ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Volume 47,Issue 1,2021 Table of Contents
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.
7 Analysis on Characteristics of Particle Size Distribution During Rain and Snow Processes in Hohhot
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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ISSN:1000-0526 CN:11-2282/P