ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Volume 42,Issue 8,2016 Table of Contents
2016, 42(8):905-919.
DOI: 10.7519/j.issn.1000-0526.2016.08.001
Abstract:
In this paper, FY2E satellite data, Doppler radar products and 4Dvar assimilation data, regional automatic station data, conventional meteorological data and NCEP reanalysis data are used to analyze the organizational structure, evolution and formation mechanism of rainstorm cloud clusters over the north Huanghuai Region on 13 August 2010. The results indicate that the cloud clusters developed under the synoptic situation of lowvortex and shear. The southwest jet, lowvortex shear line and cold air were the main weather systems. The clusters’ ambient characteristics included high instable convective energy, strong lowlevel vertical wind shear and sufficient moisture. MβCSs, which induced heavy rainfall during the early period, had different forming mechanisms. With the development of lowvortex, several MβCSs merged into a round MαCS. The force of warm moisture airflow in low level and convergence line on surface were the main mechanism of the round MαCS. γ or β mesoscale cyclone and convergence line created the dynamic triggering effects. Enhancement and extension backward of convergence area led to the self and backward development of MCS. Strong outflow at the back of convective cell during the mature stage caused the cells to break, and convergence of southwest airflow and south airflow on the edge of the cyclone circulation made the combination of convective cells. The linear convective systems that developed during the mature and decline phase of MαCS showed obvious characteristics of heavy rainfall.
In this paper, FY2E satellite data, Doppler radar products and 4Dvar assimilation data, regional automatic station data, conventional meteorological data and NCEP reanalysis data are used to analyze the organizational structure, evolution and formation mechanism of rainstorm cloud clusters over the north Huanghuai Region on 13 August 2010. The results indicate that the cloud clusters developed under the synoptic situation of lowvortex and shear. The southwest jet, lowvortex shear line and cold air were the main weather systems. The clusters’ ambient characteristics included high instable convective energy, strong lowlevel vertical wind shear and sufficient moisture. MβCSs, which induced heavy rainfall during the early period, had different forming mechanisms. With the development of lowvortex, several MβCSs merged into a round MαCS. The force of warm moisture airflow in low level and convergence line on surface were the main mechanism of the round MαCS. γ or β mesoscale cyclone and convergence line created the dynamic triggering effects. Enhancement and extension backward of convergence area led to the self and backward development of MCS. Strong outflow at the back of convective cell during the mature stage caused the cells to break, and convergence of southwest airflow and south airflow on the edge of the cyclone circulation made the combination of convective cells. The linear convective systems that developed during the mature and decline phase of MαCS showed obvious characteristics of heavy rainfall.
2016, 42(8):920-933.
DOI: 10.7519/j.issn.1000-0526.2016.08.002
Abstract:
To further explore the formation and development of hail cloud in Guizhou Region and the transformation mechanism of microphysical conditions during the growing process of hail, 12 hail cases during 2012-2015 are studied through numerical simulation using threedimensional hail cloud model. The results show that: all kinds of water into the spatial distribution of hail is the material basis of the hail growth, and rising air and water vapor phase change with a positive feedback effect. The hail particles grow mainly taking graupel particles as embryo, and growth mode is given priority to sleet automatic conversion. In the process of continuous development of hail, hail cloud at the end of the first developing process, there is still 0℃ layer with 4 km or lower thickness which is the thermal environmental condition for the development of hail cloud again. In the hail area the surface airflow are divergent, leading to the formation of stronger updraft convergence on both sides, which is dynamic conditions for the development of hail cloud again. At the same time, the air convergence makes the water vapor the original hail air continuously flow into the air convergence zone on both sides, which becomes water vapor source of the hail cloud development. The rapid increase of ice crystals and graupel particles in the hail cloud provides favorable microphysical material conditions for the growth of hail again.
To further explore the formation and development of hail cloud in Guizhou Region and the transformation mechanism of microphysical conditions during the growing process of hail, 12 hail cases during 2012-2015 are studied through numerical simulation using threedimensional hail cloud model. The results show that: all kinds of water into the spatial distribution of hail is the material basis of the hail growth, and rising air and water vapor phase change with a positive feedback effect. The hail particles grow mainly taking graupel particles as embryo, and growth mode is given priority to sleet automatic conversion. In the process of continuous development of hail, hail cloud at the end of the first developing process, there is still 0℃ layer with 4 km or lower thickness which is the thermal environmental condition for the development of hail cloud again. In the hail area the surface airflow are divergent, leading to the formation of stronger updraft convergence on both sides, which is dynamic conditions for the development of hail cloud again. At the same time, the air convergence makes the water vapor the original hail air continuously flow into the air convergence zone on both sides, which becomes water vapor source of the hail cloud development. The rapid increase of ice crystals and graupel particles in the hail cloud provides favorable microphysical material conditions for the growth of hail again.
2016, 42(8):934-943.
DOI: 10.7519/j.issn.1000-0526.2016.08.003
Abstract:
Using daily rainfall data of Xisha Islands, reanalysis data of European Centre for MediumRange Weather Forecasts (ECMWF), typhoon data of Shanghai Typhoon Institute, the present study investigates the rainfall climatology of Xisha, and classifies its synoptic situation associated with the nonTC heavy precipitation for September-October. The method used is a new composite method, which combines REOF and Kmeans clustering. It is found that Xisha is dry from December to April of the following year, and wet from May to November. Monthly rainfall peaks at September and October. Three optimal categories are obtained, featuring southwest monsoon trough, the combined effect of the monsoon trough and cold, strong cold air, respectively. Among the three categories, the first one occurred mainly in September of the 1990s, while the third one, which appears mainly in October, has increased significantly since 1990s. Preliminary analysis shows that the monsoon trough was more active in 1990s and the cold air activities have become stronger since 1990s. This may be the major reason for the increasing of the total amount of the nonTC heavy rainfall.
Using daily rainfall data of Xisha Islands, reanalysis data of European Centre for MediumRange Weather Forecasts (ECMWF), typhoon data of Shanghai Typhoon Institute, the present study investigates the rainfall climatology of Xisha, and classifies its synoptic situation associated with the nonTC heavy precipitation for September-October. The method used is a new composite method, which combines REOF and Kmeans clustering. It is found that Xisha is dry from December to April of the following year, and wet from May to November. Monthly rainfall peaks at September and October. Three optimal categories are obtained, featuring southwest monsoon trough, the combined effect of the monsoon trough and cold, strong cold air, respectively. Among the three categories, the first one occurred mainly in September of the 1990s, while the third one, which appears mainly in October, has increased significantly since 1990s. Preliminary analysis shows that the monsoon trough was more active in 1990s and the cold air activities have become stronger since 1990s. This may be the major reason for the increasing of the total amount of the nonTC heavy rainfall.
2016, 42(8):944-953.
DOI: 10.7519/j.issn.1000-0526.2016.08.004
Abstract:
In order to compare different effects on simulations of heavy fog processes under various microphysics， planetary boundary layer and land surface schemes， 21 heavy fog events selected from the observation data of expressway weather monitoring system from 2011 to 2013 were simulated using WRF (Weather Research and Forecasting Model). Influence of different parameterization schemes on simulating these fog events was discussed and the forecasting indexes of fog formation based on the output physical variables of WRF were determined. The results are as follows： （1） The simulation of the whole fog occurring processes is the best when selecting WDM6 scheme as the microphysics scheme， QNSE scheme as the planetary boundary layer scheme and the SLAB scheme as the land surface scheme considering the effects of different parameterization schemes in simulating the nearsurface meteorological factors， the air temperature in the upperlevel atmosphere and the distribution of fog areas comprehensively. （2） Under the optimum configure of the parameterization schemes and giving consideration to the limited computing resources of the meteorological professional departments in China and the suitable vertical resolution of the model，the analysis on the numerical simulation results of atmospheric backgrounds during the 21 heavy fog events demonstrates that the forecasting indexes of heavy fog on the expressway of Jiangsu Province are that liquid water content at lowest model level (30-40 m) is more than 0.015 g·kg-1， or 2 m relative humidity is more than 95% and 10 m wind speed is less than 3 m·s-1 at the same time.
In order to compare different effects on simulations of heavy fog processes under various microphysics， planetary boundary layer and land surface schemes， 21 heavy fog events selected from the observation data of expressway weather monitoring system from 2011 to 2013 were simulated using WRF (Weather Research and Forecasting Model). Influence of different parameterization schemes on simulating these fog events was discussed and the forecasting indexes of fog formation based on the output physical variables of WRF were determined. The results are as follows： （1） The simulation of the whole fog occurring processes is the best when selecting WDM6 scheme as the microphysics scheme， QNSE scheme as the planetary boundary layer scheme and the SLAB scheme as the land surface scheme considering the effects of different parameterization schemes in simulating the nearsurface meteorological factors， the air temperature in the upperlevel atmosphere and the distribution of fog areas comprehensively. （2） Under the optimum configure of the parameterization schemes and giving consideration to the limited computing resources of the meteorological professional departments in China and the suitable vertical resolution of the model，the analysis on the numerical simulation results of atmospheric backgrounds during the 21 heavy fog events demonstrates that the forecasting indexes of heavy fog on the expressway of Jiangsu Province are that liquid water content at lowest model level (30-40 m) is more than 0.015 g·kg-1， or 2 m relative humidity is more than 95% and 10 m wind speed is less than 3 m·s-1 at the same time.
2016, 42(8):954-961.
DOI: 10.7519/j.issn.1000-0526.2016.08.005
Abstract:
The PM2.5 mass concentration data from Baolian Atmospheric Composition Monitoring Station, which represents urban area, in 2005-2014 and the data from Shangdianzi BAPStation, which represents rural area, from 2006 to 2014 are used to analyze its longterm temporal evolvement in Beijing. The results show that the PM2.5 pollution was the severest during 2005-2007. Since 2008, the annual mean mass concentration and the days of moderate pollution or over have been reduced, but the situation became worse from 2013 to 2014. The average mass concentration in urban area was the highest in winter and autumn, and took the second place from spring to the early of summer. However, in recent several years, such pollution tends to be reduced somewhat in spring and summer. At the same time, high mass concentration was found more often in autumn, which enlarges the seasonal gap. One impact factor is the sanddust weather in spring. At Shangdianzi Station, the rural area, the annual mean mass concentration is higher in spring and summer, different from that in urban area. But since 2011, the above difference has become much smaller. This indicates that the regional pollution takes place more commonly. On average, there are 30 pollution days at moderate level, 26 days at severe level and 4.7 days at extreme level every year. However, there is some monthly and annual discrepancies of this characteristic. Besides, the moderate pollution cases decreased while severe ones increased in 2013 and 2014. Therefore, the annual mean mass concentration has higher relationship with the severe pollution events in winter and autumn. The moderate or severe pollution days in Shangdianzi are only 1/3 of that in urban area. Moreover, the persistent pollution event appears in winter and autumn normally. The annual average times of pollution events which last at least 3 days are 1.9 for moderate level and 0.6 for severe level during 2008-2014. Most extreme events could cover 2 to 3 days only. Based on the statistics, the mass concentration often reaches severe grade or above after the middle stage of the event. So, it might reduce the possibility of severe pollution by controlling emission in advance when the meteorological condition is not favorable for the diffusion of pollutants.
The PM2.5 mass concentration data from Baolian Atmospheric Composition Monitoring Station, which represents urban area, in 2005-2014 and the data from Shangdianzi BAPStation, which represents rural area, from 2006 to 2014 are used to analyze its longterm temporal evolvement in Beijing. The results show that the PM2.5 pollution was the severest during 2005-2007. Since 2008, the annual mean mass concentration and the days of moderate pollution or over have been reduced, but the situation became worse from 2013 to 2014. The average mass concentration in urban area was the highest in winter and autumn, and took the second place from spring to the early of summer. However, in recent several years, such pollution tends to be reduced somewhat in spring and summer. At the same time, high mass concentration was found more often in autumn, which enlarges the seasonal gap. One impact factor is the sanddust weather in spring. At Shangdianzi Station, the rural area, the annual mean mass concentration is higher in spring and summer, different from that in urban area. But since 2011, the above difference has become much smaller. This indicates that the regional pollution takes place more commonly. On average, there are 30 pollution days at moderate level, 26 days at severe level and 4.7 days at extreme level every year. However, there is some monthly and annual discrepancies of this characteristic. Besides, the moderate pollution cases decreased while severe ones increased in 2013 and 2014. Therefore, the annual mean mass concentration has higher relationship with the severe pollution events in winter and autumn. The moderate or severe pollution days in Shangdianzi are only 1/3 of that in urban area. Moreover, the persistent pollution event appears in winter and autumn normally. The annual average times of pollution events which last at least 3 days are 1.9 for moderate level and 0.6 for severe level during 2008-2014. Most extreme events could cover 2 to 3 days only. Based on the statistics, the mass concentration often reaches severe grade or above after the middle stage of the event. So, it might reduce the possibility of severe pollution by controlling emission in advance when the meteorological condition is not favorable for the diffusion of pollutants.
2016, 42(8):962-970.
DOI: 10.7519/j.issn.1000-0526.2016.08.006
Abstract:
The horizontal wind observations from seven boundary layer profilers in Shanghai are evaluated by using the analysis data from the NCEP Global Data Assimilation System (GDAS) in June 2014. Since the denselyobserved rawinsonde data in Shanghai has not been assimilated by GDAS, these data are used to evaluate the accuracy and representativeness of NCEP’s analysis data. The results show that both bias and RMSE between rawinsonde observations and NCEP data are small, which indicates that NCEP’s analysis data are accurate enough to evaluate the quality of profiler data in Shanghai. Then the profiler observations are further compared with NCEP’s analysis data. The bias and RMSE are respectively -0.14 m·s-1 and 2.72 m·s-1 for wind speed, and -4.28° is for wind direction over all heights for the whole month. The comparison shows that data quality of wind profiler in Shanghai is close to that of rawinsonde. The wind profiler observation data in the network are reliable and can be used in operation or research.
The horizontal wind observations from seven boundary layer profilers in Shanghai are evaluated by using the analysis data from the NCEP Global Data Assimilation System (GDAS) in June 2014. Since the denselyobserved rawinsonde data in Shanghai has not been assimilated by GDAS, these data are used to evaluate the accuracy and representativeness of NCEP’s analysis data. The results show that both bias and RMSE between rawinsonde observations and NCEP data are small, which indicates that NCEP’s analysis data are accurate enough to evaluate the quality of profiler data in Shanghai. Then the profiler observations are further compared with NCEP’s analysis data. The bias and RMSE are respectively -0.14 m·s-1 and 2.72 m·s-1 for wind speed, and -4.28° is for wind direction over all heights for the whole month. The comparison shows that data quality of wind profiler in Shanghai is close to that of rawinsonde. The wind profiler observation data in the network are reliable and can be used in operation or research.
2016, 42(8):971-979.
DOI: 10.7519/j.issn.1000-0526.2016.08.007
Abstract:
An applicable method to retrieve cloud top height (CTH) is proposed. Using the ATrain data in 2007, CTH in low latitude area (15°S~15°N) is retrieved. Firstly, using the brightness temperatures at Channels 31 and 32 of MODIS, clouds are classified into three categories including opaque clouds, semitransparent clouds and transparent clouds based on SVM method with 90.6% accuracy. Then, the CTH of the three categories are retrieved by kernel regression.The root mean square errors (RMSE) are 0.95 km, 1.17 km and 1.27 km, respectively, compared with CloudSat 2BGEOPROFLIDAR product.The errors of the three categories of clouds all decrease after being classified. Lastly, three typical cases are analyzed. The algorithm could be carried out in other satellites containing infrared split window channels.
An applicable method to retrieve cloud top height (CTH) is proposed. Using the ATrain data in 2007, CTH in low latitude area (15°S~15°N) is retrieved. Firstly, using the brightness temperatures at Channels 31 and 32 of MODIS, clouds are classified into three categories including opaque clouds, semitransparent clouds and transparent clouds based on SVM method with 90.6% accuracy. Then, the CTH of the three categories are retrieved by kernel regression.The root mean square errors (RMSE) are 0.95 km, 1.17 km and 1.27 km, respectively, compared with CloudSat 2BGEOPROFLIDAR product.The errors of the three categories of clouds all decrease after being classified. Lastly, three typical cases are analyzed. The algorithm could be carried out in other satellites containing infrared split window channels.
2016, 42(8):980-986.
DOI: 10.7519/j.issn.1000-0526.2016.08.008
Abstract:
Using the data of surface observation, cloud classification and blackbody temperature from 1 April 2012 to 31 July 2013 and according to different weather types, this paper states the background, analyzes the cases and discusses the relationship among cloud classification of satellite data, TBB products, weather phenomena and cloudy shapes. The results show that after cancelling surface cloudy observation, we can carry out the cloud observing operation based on cloud classification and correct the errors by combining TBB and weather phenomena. When TBB<240 K and variability is close to zero in the course of changing from negative to positive value, thunderstorms are always prone to occur and the cloudy shape is cumulonimbus cloud. When TBB is between 240 K and 260 K, there will be stable precipitation and cloudy shape is stratocumulus or altocumulus.
Using the data of surface observation, cloud classification and blackbody temperature from 1 April 2012 to 31 July 2013 and according to different weather types, this paper states the background, analyzes the cases and discusses the relationship among cloud classification of satellite data, TBB products, weather phenomena and cloudy shapes. The results show that after cancelling surface cloudy observation, we can carry out the cloud observing operation based on cloud classification and correct the errors by combining TBB and weather phenomena. When TBB<240 K and variability is close to zero in the course of changing from negative to positive value, thunderstorms are always prone to occur and the cloudy shape is cumulonimbus cloud. When TBB is between 240 K and 260 K, there will be stable precipitation and cloudy shape is stratocumulus or altocumulus.
2016, 42(8):987-995.
DOI: 10.7519/j.issn.1000-0526.2016.08.009
Abstract:
Divergence and temperature advection can be used to infer the atmospheric vertical movement situation and the stability of atmospheric stratification respectively, which is helpful to deduce the precipitation evolution trend. Considering there is no vertical divergence profile and vertical temperature advection profile products of China new generation weather radar, this paper proposes the retrieval algorithms of vertical divergence and temperature advection profiles from Doppler weather radar data. First, the vertical wind profile and vertical divergence profile above the radar station are retrieved using layered VVP method from radar radial velocity data， and then under the assumption that the atmosphere were in the geostrophic balance in middle latitude and based on the relationship between the temperature advection and geostrophic wind changing with height, the vertical temperature advection profile is retrieved from the vertical wind profile. Taking two severe precipitation processes as examples, the retrieved vertical wind profile, vertical divergence profile and vertical temperature advection profile are analyzed. The results show that the vertical wind profile and vertical divergence profile can be retrieved reasonably using layered VVP in the case of largescale precipitation around radar. In this case, the retrieved winds represent average winds within the valid detection range of radar, which meets approximately the geostrophic equilibrium condition, so the vertical temperature advection profile can be retrieved reasonably from the vertical wind profile. The synoptic principles and the observation data can be used to explain the reliability of the retrieval results.
Divergence and temperature advection can be used to infer the atmospheric vertical movement situation and the stability of atmospheric stratification respectively, which is helpful to deduce the precipitation evolution trend. Considering there is no vertical divergence profile and vertical temperature advection profile products of China new generation weather radar, this paper proposes the retrieval algorithms of vertical divergence and temperature advection profiles from Doppler weather radar data. First, the vertical wind profile and vertical divergence profile above the radar station are retrieved using layered VVP method from radar radial velocity data， and then under the assumption that the atmosphere were in the geostrophic balance in middle latitude and based on the relationship between the temperature advection and geostrophic wind changing with height, the vertical temperature advection profile is retrieved from the vertical wind profile. Taking two severe precipitation processes as examples, the retrieved vertical wind profile, vertical divergence profile and vertical temperature advection profile are analyzed. The results show that the vertical wind profile and vertical divergence profile can be retrieved reasonably using layered VVP in the case of largescale precipitation around radar. In this case, the retrieved winds represent average winds within the valid detection range of radar, which meets approximately the geostrophic equilibrium condition, so the vertical temperature advection profile can be retrieved reasonably from the vertical wind profile. The synoptic principles and the observation data can be used to explain the reliability of the retrieval results.
2016, 42(8):996-1006.
DOI: 10.7519/j.issn.1000-0526.2016.08.010
Abstract:
According to daily observation of four 100 m meteorological towers in Urumqi from June 2013 to April 2014 by 10 min meteorological data, this paper analyzes the A-F atmospheric stability applicability of the temperature difference method, temperature differencewind speed method, wind ratio method, Richard method, and Overall Richardson number method. It is found that the temperature differencewind speed method is more suitable for the classification of Urumqi City atmospheric stability. Using this method, we calculate the A-F stability and, further, conduct statistical analysis of the frequency distribution characteristics of Urumqi City and suburban stability. The results show that the frequency of stable condition is higher in suburbs than in urban area and the frequency of neutral condition is higher in urban than in suburb, and the frequency of unstable conditions is higher in southern suburbs and urban than in northern suburbs. The frequency of neutral condition is the highest in winter but the lowest in spring and autumn. The frequency of unstable condition is the highest in June but lowest in September and January. The frequency of stable condition is the highest in October and January but lowest in June and July. The proportion of the unstable is the maximum (88.3%-96.3% of all day) during daytime in summer, but minimum (51.3%-60%) in winter. The daily variation of unstable condition is in inverse of neutral and stable conditions. The frequency of stable condition is the highest at sunrise moment in suburb and 2 hours after sunrise in urban. The neutral condition at sunrise and 1-3 hours after sunset respectively reach their two peaks. The frequency of stable condition is higher in cold weather than in hot weather, and it is higher in calm weather than in windy weather in suburb, and the frequency of unstable condition is higher in rain weather than in heavy snow weather. The frequency of neutral and stable conditions are the highest before blowing sand but the unstable condition is the highest during and after sand blowing. The high frequency of atmospheric stability is in B, C and F category in spring and summer; the frequency of C and F category in summer in south suburbs and north suburbs is about 45%. The high frequency of atmospheric stability is B and E category in autumn (about 40%-50%). The high frequency of atmospheric stability is D category in urban, while is F category in south suburbs, north suburbs and north rural.
According to daily observation of four 100 m meteorological towers in Urumqi from June 2013 to April 2014 by 10 min meteorological data, this paper analyzes the A-F atmospheric stability applicability of the temperature difference method, temperature differencewind speed method, wind ratio method, Richard method, and Overall Richardson number method. It is found that the temperature differencewind speed method is more suitable for the classification of Urumqi City atmospheric stability. Using this method, we calculate the A-F stability and, further, conduct statistical analysis of the frequency distribution characteristics of Urumqi City and suburban stability. The results show that the frequency of stable condition is higher in suburbs than in urban area and the frequency of neutral condition is higher in urban than in suburb, and the frequency of unstable conditions is higher in southern suburbs and urban than in northern suburbs. The frequency of neutral condition is the highest in winter but the lowest in spring and autumn. The frequency of unstable condition is the highest in June but lowest in September and January. The frequency of stable condition is the highest in October and January but lowest in June and July. The proportion of the unstable is the maximum (88.3%-96.3% of all day) during daytime in summer, but minimum (51.3%-60%) in winter. The daily variation of unstable condition is in inverse of neutral and stable conditions. The frequency of stable condition is the highest at sunrise moment in suburb and 2 hours after sunrise in urban. The neutral condition at sunrise and 1-3 hours after sunset respectively reach their two peaks. The frequency of stable condition is higher in cold weather than in hot weather, and it is higher in calm weather than in windy weather in suburb, and the frequency of unstable condition is higher in rain weather than in heavy snow weather. The frequency of neutral and stable conditions are the highest before blowing sand but the unstable condition is the highest during and after sand blowing. The high frequency of atmospheric stability is in B, C and F category in spring and summer; the frequency of C and F category in summer in south suburbs and north suburbs is about 45%. The high frequency of atmospheric stability is B and E category in autumn (about 40%-50%). The high frequency of atmospheric stability is D category in urban, while is F category in south suburbs, north suburbs and north rural.
2016, 42(8):1007-1012.
DOI: 10.7519/j.issn.1000-0526.2016.08.011
Abstract:
Convective available potential energy (CAPE) is an important parameter in severe weather analysis and forecasting. The virtual temperature correction should be used in accurate CAPE calculation. MICAPS and GRADS both choose previous values of level of free convection (LFC) as the integral starting points in CAPE calculation when using virtual temperature corrections. LFC is defined as the altitude in the atmosphere where the temperature difference between air parcel and the environment turns from negative to positive. Using the same altitude of LFC in CAPE calculation with virtual temperature correction, is obviously contrary to the definition of LFC. Theoretical analysis in this paper indicates that LFC changes in CAPE calculation with virtual temperature correction, since two temperature profiles of air parcel and the environment change after correction, and their crossing point (LFC) also changes. The altitude of LFC is usually decreased using virtual temperature correction. Case study shows that although the CAPE increment is not so obvious when using the revised LFC in CAPE calculation with virtual temperature correction, it will be more reasonable in graphical representation and more precise for its physical meaning when considering the variation of LFC.
Convective available potential energy (CAPE) is an important parameter in severe weather analysis and forecasting. The virtual temperature correction should be used in accurate CAPE calculation. MICAPS and GRADS both choose previous values of level of free convection (LFC) as the integral starting points in CAPE calculation when using virtual temperature corrections. LFC is defined as the altitude in the atmosphere where the temperature difference between air parcel and the environment turns from negative to positive. Using the same altitude of LFC in CAPE calculation with virtual temperature correction, is obviously contrary to the definition of LFC. Theoretical analysis in this paper indicates that LFC changes in CAPE calculation with virtual temperature correction, since two temperature profiles of air parcel and the environment change after correction, and their crossing point (LFC) also changes. The altitude of LFC is usually decreased using virtual temperature correction. Case study shows that although the CAPE increment is not so obvious when using the revised LFC in CAPE calculation with virtual temperature correction, it will be more reasonable in graphical representation and more precise for its physical meaning when considering the variation of LFC.
2016, 42(8):1013-1019.
DOI: 10.7519/j.issn.1000-0526.2016.08.012
Abstract:
To use precipitation data more effectively， this paper analyzed the performance of DSC2 weighing gauge in precipitation observation. We selected the precipitation observation data from 13 national meteorological stations in Beijing from April to October 2013 to do research. The data were collected by weighing gauge, manual way and tipping gauge, respectively. The analysis was focused on the differences of total rainfall and daily precipitation observed by the three ways. The results showed that, among the samples, the errors of total precipitation from 12 stations are in line with the requirement of current operation and the grade judgment of daily precipitation by the three ways are basically consistent. Comparing the weighting gauge with manual way, the daily mean precipitation by weighing gauge shows a 0.13 mm less, and the daily precipitation correlation coefficient is 0.9968. The observation result by weighing gauge is averagely 0.17 mm less than the result by tipping gauge and the correlation coefficient is 0.9983.
To use precipitation data more effectively， this paper analyzed the performance of DSC2 weighing gauge in precipitation observation. We selected the precipitation observation data from 13 national meteorological stations in Beijing from April to October 2013 to do research. The data were collected by weighing gauge, manual way and tipping gauge, respectively. The analysis was focused on the differences of total rainfall and daily precipitation observed by the three ways. The results showed that, among the samples, the errors of total precipitation from 12 stations are in line with the requirement of current operation and the grade judgment of daily precipitation by the three ways are basically consistent. Comparing the weighting gauge with manual way, the daily mean precipitation by weighing gauge shows a 0.13 mm less, and the daily precipitation correlation coefficient is 0.9968. The observation result by weighing gauge is averagely 0.17 mm less than the result by tipping gauge and the correlation coefficient is 0.9983.
2016, 42(8):1020-1025.
DOI: 10.7519/j.issn.1000-0526.2016.08.013
Abstract:
The performance of mediumrange forecasts is verified and compared for the models of T639, ECMWF and Japan from March to May 2016. The results show that all of the three models can predict the variation and adjustment of the atmospheric circulation over Asian middle and high latitude areas well, of which ECMWF model performs the best. The three models all perform well in predicting the transitions of temperature at 850 hPa, as they all have smaller biases for Southern China than for Northern China, but ECMWF model shows a better comprehensive performance than the other two. Taking the sandstorm process seen in 3-5 March as a case, we see that T639 and ECMWF models are more effective than Japan model in mediumrange forecasting of the surface high pressure system which incurred the sandstorm weather process this time.
The performance of mediumrange forecasts is verified and compared for the models of T639, ECMWF and Japan from March to May 2016. The results show that all of the three models can predict the variation and adjustment of the atmospheric circulation over Asian middle and high latitude areas well, of which ECMWF model performs the best. The three models all perform well in predicting the transitions of temperature at 850 hPa, as they all have smaller biases for Southern China than for Northern China, but ECMWF model shows a better comprehensive performance than the other two. Taking the sandstorm process seen in 3-5 March as a case, we see that T639 and ECMWF models are more effective than Japan model in mediumrange forecasting of the surface high pressure system which incurred the sandstorm weather process this time.
2016, 42(8):1026-1032.
DOI: 10.7519/j.issn.1000-0526.2016.08.014
Abstract:
The main characteristics of the general atmospheric circulation in May 2016 were as follows： The circulation of polar vortex in the Northern Hemisphere was in a dipole pattern. The 500 hPa geopotential height presented the distribution of a fourwave pattern in the midhigh latitude of the Northern Hemisphere. The subtropical high of Northwest Pacific extended to more westward than usual with larger area, almost circling the globe. The monthly mean temperature was 16.3℃, being 0.1℃ higher than normal. The monthly mean precipitation amount was 82.8 mm, 19.1% more than the usual average (69.5 mm). The main weather characteristics in this month were that the onset of South China Sea summer monsoon happened in the last dekad of May; torrential rainfalls were seen frequently in the east of Southwestern China, the south of Southern China and South Yangtze River; and severe convective weather happened widely with greater intensities and severe thunderstorms and hail disaster.
The main characteristics of the general atmospheric circulation in May 2016 were as follows： The circulation of polar vortex in the Northern Hemisphere was in a dipole pattern. The 500 hPa geopotential height presented the distribution of a fourwave pattern in the midhigh latitude of the Northern Hemisphere. The subtropical high of Northwest Pacific extended to more westward than usual with larger area, almost circling the globe. The monthly mean temperature was 16.3℃, being 0.1℃ higher than normal. The monthly mean precipitation amount was 82.8 mm, 19.1% more than the usual average (69.5 mm). The main weather characteristics in this month were that the onset of South China Sea summer monsoon happened in the last dekad of May; torrential rainfalls were seen frequently in the east of Southwestern China, the south of Southern China and South Yangtze River; and severe convective weather happened widely with greater intensities and severe thunderstorms and hail disaster.
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ISSN:1000-0526 CN:11-2282/P