ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Volume 38,Issue 10,2012 Table of Contents
2012, 38(10):1161-1169.
DOI: 10.7519/j.issn.1000-0526.2012.10.001
Abstract:
The minute’s rainfall data and radar echoes in three heavy rain processes, which are chosen from Meiyu front, squall line and tropical system respectively in recent years, were used to analyze features of minute class rainfall distribution. The statistical features of three heavy rainfall processes were discussed through the precipitation rate, duration of precipitation and precipitation change’s rate. Finally, the average state of first one hour precipitation in strong precipitation periods was given. The results showed that minute’s precipitation series could be a very good performance of precipitation features in meso γ scale convective system. If combined with the radar echo and wavelet analysis, it could make up for the low time resolution of hour precipitation series. Analysis of samples in three heavy rain processes found that in the squall line, one single station only had once strong precipitation period, and the accumulative rainfall was less than 50 mm almost. It had high precipitation rate, but short duration periods and high variability, therefore, the prediction was difficult. However, under the influence of tropical convective systems, the single station precipitation was composed of many strong precipitation periods, and its accumulated rainfall up to 100 mm. Its precipitation rate was small, but had the longest duration time, and precipitation was more even. For the third heavy rain process, strong precipitation period in Meiyu front system corresponded to duration of 1-2 h, higher rate of precipitation than tropical convective systems, and the accumulative rainfall less than 100 mm. The precipitation nature was between squall line and tropical system, thus the prediction was the most complicated.
The minute’s rainfall data and radar echoes in three heavy rain processes, which are chosen from Meiyu front, squall line and tropical system respectively in recent years, were used to analyze features of minute class rainfall distribution. The statistical features of three heavy rainfall processes were discussed through the precipitation rate, duration of precipitation and precipitation change’s rate. Finally, the average state of first one hour precipitation in strong precipitation periods was given. The results showed that minute’s precipitation series could be a very good performance of precipitation features in meso γ scale convective system. If combined with the radar echo and wavelet analysis, it could make up for the low time resolution of hour precipitation series. Analysis of samples in three heavy rain processes found that in the squall line, one single station only had once strong precipitation period, and the accumulative rainfall was less than 50 mm almost. It had high precipitation rate, but short duration periods and high variability, therefore, the prediction was difficult. However, under the influence of tropical convective systems, the single station precipitation was composed of many strong precipitation periods, and its accumulated rainfall up to 100 mm. Its precipitation rate was small, but had the longest duration time, and precipitation was more even. For the third heavy rain process, strong precipitation period in Meiyu front system corresponded to duration of 1-2 h, higher rate of precipitation than tropical convective systems, and the accumulative rainfall less than 100 mm. The precipitation nature was between squall line and tropical system, thus the prediction was the most complicated.
2012, 38(10):1170-1181.
DOI: 10.7519/j.issn.1000-0526.2012.10.002
Abstract:
Data assimilation plays an important role in numerical weather prediction. Radar radial velocity data with high spatial and temporal resolution are one of the most useful data in data assimilation. In order to investigate the effects of radar radial velocity data and data assimilation interval on typhoon Matsa’s track and precipitation, the direct assimilation procedure of Doppler radar radial velocity data using the three dimensional variational (3DVAR)data assimilation method is set up for the Weather Research and Forecasting (WRF) model. Five numerical experiments are conducted for the simulation of typhoon Matsa (2005): a control run (CTL) without data assimilation, and four assimilated runs (ASSG, ASSGR, ASS6h, and ASS3h). Comparing the assimilation experiments (ASSG and ASSGR) and the control one (CTL) shows that, the radar radial velocity data can tune the typhoon structure and hence improve the simulation of typhoon Matsa’s track and precipitation. During the first 12 hours, the deviation between simulation and observation of the Matsa position decreases by 19.3 km and 25.9 km for ASSG run and ASSGR run, respectively. Although the simulated 12 hour accumulated precipitations are both overestimated by the ASSG and ASSGR runs in Ningbo, Zhoushan, and Jiaxing regions, it is much better than that by the CTL run. In order to investigate the effects of data assimilation interval on typhoon Matsa’s track and precipitation, three assimilated experiments with different data assimilation intervals are compared. Results show that small data assimilation interval can improve the result of the numerical experiment.
Data assimilation plays an important role in numerical weather prediction. Radar radial velocity data with high spatial and temporal resolution are one of the most useful data in data assimilation. In order to investigate the effects of radar radial velocity data and data assimilation interval on typhoon Matsa’s track and precipitation, the direct assimilation procedure of Doppler radar radial velocity data using the three dimensional variational (3DVAR)data assimilation method is set up for the Weather Research and Forecasting (WRF) model. Five numerical experiments are conducted for the simulation of typhoon Matsa (2005): a control run (CTL) without data assimilation, and four assimilated runs (ASSG, ASSGR, ASS6h, and ASS3h). Comparing the assimilation experiments (ASSG and ASSGR) and the control one (CTL) shows that, the radar radial velocity data can tune the typhoon structure and hence improve the simulation of typhoon Matsa’s track and precipitation. During the first 12 hours, the deviation between simulation and observation of the Matsa position decreases by 19.3 km and 25.9 km for ASSG run and ASSGR run, respectively. Although the simulated 12 hour accumulated precipitations are both overestimated by the ASSG and ASSGR runs in Ningbo, Zhoushan, and Jiaxing regions, it is much better than that by the CTL run. In order to investigate the effects of data assimilation interval on typhoon Matsa’s track and precipitation, three assimilated experiments with different data assimilation intervals are compared. Results show that small data assimilation interval can improve the result of the numerical experiment.
2012, 38(10):1182-1188.
DOI: 10.7519/j.issn.1000-0526.2012.10.003
Abstract:
Affected by strong earthquake and tsunami in east Japan, large amounts of radioactivity have been emitted from Fukushima Nuclear Power Plant since 12 March 2011. In this paper，Models 3/CMAQ is used to simulate the radioactive leak under ideal conditions. The results show that the radioactive releases mainly affect the vicinity of Fukushima and the northwest of the Pacific Ocean, the radioactive releases can disperse to higher altitudes, and the concentration of radioactive releases decreases exponentially with height increasing in source region. Moreover, radioactive releases have trivial effect on China through northeastern and eastern paths; and Models 3/CMAQ is capable of simulating radioactive leak accident.
Affected by strong earthquake and tsunami in east Japan, large amounts of radioactivity have been emitted from Fukushima Nuclear Power Plant since 12 March 2011. In this paper，Models 3/CMAQ is used to simulate the radioactive leak under ideal conditions. The results show that the radioactive releases mainly affect the vicinity of Fukushima and the northwest of the Pacific Ocean, the radioactive releases can disperse to higher altitudes, and the concentration of radioactive releases decreases exponentially with height increasing in source region. Moreover, radioactive releases have trivial effect on China through northeastern and eastern paths; and Models 3/CMAQ is capable of simulating radioactive leak accident.
2012, 38(10):1189-1195.
DOI: 10.7519/j.issn.1000-0526.2012.10.004
Abstract:
Based on the 87 stations selected along middle and lower reaches of the Changjiang River, and high density surface meteorological precipitation daily data during 1957-2007, the statistical methods are used to analyze the rainstorm process， and establish a rainstorm process impact assessment model. First select average rainfall, rainfall intensity, coverage and duration as four indicators, each indicator uses the normal transformation or gamma distribution to fit, then uses the appropriate distribution’s inverse function of probability density function to determine the theoretical values of return period as the grade level standards， which can be divided into five levels. Finally, a composite assessment model of rainstorm process is set up. In this paper the model is applied to assessment of five rainstorm processes from the end of June to August in 1999, and the results show that the effect is good, and can be put into operation.
Based on the 87 stations selected along middle and lower reaches of the Changjiang River, and high density surface meteorological precipitation daily data during 1957-2007, the statistical methods are used to analyze the rainstorm process， and establish a rainstorm process impact assessment model. First select average rainfall, rainfall intensity, coverage and duration as four indicators, each indicator uses the normal transformation or gamma distribution to fit, then uses the appropriate distribution’s inverse function of probability density function to determine the theoretical values of return period as the grade level standards， which can be divided into five levels. Finally, a composite assessment model of rainstorm process is set up. In this paper the model is applied to assessment of five rainstorm processes from the end of June to August in 1999, and the results show that the effect is good, and can be put into operation.
2012, 38(10):1196-1206.
DOI: 10.7519/j.issn.1000-0526.2012.10.005
Abstract:
With hourly intensive surface observations, satellite remote sensed temperature of black body (TBB) and 3 hourly radio soundings, an analysis is carried out to investigate the diurnal changes of convective rainfall and atmospheric physical variables along the middle valleys of Yangtze River. The results are as follows： the convective rainfall is of obvious diurnal changes, with a rainfall maximum (minimum) at 1500 BT (0100 BT). The surface and sounding physical variables are also of clear diurnal changes. The diurnal variation of surface temperature is the most obvious, with a mean diurnal range of 9℃, while the diurnal range of dew point temperature is only about 1℃. The diurnal change of relative humidity is mainly caused by the temperature diurnal variation. The spatial distribution of surface temperature diurnal changes is influenced by the topography. The temperature rising (dropping) in the mountainous areas is larger than in the plain areas in the daytime (nighttime). The diurnal change of temperature gradient due to the topographic difference can drive topographically near surface thermal flow. The convergence (divergence) flows occur in the mountainous areas (plain areas) in the daytime, vice versa in the nighttime. The stability decrease in the lower atmosphere and the CAPE increase are beneficial to the afternoon thermal convection initiation in the daytime. The lowering of lifting condensation level (LCL), the increase of relative humidity and the increase of air column precipitable water vapor (PW) are favorable for the development of long life early morning convective systems in the nighttime.
With hourly intensive surface observations, satellite remote sensed temperature of black body (TBB) and 3 hourly radio soundings, an analysis is carried out to investigate the diurnal changes of convective rainfall and atmospheric physical variables along the middle valleys of Yangtze River. The results are as follows： the convective rainfall is of obvious diurnal changes, with a rainfall maximum (minimum) at 1500 BT (0100 BT). The surface and sounding physical variables are also of clear diurnal changes. The diurnal variation of surface temperature is the most obvious, with a mean diurnal range of 9℃, while the diurnal range of dew point temperature is only about 1℃. The diurnal change of relative humidity is mainly caused by the temperature diurnal variation. The spatial distribution of surface temperature diurnal changes is influenced by the topography. The temperature rising (dropping) in the mountainous areas is larger than in the plain areas in the daytime (nighttime). The diurnal change of temperature gradient due to the topographic difference can drive topographically near surface thermal flow. The convergence (divergence) flows occur in the mountainous areas (plain areas) in the daytime, vice versa in the nighttime. The stability decrease in the lower atmosphere and the CAPE increase are beneficial to the afternoon thermal convection initiation in the daytime. The lowering of lifting condensation level (LCL), the increase of relative humidity and the increase of air column precipitable water vapor (PW) are favorable for the development of long life early morning convective systems in the nighttime.
2012, 38(10):1207-1216.
DOI: 10.7519/j.issn.1000-0526.2012.10.006
Abstract:
Based on the meteorological data collected from 1084 stations over North China, Central China and East China from 1971 to 2000, features of interdecadal variation of thunderstorm, hail and gale wind in the south of the Yangtze River (31°N southward), Jiang Huai area and Huang Huai (31°N to 37°N) and the north of the Yellow River (37°N northward) have been analyzed. The analysis results have indicated that the frequency of thunderstorm, hail and gale wind has a decreasing trend. The inter decadal variation of thunderstorm in the south of the Yangtze River shows a more significant decreasing trend, hail decreases most obviously in the north of the Yellow River, and gale wind decreases evidently in all these three regions. The hail often occurs with gale wind, and more frequent in the plateau and the mountain region than in the plain. It takes place most in northern North China and Central Inner Mongolia. The analysis of relevant conditions for the generation and development of the mesoscale convective system such as water vapor, thermodynamic instability and dynamical lifting has shown that the reduction of convection weather has a close relation to the decline of moisture and dynamic conditions. The composite index SWEAT (severe weather threat) including thermodynamic, dynamic and moisture conditions expresses the similar characteristics to the convection weather in the spatial distribution or the evolution trend in 30 years.
Based on the meteorological data collected from 1084 stations over North China, Central China and East China from 1971 to 2000, features of interdecadal variation of thunderstorm, hail and gale wind in the south of the Yangtze River (31°N southward), Jiang Huai area and Huang Huai (31°N to 37°N) and the north of the Yellow River (37°N northward) have been analyzed. The analysis results have indicated that the frequency of thunderstorm, hail and gale wind has a decreasing trend. The inter decadal variation of thunderstorm in the south of the Yangtze River shows a more significant decreasing trend, hail decreases most obviously in the north of the Yellow River, and gale wind decreases evidently in all these three regions. The hail often occurs with gale wind, and more frequent in the plateau and the mountain region than in the plain. It takes place most in northern North China and Central Inner Mongolia. The analysis of relevant conditions for the generation and development of the mesoscale convective system such as water vapor, thermodynamic instability and dynamical lifting has shown that the reduction of convection weather has a close relation to the decline of moisture and dynamic conditions. The composite index SWEAT (severe weather threat) including thermodynamic, dynamic and moisture conditions expresses the similar characteristics to the convection weather in the spatial distribution or the evolution trend in 30 years.
2012, 38(10):1217-1224.
DOI: 10.7519/j.issn.1000-0526.2012.10.007
Abstract:
By using hail data at 148 stations in Sichuan Province during 1978—2007, the spatial and temporal characteristics of hail days were analyzed. The results show that hail days are more in plateau and mountain areas than basin areas. The number of hail days has declined as a whole, especially in plateau areas. The hail appeared with the highest frequency in summer, less in spring and autumn, and the least in winter. In the interannual variations, the periods of quasi biennial oscillation and 6 year oscillation are primary. The similar inter monthly variation in hail days happened to the surrounding stations which have the similar altitudes.
By using hail data at 148 stations in Sichuan Province during 1978—2007, the spatial and temporal characteristics of hail days were analyzed. The results show that hail days are more in plateau and mountain areas than basin areas. The number of hail days has declined as a whole, especially in plateau areas. The hail appeared with the highest frequency in summer, less in spring and autumn, and the least in winter. In the interannual variations, the periods of quasi biennial oscillation and 6 year oscillation are primary. The similar inter monthly variation in hail days happened to the surrounding stations which have the similar altitudes.
2012, 38(10):1225-1231.
DOI: 10.7519/j.issn.1000-0526.2012.10.008
Abstract:
According to routine surface meteorological data, upper air sounding data and environmental pollutant observation data from 1998 to 2010 in Hangzhou, we did a comprehensive analysis of the haze characteristics and formation mechanism under the main synoptic situations, the typically meteorological elements as well as environmental pollution. The results indicate that the high pressure weather situation has a significant effect on haze in Hangzhou, while cyclone and easterly weather situation are less likely to occurring of haze. Neutral stratification plays a leading role in atmospheric stability under haze weather, the frequency is up to 54.3%. The frequency of haze under inversion conditions at 08:00 BT is higher than that at 20:00 BT, the average inversion strength under haze is higher than no haze weather, the inversion thickness, the maximum inversion strength and maximum thickness on average are lower than those of no haze weather. The concentrations of pollutants of PM10, SO2 and NO2 were decreased by 33.3%, 20.0% and 18.2% respectively on no haze days compared to haze days. With the increase in haze levels, the concentration of different pollutants also increases. Particles is one of the main reasons for reducing visibility. In addition, Hangzhou special terrain environment plays a role in leading to the occurrence of haze. Above results are significant to understand the occurrence of haze weather and develop the alarming and forecasting work.
According to routine surface meteorological data, upper air sounding data and environmental pollutant observation data from 1998 to 2010 in Hangzhou, we did a comprehensive analysis of the haze characteristics and formation mechanism under the main synoptic situations, the typically meteorological elements as well as environmental pollution. The results indicate that the high pressure weather situation has a significant effect on haze in Hangzhou, while cyclone and easterly weather situation are less likely to occurring of haze. Neutral stratification plays a leading role in atmospheric stability under haze weather, the frequency is up to 54.3%. The frequency of haze under inversion conditions at 08:00 BT is higher than that at 20:00 BT, the average inversion strength under haze is higher than no haze weather, the inversion thickness, the maximum inversion strength and maximum thickness on average are lower than those of no haze weather. The concentrations of pollutants of PM10, SO2 and NO2 were decreased by 33.3%, 20.0% and 18.2% respectively on no haze days compared to haze days. With the increase in haze levels, the concentration of different pollutants also increases. Particles is one of the main reasons for reducing visibility. In addition, Hangzhou special terrain environment plays a role in leading to the occurrence of haze. Above results are significant to understand the occurrence of haze weather and develop the alarming and forecasting work.
2012, 38(10):1232-1237.
DOI: 10.7519/j.issn.1000-0526.2012.10.009
Abstract:
This paper briefly reviews recent advances in the observation and modeling of urban weather and climate. Then future prospects for several research avenues are speculated, which include the numerical simulation of urban meteorology, new observation technology and assimilation application, the interaction between observation and numerical simulation, the impact of urbanization on weather and climate, the usage of urban climate resources and the mitigation of urban heat island, and the impact of urbanization on the atmospheric environment and human health. Furthermore, the key scientific questions are raised, e.g. the urban canopy model development, urban hydrological processes and urban precipitation, urban boundary layer and other model physics, and model evaluation, etc.
This paper briefly reviews recent advances in the observation and modeling of urban weather and climate. Then future prospects for several research avenues are speculated, which include the numerical simulation of urban meteorology, new observation technology and assimilation application, the interaction between observation and numerical simulation, the impact of urbanization on weather and climate, the usage of urban climate resources and the mitigation of urban heat island, and the impact of urbanization on the atmospheric environment and human health. Furthermore, the key scientific questions are raised, e.g. the urban canopy model development, urban hydrological processes and urban precipitation, urban boundary layer and other model physics, and model evaluation, etc.
2012, 38(10):1238-1246.
DOI: 10.7519/j.issn.1000-0526.2012.10.010
Abstract:
Operational positioning and forecast errors of tropical cyclones (TC) over the western North Pacific in 2011 are evaluated. The evaluations are performed on the TC’s positioning, the deterministic track and intensity forecasts, and the track ensemble prediction. The results show that the TC average operational positioning error is 24.9 km. The average errors of domestic integrated track forecast in 24 h, 48 h and 72 h are 112.6 km, 209.7 km and 333.6 km, respectively, which are 121.4 km, 220.1 km and 380.5 km for numerical weather prediction (NWP) models, and better than those of 2010. However, the results also show that the NWP intensity forecasting capability is still weaker than objective methods. ECMWF ensemble prediction system (EPS) shows the best performance among the 7 EPS methods, followed by NCEP EPS, occasionally, these two systems have near and even beyond subjective track forecast level. CMA GEFS EPS was located at the middle level.
Operational positioning and forecast errors of tropical cyclones (TC) over the western North Pacific in 2011 are evaluated. The evaluations are performed on the TC’s positioning, the deterministic track and intensity forecasts, and the track ensemble prediction. The results show that the TC average operational positioning error is 24.9 km. The average errors of domestic integrated track forecast in 24 h, 48 h and 72 h are 112.6 km, 209.7 km and 333.6 km, respectively, which are 121.4 km, 220.1 km and 380.5 km for numerical weather prediction (NWP) models, and better than those of 2010. However, the results also show that the NWP intensity forecasting capability is still weaker than objective methods. ECMWF ensemble prediction system (EPS) shows the best performance among the 7 EPS methods, followed by NCEP EPS, occasionally, these two systems have near and even beyond subjective track forecast level. CMA GEFS EPS was located at the middle level.
2012, 38(10):1247-1254.
DOI: 10.7519/j.issn.1000-0526.2012.10.011
Abstract:
The pre-flood season (also named as early rainy season) in South China in 2012 begins in the 2nd pentad in April, and ends in the 5th pentad in June. The pre-flood season has experienced three different periods. The first one is the frontal precipitation period from 2nd pentad in April to 3rd pentad in May, with precipitation over 25% more than normal in most Jiangnan area and most South China. The second period is the dry period from 4th pentad in May to 2nd pentad in June, with precipitation over 50% less than normal in central and eastern South China. The last one is the summer monsoon precipitation period during 3rd-5th pentads in June, with precipitation over 50% more than normal in southeastern Jiangnan area and central-western South China. Analysis of the atmospheric circulation anomalies during each period of the pre-flood season in South China in 2012 indicates that after the pre-flood season onset, more frontal precipitation during the first period is caused by the increased high ridge over the Ural Mountains and the anomalous convergent moisture flux in South China due to the intensified low-level western Pacific subtropical high (WPSH); during the dry period, the South China Sea summer monsoon (SCSSM) is weaker and the WPSH abnormally shifts northward for three pentads. In the last summer monsoon precipitation period, the anomalously intensified SCSSM, the southward WPSH, as well as the enhanced monsoon trough over the Bay of Bengal favor anomalously more precipitation in South China.
The pre-flood season (also named as early rainy season) in South China in 2012 begins in the 2nd pentad in April, and ends in the 5th pentad in June. The pre-flood season has experienced three different periods. The first one is the frontal precipitation period from 2nd pentad in April to 3rd pentad in May, with precipitation over 25% more than normal in most Jiangnan area and most South China. The second period is the dry period from 4th pentad in May to 2nd pentad in June, with precipitation over 50% less than normal in central and eastern South China. The last one is the summer monsoon precipitation period during 3rd-5th pentads in June, with precipitation over 50% more than normal in southeastern Jiangnan area and central-western South China. Analysis of the atmospheric circulation anomalies during each period of the pre-flood season in South China in 2012 indicates that after the pre-flood season onset, more frontal precipitation during the first period is caused by the increased high ridge over the Ural Mountains and the anomalous convergent moisture flux in South China due to the intensified low-level western Pacific subtropical high (WPSH); during the dry period, the South China Sea summer monsoon (SCSSM) is weaker and the WPSH abnormally shifts northward for three pentads. In the last summer monsoon precipitation period, the anomalously intensified SCSSM, the southward WPSH, as well as the enhanced monsoon trough over the Bay of Bengal favor anomalously more precipitation in South China.
2012, 38(10):1255-1266.
DOI: 10.7519/j.issn.1000-0526.2012.10.012
Abstract:
Precipitation characteristics, environment conditions, generation and development of the mesoscale convective system that brought about the extreme torrential rain in Beijing on 21 July 2012 were analyzed comprehensively in this paper by using various conventional and unconventional data. The results showed that the extreme torrential rain had the characteristics of long duration, great rainfall and wide coverage area and its process consisted of warm area precipitation and frontal precipitation. The warm area rainfall started earlier, the severe precipitation center was scattered and lasted long while the frontal rainfallprocess contained several severe rainfall centers with high precipitation efficiency, lasting a short time.Environment conditions of the mesoscale convective system that triggered this extreme severe rainfall were analyzed. The results showed that interactions of high level divergence, the wind shear and convergence with the vortex in the lower troposphere and the surface wind convergence line provided favorable environment to the severe extreme rain. The warm humid airs from the tropical and sub tropical zones converged over the torrential rain region, continuous and sufficient water vapor manifested as high atmospheric column of precipitable water and strong low level water vapor convergence and other extreme vapor conditions for the torrential rain. In addition, the intense precipitation was triggered by the vortex wind shear, wind disturbance on low level jet, surface wind convergence line and the effect of terrain under the condition of the plentiful water vapour and maintained. With the cold front moved eastward, heavy frontal rainfall was brought by the development and evolution of convective system made by the cold air and the suitable vertical wind shear.Generation and development processes of the mesoscale convective system were also studied. The findings suggested that stratiform cloud precipitation and dispersed convective precipitation occurred firstly in the precipitation process. The warm and steady stratiform cloud precipitation changed to be highly organized convectional precipitation as the cold dry air invaded. Many small scale and mesoscale convective clusters developed into mesoscale convective complex (MCC), leading to the extreme severe precipitation. Since all the directions of the echo long axis, terrain and echo movement were parallel, train effect was obviously seen in the radar echo imegery during this precipitation process. Meanwhile, the radar echo had the characteristics of backward propagation and low centroid which was similar to tropical heavy rainfalls. Finally, a series of scientific problems were proposed according to the integrated analysis on the observation data of this rare torrential rain event, such as the causes for the extreme torrential rain and the extreme rich water vapor, mechanisms for the warm area torrential rain in the north of China, the mechanism for the train effect and backward propagation, mechanisms for the organization and maintenance of the convective cells, the simulation and analysis ability of the numerical models to extreme torrential rains and so on.
Precipitation characteristics, environment conditions, generation and development of the mesoscale convective system that brought about the extreme torrential rain in Beijing on 21 July 2012 were analyzed comprehensively in this paper by using various conventional and unconventional data. The results showed that the extreme torrential rain had the characteristics of long duration, great rainfall and wide coverage area and its process consisted of warm area precipitation and frontal precipitation. The warm area rainfall started earlier, the severe precipitation center was scattered and lasted long while the frontal rainfallprocess contained several severe rainfall centers with high precipitation efficiency, lasting a short time.Environment conditions of the mesoscale convective system that triggered this extreme severe rainfall were analyzed. The results showed that interactions of high level divergence, the wind shear and convergence with the vortex in the lower troposphere and the surface wind convergence line provided favorable environment to the severe extreme rain. The warm humid airs from the tropical and sub tropical zones converged over the torrential rain region, continuous and sufficient water vapor manifested as high atmospheric column of precipitable water and strong low level water vapor convergence and other extreme vapor conditions for the torrential rain. In addition, the intense precipitation was triggered by the vortex wind shear, wind disturbance on low level jet, surface wind convergence line and the effect of terrain under the condition of the plentiful water vapour and maintained. With the cold front moved eastward, heavy frontal rainfall was brought by the development and evolution of convective system made by the cold air and the suitable vertical wind shear.Generation and development processes of the mesoscale convective system were also studied. The findings suggested that stratiform cloud precipitation and dispersed convective precipitation occurred firstly in the precipitation process. The warm and steady stratiform cloud precipitation changed to be highly organized convectional precipitation as the cold dry air invaded. Many small scale and mesoscale convective clusters developed into mesoscale convective complex (MCC), leading to the extreme severe precipitation. Since all the directions of the echo long axis, terrain and echo movement were parallel, train effect was obviously seen in the radar echo imegery during this precipitation process. Meanwhile, the radar echo had the characteristics of backward propagation and low centroid which was similar to tropical heavy rainfalls. Finally, a series of scientific problems were proposed according to the integrated analysis on the observation data of this rare torrential rain event, such as the causes for the extreme torrential rain and the extreme rich water vapor, mechanisms for the warm area torrential rain in the north of China, the mechanism for the train effect and backward propagation, mechanisms for the organization and maintenance of the convective cells, the simulation and analysis ability of the numerical models to extreme torrential rains and so on.
2012, 38(10):1267-1277.
DOI: 10.7519/j.issn.1000-0526.2012.10.013
Abstract:
This paper is the second part of “Analysis and thinking on the extremes of the 21 July 2012 torrential rain in Beijing”. The first part of “Observation Analysis and Thinking” has analyzed the precipitation features, water vapor conditions, environmental conditions, generation and development of the mesoscale convective systems (MCSs) during the process of the severe torrential rain. As the second part of the series studies, this paper mainly focused on the impact factors of the extreme rainfall, i.e., precipitation efficiency, water vapor, ascending motion and duration and so on, to explore the causes of the extreme torrential rain by using various observation and model data that are often used in operations. The results showed that this extreme severe rainfall event happened under a typical circulation pattern of North China torrential rains. The interaction of high level wind divergence with the low level vortex and wind shear directly triggered the extreme rain event. The comparatively high relative humidity and thick humid layer, low lifting condensation height and free convection height as well as the characteristcs of tropical torrential rains improved the precipitation efficiency of this severely heavy rain process. The extreme high water vapor content (with the atmospheric precipitable water vapor getting to 60-80 mm) and the abnormity of associated physical quantity can be judged as the extreme severe precipitation event. The middle and low level troposphere was instable conditionally, while the upper level had the characteristics of humid neutral stratification. With a medium CAPE value and convective instability enhanced by upper level dry intrusion, the upward motion was intensified. MCS was generated and developed in the warm areas due to the combined actions of vortex wind shear and the terrain in the North China region. The northward jump of vortex and the backward propagation of MCS made the warm area MCS more slowly eastward forming the “train effect” and resulting in the long lasting precipitation. Finally, this paper discussed the methods of forecasting extremely severe rainfalls.
This paper is the second part of “Analysis and thinking on the extremes of the 21 July 2012 torrential rain in Beijing”. The first part of “Observation Analysis and Thinking” has analyzed the precipitation features, water vapor conditions, environmental conditions, generation and development of the mesoscale convective systems (MCSs) during the process of the severe torrential rain. As the second part of the series studies, this paper mainly focused on the impact factors of the extreme rainfall, i.e., precipitation efficiency, water vapor, ascending motion and duration and so on, to explore the causes of the extreme torrential rain by using various observation and model data that are often used in operations. The results showed that this extreme severe rainfall event happened under a typical circulation pattern of North China torrential rains. The interaction of high level wind divergence with the low level vortex and wind shear directly triggered the extreme rain event. The comparatively high relative humidity and thick humid layer, low lifting condensation height and free convection height as well as the characteristcs of tropical torrential rains improved the precipitation efficiency of this severely heavy rain process. The extreme high water vapor content (with the atmospheric precipitable water vapor getting to 60-80 mm) and the abnormity of associated physical quantity can be judged as the extreme severe precipitation event. The middle and low level troposphere was instable conditionally, while the upper level had the characteristics of humid neutral stratification. With a medium CAPE value and convective instability enhanced by upper level dry intrusion, the upward motion was intensified. MCS was generated and developed in the warm areas due to the combined actions of vortex wind shear and the terrain in the North China region. The northward jump of vortex and the backward propagation of MCS made the warm area MCS more slowly eastward forming the “train effect” and resulting in the long lasting precipitation. Finally, this paper discussed the methods of forecasting extremely severe rainfalls.
FANG Chong
,
MAO Dongyan
,
ZHANG Xiaowen
,
LIN Yinjing
,
ZHU Wenjian
,
ZHANG Tao
,
CHEN Yun
,
SHENG Jie
,
LAN Yu
,
LIN Yi
,
ZHENG Yongguang
2012, 38(10):1278-1287.
DOI: 10.7519/j.issn.1000-0526.2012.10.014
Abstract:
Using the data of conventional and automatic weather stations (AWS), Doppler radar, satellite and wind profiler radar （WPR） as well as the associated NCEP reanalysis data (1°×1°), this paper analyzed the convection conditions and mesoscale characteristics of an extreme rainstorm in Beijing and its surrounding areas on 21 July 2012. The results suggested that sufficient moisture， convective instability, continuous “train effect” of the convection systems and a low mass center precipitation echo structure with high precipitation efficiency were the main causes for the generation and development of the extreme heavy rainfalls. It also showed that the newborn and severely developing convective cells were located at the intersection part of low level shear line and surface convergence line. The movement direction of convective cells and the presence of “train effect” can approximately be judged according to the direction and speed of the mid level winds as well as the position and direction of surface convergence line. Mesoscale analysis on the severe precipitation was made based on satellite infrared cloud images and radar reflectivity data, and the results showed that there were three stages in the process of the rainstorm: (1) The first stage is the generation period of the convective systems before their strongly developing; (2) The second stage is the most severely developing period in which extreme rainstorm can be observed by most meteorological stations in Beijing; (3) The third stage is significantly diminishing period of the severe convection and precipitation.
Using the data of conventional and automatic weather stations (AWS), Doppler radar, satellite and wind profiler radar （WPR） as well as the associated NCEP reanalysis data (1°×1°), this paper analyzed the convection conditions and mesoscale characteristics of an extreme rainstorm in Beijing and its surrounding areas on 21 July 2012. The results suggested that sufficient moisture， convective instability, continuous “train effect” of the convection systems and a low mass center precipitation echo structure with high precipitation efficiency were the main causes for the generation and development of the extreme heavy rainfalls. It also showed that the newborn and severely developing convective cells were located at the intersection part of low level shear line and surface convergence line. The movement direction of convective cells and the presence of “train effect” can approximately be judged according to the direction and speed of the mid level winds as well as the position and direction of surface convergence line. Mesoscale analysis on the severe precipitation was made based on satellite infrared cloud images and radar reflectivity data, and the results showed that there were three stages in the process of the rainstorm: (1) The first stage is the generation period of the convective systems before their strongly developing; (2) The second stage is the most severely developing period in which extreme rainstorm can be observed by most meteorological stations in Beijing; (3) The third stage is significantly diminishing period of the severe convection and precipitation.
2012, 38(10):1288-1294.
DOI: 10.7519/j.issn.1000-0526.2012.10.015
Abstract:
Using the advanced technology of mobile communications and smart phone, the modern meteorological operation and weather modification, we developed an operation system which has realized the collecting real time information of weather modification, visual display, and information transmission for providing a new way to operational personnel to timely get the information. The system is stable and practical, so it is increasing the technological content of precipitation enhancement and strengthening the professional skills of the provincial center of weather modification. This paper describes the system’s design, framework, function and application, etc.
Using the advanced technology of mobile communications and smart phone, the modern meteorological operation and weather modification, we developed an operation system which has realized the collecting real time information of weather modification, visual display, and information transmission for providing a new way to operational personnel to timely get the information. The system is stable and practical, so it is increasing the technological content of precipitation enhancement and strengthening the professional skills of the provincial center of weather modification. This paper describes the system’s design, framework, function and application, etc.
2012, 38(10):1295-1300.
DOI: 10.7519/j.issn.1000-0526.2012.10.016
Abstract:
Aiming at some current problems of quality control in real time temperature measurements, a dynamic method based on k means clustering algorithm is proposed. The algorithm first divides the temperature sample points in the region into a number of clusters according to their similar temperatures by k means, and then for each sample point in the clusters the algorithm checks its outlier ratio and outlier speed in order to determine the final quality of the point. Compared with conventional temperature quality control methods, the algorithm uses an idea of the comparison of the single point temperature with the overall temperature, and it does not need to pre set the reference temperature value, thus it is a more real time and scientific temperature quality control method. Also, the complexity of the algorithm is low, and it is proper for the calculation of large temperature input data sets.
Aiming at some current problems of quality control in real time temperature measurements, a dynamic method based on k means clustering algorithm is proposed. The algorithm first divides the temperature sample points in the region into a number of clusters according to their similar temperatures by k means, and then for each sample point in the clusters the algorithm checks its outlier ratio and outlier speed in order to determine the final quality of the point. Compared with conventional temperature quality control methods, the algorithm uses an idea of the comparison of the single point temperature with the overall temperature, and it does not need to pre set the reference temperature value, thus it is a more real time and scientific temperature quality control method. Also, the complexity of the algorithm is low, and it is proper for the calculation of large temperature input data sets.
2012, 38(10):1301-1306.
DOI: 10.7519/j.issn.1000-0526.2012.10.017
Abstract:
Five agronomic activities such as the fruit bagging index and a seasonal growth suitability prediction model for main forest fruits such as apple were respectively established by using the fuzzy comprehensive evaluation method and the expertise assessment. On this basis, we developed agro-weather forecast system for the forest fruits of Shaanxi Province based on a B/S (Browser/Server), and the automatic calculation and output were therefore achieved for predicting the agricultural activities and the growth suitability weather each 24-h before 3 days.
Five agronomic activities such as the fruit bagging index and a seasonal growth suitability prediction model for main forest fruits such as apple were respectively established by using the fuzzy comprehensive evaluation method and the expertise assessment. On this basis, we developed agro-weather forecast system for the forest fruits of Shaanxi Province based on a B/S (Browser/Server), and the automatic calculation and output were therefore achieved for predicting the agricultural activities and the growth suitability weather each 24-h before 3 days.
2012, 38(10):1307-1312.
DOI: 10.7519/j.issn.1000-0526.2012.10.018
Abstract:
The main characteristics of the general atmospheric circulation in July 2012 are as follows: The circulation presented a pattern of two highs and one deep trough at the middle high latitudes over Eurasia, and the upper troughs were active. The northwestern pacific subtropical high was weaker than normal. The monthly mean precipitation amount was 135 mm, which is 14.4% more than normal. The monthly mean temperature was 22.1℃, being 0.4℃ higher than normal. There were 8 heavy rainfall processes, and extreme precipitation records were observed at many stations. Four tropical cyclones were generated over the northwestern Pacific, however, only one landed on China. The number of high temperature days is obviously more than normal in some areas, such as Jiangnan, Jianghuai, Jianghan, and huanghuai etc.
The main characteristics of the general atmospheric circulation in July 2012 are as follows: The circulation presented a pattern of two highs and one deep trough at the middle high latitudes over Eurasia, and the upper troughs were active. The northwestern pacific subtropical high was weaker than normal. The monthly mean precipitation amount was 135 mm, which is 14.4% more than normal. The monthly mean temperature was 22.1℃, being 0.4℃ higher than normal. There were 8 heavy rainfall processes, and extreme precipitation records were observed at many stations. Four tropical cyclones were generated over the northwestern Pacific, however, only one landed on China. The number of high temperature days is obviously more than normal in some areas, such as Jiangnan, Jianghuai, Jianghan, and huanghuai etc.
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ISSN:1000-0526 CN:11-2282/P