lake water level and various time scale climatological indices according to the standardized precipitation index (SPI) and the standardized precipitation evapotranspiration index (SPEI), based on the monthly water level records from Honghu Lake representative gauging stations and the monthly observations of 8 meteorological stations in the Four Lake Basin. The results showed that extreme droughts and floods are primarily controlled by precipitation variability over the Four Lake Basin, and both SPEI and SPI are well related with lake water level of Honghu Lake while the degree of the correlation varies between different seasons and SPEI/SPI time scales, with the highest correlations for rainy summer and autumn months. Generally, the 4-6 month scale SPEI/SPI drought index is most closely correlated with lake water level of Honghu Lake, showing an apparent response of lake water level to the current and former months’ water surplus and deficiency. When compared with the historical time series of monthly average lake water level of Honghu Lake, the 5 month scale SPEI/SPI agrees well with the variability of the lake water level. The response relationship found during the study can not only aid the monitoring and forecasting of flood and drought conditions in the Four Lake Basin based on conventional weather data, but also provides some references for other places of China.
Drought and flood have significant impacts on catchment water use and ecological balance. To develop practical drought/flood monitoring indicators that only need a few climate variables, it is fundamentally necessary to explore the relationship between hydrology variables and climate variables for the specific catchment. This study investigates the correlations between lake water level and various time scale climatological indices according to the standardized precipitation index (SPI) and the standardized precipitation evapotranspiration index (SPEI), based on the monthly water level records from Honghu Lake representative gauging stations and the monthly observations of 8 meteorological stations in the Four Lake Basin. The results showed that extreme droughts and floods are primarily controlled by precipitation variability over the Four Lake Basin, and both SPEI and SPI are well related with lake water level of Honghu Lake while the degree of the correlation varies between different seasons and SPEI/SPI time scales, with the highest correlations for rainy summer and autumn months. Generally, the 4-6 month scale SPEI/SPI drought index is most closely correlated with lake water level of Honghu Lake, showing an apparent response of lake water level to the current and former months’ water surplus and deficiency. When compared with the historical time series of monthly average lake water level of Honghu Lake, the 5 month scale SPEI/SPI agrees well with the variability of the lake water level. The response relationship found during the study can not only aid the monitoring and forecasting of flood and drought conditions in the Four Lake Basin based on conventional weather data, but also provides some references for other places of China.
2011,37(1):122-128, DOI: 10.7519/j.issn.1000-0526.2011.1.017
Abstract:
The following are the main characteristics of the general atmospheric circulation in October 2010. There were two polar vortex centers in the Northern Hemisphere. The circulation presents a four wave pattern in middle high latitudes, in which the strong Ural ridge corresponds to a large 40 gpm positive anomaly area. Strength of the Western Pacific subtropical high is weaker than normal years. The monthly mean temperature (10.1 ℃) is 0.5 ℃ higher than the same period of normal years, and the mean precipitation (42.6 mm) is 15.1% above normal. The major weather events include: 8 precipitation processes occuring, in which a rare heavy rain has struck on Hainan in the first and middle dekad of October; two tropical cyclones generated, with one super typhoon (Chaba, numbered 1013) landed in Fujian; in the last dekad of October, strong cold air outbreak across most areas of China; heavy fog aroused in the central and eastern China.
The following are the main characteristics of the general atmospheric circulation in October 2010. There were two polar vortex centers in the Northern Hemisphere. The circulation presents a four wave pattern in middle high latitudes, in which the strong Ural ridge corresponds to a large 40 gpm positive anomaly area. Strength of the Western Pacific subtropical high is weaker than normal years. The monthly mean temperature (10.1 ℃) is 0.5 ℃ higher than the same period of normal years, and the mean precipitation (42.6 mm) is 15.1% above normal. The major weather events include: 8 precipitation processes occuring, in which a rare heavy rain has struck on Hainan in the first and middle dekad of October; two tropical cyclones generated, with one super typhoon (Chaba, numbered 1013) landed in Fujian; in the last dekad of October, strong cold air outbreak across most areas of China; heavy fog aroused in the central and eastern China.
2013,39(3):281-290, DOI: 10.7519/j.issn.1000-0526.2013.03.002
Abstract:
By using conventional observation data and NCEP reanalysis data, diagnostic analysis is performed on a rainstorm process, which occurred on 22-25 July 2010 in the western part of Sichuan Basin. The result shows that the rainstorm was generated under the circulation background that low level southerly airflows had remained over the region from the South China Sea to Sichuan Basin, so this rainstorm was closely related to the evolution of the southerly wind speeds. The rainfall intensity increased as the south winds grew stronger. Speed convergence formed by the enhanced south winds and positive vorticity advections became main dynamic trigger factors for the rainstorm. Therefore, the rainstorm is pretty consistent with the low level convergence and the positive vorticity advection. In addition, the result of WRF numerical simulation further indicates that: the evolution of 3 h wind speed at 850 hPa has good indication for the development of mesoscale convective systems. On the leeward side of the 3 h wind speed increasing area, convective cloud clusters are to develop rapidly in the next 3 hours. Moreover, the topographic influence simulation tests suggest that the airflow convergence generated in the west of the Basin is closely related to the topography of plateau.
By using conventional observation data and NCEP reanalysis data, diagnostic analysis is performed on a rainstorm process, which occurred on 22-25 July 2010 in the western part of Sichuan Basin. The result shows that the rainstorm was generated under the circulation background that low level southerly airflows had remained over the region from the South China Sea to Sichuan Basin, so this rainstorm was closely related to the evolution of the southerly wind speeds. The rainfall intensity increased as the south winds grew stronger. Speed convergence formed by the enhanced south winds and positive vorticity advections became main dynamic trigger factors for the rainstorm. Therefore, the rainstorm is pretty consistent with the low level convergence and the positive vorticity advection. In addition, the result of WRF numerical simulation further indicates that: the evolution of 3 h wind speed at 850 hPa has good indication for the development of mesoscale convective systems. On the leeward side of the 3 h wind speed increasing area, convective cloud clusters are to develop rapidly in the next 3 hours. Moreover, the topographic influence simulation tests suggest that the airflow convergence generated in the west of the Basin is closely related to the topography of plateau.
2011,37(2):142-155, DOI: 10.7519/j.issn.1000-0526.2011.2.003
Abstract:
Using the Variational Doppler Radar Analysis System (VDRAS) combined with local unconventional observation data, a more in depth contrastive analysis is carried on the initiation mechanism of two storm cases in Beijing, one is 814 (August 14, 2008) case with strong rainfall that we call it as moist storm and the other is 824 (August 24, 2008) case with little rainfall that we call it as dry storm. The results show: (1) The synoptic scale systems of 814 storm were stable Northeast cold vortex low trough at 500 hPa and shear line at 850 hPa, the specific humidity that more than 12 g·kg-1 below 850 hPa and the relative humidity that more than 90% in the surface indicated that the atmosphere was very moist. It had convective instability caused by humidity advection in lower levels. The 824 storm had a prevailing straight west wind in high levels, an anticyclone in lower levels, and a surface cold front moving fast.The specific humidity that less than 6 g·kg-1, and the relative humidity that less than 30% below 850 hPa indicated that the atmosphere was very dry. It had convective instability caused by temperature advection. (2) There was much strong vertical wind shear in the whole vertical layer for 814 storm case, the clockwise wind direction with height within 500-1500 m intensified the warm and humidity inflow of lower layer advantageous to storm initiation and development. While there was weak vertical wind shear and unobvious warm and humidity inflow of lower layer for 824 case, which was not conducive to storm initiation and development. In addition, composited wind of the whole troposphere and storm movement speed were very low for 814 case, but they were very high for 824 case. (3) The 814 storm was formed by the collision and mergence of multi cell storms, a convergence line was formed by the cold pool outflow produced by the precipitation of the upstream of thunderstorm cell and the east wind in low levels which forced the low level warm and moist air to uplift, additionally the strong convective instability and vertical wind shear supported the formation and development of new storm. The interactions (collisions) of gust fronts in the leading edge of cold pool of multi cell thunderstorm group, further exacerbating the low level instability, leading to the regeneration and mergence of new convective thunderstorms. The 824 storm was a line convective system accompanied with cold front that rapid moved eastward and lasted for short time, there was no east wind with warm and moisture air accompanying the cold pool outflow produced by the downdrafts of thunderstorm. The absence of mesoscale lifting mechanism and moisture inflow couldn’t support the formation and development of new storm.
Using the Variational Doppler Radar Analysis System (VDRAS) combined with local unconventional observation data, a more in depth contrastive analysis is carried on the initiation mechanism of two storm cases in Beijing, one is 814 (August 14, 2008) case with strong rainfall that we call it as moist storm and the other is 824 (August 24, 2008) case with little rainfall that we call it as dry storm. The results show: (1) The synoptic scale systems of 814 storm were stable Northeast cold vortex low trough at 500 hPa and shear line at 850 hPa, the specific humidity that more than 12 g·kg-1 below 850 hPa and the relative humidity that more than 90% in the surface indicated that the atmosphere was very moist. It had convective instability caused by humidity advection in lower levels. The 824 storm had a prevailing straight west wind in high levels, an anticyclone in lower levels, and a surface cold front moving fast.The specific humidity that less than 6 g·kg-1, and the relative humidity that less than 30% below 850 hPa indicated that the atmosphere was very dry. It had convective instability caused by temperature advection. (2) There was much strong vertical wind shear in the whole vertical layer for 814 storm case, the clockwise wind direction with height within 500-1500 m intensified the warm and humidity inflow of lower layer advantageous to storm initiation and development. While there was weak vertical wind shear and unobvious warm and humidity inflow of lower layer for 824 case, which was not conducive to storm initiation and development. In addition, composited wind of the whole troposphere and storm movement speed were very low for 814 case, but they were very high for 824 case. (3) The 814 storm was formed by the collision and mergence of multi cell storms, a convergence line was formed by the cold pool outflow produced by the precipitation of the upstream of thunderstorm cell and the east wind in low levels which forced the low level warm and moist air to uplift, additionally the strong convective instability and vertical wind shear supported the formation and development of new storm. The interactions (collisions) of gust fronts in the leading edge of cold pool of multi cell thunderstorm group, further exacerbating the low level instability, leading to the regeneration and mergence of new convective thunderstorms. The 824 storm was a line convective system accompanied with cold front that rapid moved eastward and lasted for short time, there was no east wind with warm and moisture air accompanying the cold pool outflow produced by the downdrafts of thunderstorm. The absence of mesoscale lifting mechanism and moisture inflow couldn’t support the formation and development of new storm.
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