ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Volume 42,Issue 2,2016 Table of Contents
2016, 42(2):129-143.
DOI: 10.7519/j.issn.1000-0526.2016.02.001
Abstract:
Severe convective weather is hard to forecast because of the character of small scale and rapid development. Fuzzy verification methods can get evaluation information at different spatial scales by using a spatial window or neighborhood surrounding the forecast and/or observed points, and are introduced into the verification of severe convective weather in this article. Focusing on the three types of severe convective weather, some operational nowcasting products like as onehour reflectivity extrapolation product of the Chinese Meteorological Administration (CMA) SWAN (Severe Weather Analysis and Nowcasting) system, are verified using the fuzzy method. Then, three ideal severe convective weather models are also built and verified to give a further study on the abovementioned methods. The results show that compared to traditional metrics with the stagey of “point to point”, fuzzy verification can glean additional information in different scales and evaluation strategies, evaluating forecasts more comprehensively and objectively. Based on different evaluation strategies, one forecast has different optimal scales and each fuzzy verification method has its own feature and application. When forecast has large bias, fuzzy verification methods can still give effective or “useful” scores while traditional metric can only give poor scores. For the severe convective events with characteristics of high thresholds and small scales, the fuzzy verification methods including minimum coverage with low fraction, fuzzy logic and multievent contingency table show more potential value than the traditional ones.
Severe convective weather is hard to forecast because of the character of small scale and rapid development. Fuzzy verification methods can get evaluation information at different spatial scales by using a spatial window or neighborhood surrounding the forecast and/or observed points, and are introduced into the verification of severe convective weather in this article. Focusing on the three types of severe convective weather, some operational nowcasting products like as onehour reflectivity extrapolation product of the Chinese Meteorological Administration (CMA) SWAN (Severe Weather Analysis and Nowcasting) system, are verified using the fuzzy method. Then, three ideal severe convective weather models are also built and verified to give a further study on the abovementioned methods. The results show that compared to traditional metrics with the stagey of “point to point”, fuzzy verification can glean additional information in different scales and evaluation strategies, evaluating forecasts more comprehensively and objectively. Based on different evaluation strategies, one forecast has different optimal scales and each fuzzy verification method has its own feature and application. When forecast has large bias, fuzzy verification methods can still give effective or “useful” scores while traditional metric can only give poor scores. For the severe convective events with characteristics of high thresholds and small scales, the fuzzy verification methods including minimum coverage with low fraction, fuzzy logic and multievent contingency table show more potential value than the traditional ones.
2016, 42(2):144-155.
DOI: 10.7519/j.issn.1000-0526.2016.02.002
Abstract:
In order to understand the environmental characteristics of shorttime severe rainfall event (hourly rainfall amount ≥50 mm) in Pearl River Delta, we researched the weather flow, Tlnp chart patterns and key physical parameters of 68 shorttime intense rain event for nearly 7 years (2007-2013) by using automatic weather station data, sounding data, satellite data in the Pearl River Delta region. The results showed that such severe rainfalls in Pearl River Delta are characterized by, first, the weather flow patterns, which include typhoon type, southwest monsoon type, Beibu Gulf low pressure type, cold shear line type and tropical cloud type. Different types have different frequencies in different seasons. Secondly, temperature profiles and wet adiabat are very close in Tlnp in most of the shorttime severe rain events, and the water vapor content are rich in the whole layer. Thirdly, the features of the key parameters of the severe rainfalls are that mainly the value of T850-T500 is small, usually 21-23℃ with a weak unstable stratification, higher ground dew point and PW. CAPE values are more moderate, mostly less than 1500 J·kg-1. CIN and vertical wind shear of 0-6 km are relatively weak, and lowlevel jets appear in most cases. The key conditions for most of the shorttime severe rainfall process are not the highaltitude cold air intrusion, but the warm air transport from low level. Although small CAPE value limits updraft, the cloud base of specific humidity is high. If combining the configuration method of flow pattern (type), the key environmental parameters, the range of parameters to set appropriate threshold according to the box whisker plots, we can provide valuable reference to rebuild the forecast method of shorttime severe rainfall in the Pearl River Delta region.
In order to understand the environmental characteristics of shorttime severe rainfall event (hourly rainfall amount ≥50 mm) in Pearl River Delta, we researched the weather flow, Tlnp chart patterns and key physical parameters of 68 shorttime intense rain event for nearly 7 years (2007-2013) by using automatic weather station data, sounding data, satellite data in the Pearl River Delta region. The results showed that such severe rainfalls in Pearl River Delta are characterized by, first, the weather flow patterns, which include typhoon type, southwest monsoon type, Beibu Gulf low pressure type, cold shear line type and tropical cloud type. Different types have different frequencies in different seasons. Secondly, temperature profiles and wet adiabat are very close in Tlnp in most of the shorttime severe rain events, and the water vapor content are rich in the whole layer. Thirdly, the features of the key parameters of the severe rainfalls are that mainly the value of T850-T500 is small, usually 21-23℃ with a weak unstable stratification, higher ground dew point and PW. CAPE values are more moderate, mostly less than 1500 J·kg-1. CIN and vertical wind shear of 0-6 km are relatively weak, and lowlevel jets appear in most cases. The key conditions for most of the shorttime severe rainfall process are not the highaltitude cold air intrusion, but the warm air transport from low level. Although small CAPE value limits updraft, the cloud base of specific humidity is high. If combining the configuration method of flow pattern (type), the key environmental parameters, the range of parameters to set appropriate threshold according to the box whisker plots, we can provide valuable reference to rebuild the forecast method of shorttime severe rainfall in the Pearl River Delta region.
2016, 42(2):156-165.
DOI: 10.7519/j.issn.1000-0526.2016.02.003
Abstract:
By using the surface observational data, typhoon track data and ECMWF global reanalysis data, as well as the objective synoptic analysis technique (OSAT), tropical cyclone (TC) track similarity area index (TSAI) and the airflow trajectory model (HYSPLIT4.9), this paper analyzes the characteristics and the causes of the extreme precipitation created by the Severe Typhoon Fitow over the coastal region of Southeast China, and reveals the intensification role of binary typhoons in extreme precipitation. First, Fitow causes the maximum daily precipitation of 395.6 mm in Yuyao and Fenghua, which ranks the second daily extreme TC precipitation in Zhejiang Province in record. Two distinct intense precipitation stages are found in the precipitation process. Secondly, such intense and continuous rainfall during and after Fitow’s landfall is mainly due to the existence of Super Typhoon Danas. In the first stage of the severe precipitation the interaction of the binary tropical cyclones contributes to the extremity, causing Fitow to move much faster than before. Moreover, Danas transports about 79% moisture to the raining region, acting as an important contributor to the extreme precipitation over the southern coast of Hangzhou Bay. In the second stage, as the circulation of Typhoon Fitow almost dissipates, the combined interaction of Super Typhoon Danas and cold air causes the occurrence of the extreme precipitation.
By using the surface observational data, typhoon track data and ECMWF global reanalysis data, as well as the objective synoptic analysis technique (OSAT), tropical cyclone (TC) track similarity area index (TSAI) and the airflow trajectory model (HYSPLIT4.9), this paper analyzes the characteristics and the causes of the extreme precipitation created by the Severe Typhoon Fitow over the coastal region of Southeast China, and reveals the intensification role of binary typhoons in extreme precipitation. First, Fitow causes the maximum daily precipitation of 395.6 mm in Yuyao and Fenghua, which ranks the second daily extreme TC precipitation in Zhejiang Province in record. Two distinct intense precipitation stages are found in the precipitation process. Secondly, such intense and continuous rainfall during and after Fitow’s landfall is mainly due to the existence of Super Typhoon Danas. In the first stage of the severe precipitation the interaction of the binary tropical cyclones contributes to the extremity, causing Fitow to move much faster than before. Moreover, Danas transports about 79% moisture to the raining region, acting as an important contributor to the extreme precipitation over the southern coast of Hangzhou Bay. In the second stage, as the circulation of Typhoon Fitow almost dissipates, the combined interaction of Super Typhoon Danas and cold air causes the occurrence of the extreme precipitation.
2016, 42(2):166-173.
DOI: 10.7519/j.issn.1000-0526.2016.02.004
Abstract:
By using the surface observational data, typhoon track data and ECMWF global reanalysis data, as well as the objective synoptic analysis technique (OSAT), tropical cyclone (TC) track similarity area index (TSAI) and the airflow trajectory model (HYSPLIT4.9), this paper analyzes the characteristics and the causes of the extreme precipitation created by the Severe Typhoon Fitow over the coastal region of Southeast China, and reveals the intensification role of binary typhoons in extreme precipitation. First, Fitow causes the maximum daily precipitation of 395.6 mm in Yuyao and Fenghua, which ranks the second daily extreme TC precipitation in Zhejiang Province in record. Two distinct intense precipitation stages are found in the precipitation process. Secondly, such intense and continuous rainfall during and after Fitow’s landfall is mainly due to the existence of Super Typhoon Danas. In the first stage of the severe precipitation the interaction of the binary tropical cyclones contributes to the extremity, causing Fitow to move much faster than before. Moreover, Danas transports about 79% moisture to the raining region, acting as an important contributor to the extreme precipitation over the southern coast of Hangzhou Bay. In the second stage, as the circulation of Typhoon Fitow almost dissipates, the combined interaction of Super Typhoon Danas and cold air causes the occurrence of the extreme precipitation.
By using the surface observational data, typhoon track data and ECMWF global reanalysis data, as well as the objective synoptic analysis technique (OSAT), tropical cyclone (TC) track similarity area index (TSAI) and the airflow trajectory model (HYSPLIT4.9), this paper analyzes the characteristics and the causes of the extreme precipitation created by the Severe Typhoon Fitow over the coastal region of Southeast China, and reveals the intensification role of binary typhoons in extreme precipitation. First, Fitow causes the maximum daily precipitation of 395.6 mm in Yuyao and Fenghua, which ranks the second daily extreme TC precipitation in Zhejiang Province in record. Two distinct intense precipitation stages are found in the precipitation process. Secondly, such intense and continuous rainfall during and after Fitow’s landfall is mainly due to the existence of Super Typhoon Danas. In the first stage of the severe precipitation the interaction of the binary tropical cyclones contributes to the extremity, causing Fitow to move much faster than before. Moreover, Danas transports about 79% moisture to the raining region, acting as an important contributor to the extreme precipitation over the southern coast of Hangzhou Bay. In the second stage, as the circulation of Typhoon Fitow almost dissipates, the combined interaction of Super Typhoon Danas and cold air causes the occurrence of the extreme precipitation.
2016, 42(2):174-182.
DOI: 10.7519/j.issn.1000-0526.2016.02.005
Abstract:
Using conventional observational data, surface meteorological observation data and Doppler radar data, the weather characteristics and causes of the gust front in North China on 4 August 2013 are analyzed. The results indicate that the configuration of ground front and forwardtilting trough is the favorable largescale circulation background of the gust front. Between the outflow cold air of surface mesoscale high and environment wind forms a mesoscale convergence line, which makes the convective activity get intensified, causing new thunderstorms to generate or be strengthened. In the mature stage, squall line has distinct characteristics, and develops to the right. At first, the gust front forms in front of severe thunderstorms of the squall line. The stronger the squall line, the stronger the gust front. The maintainance of the gust front relies mainly on the continued sinking airflow of the storm. The gust front weakens after the sinking airflow drops off. Meteorological elements have dramatic changes as the squall line and gust front are passing through the area. When the system develops stronger, the variation of meteorological elements of gust front is greater than that of squall line, but is weaker in the rest time. After the squall line gets weakened, the gust front still also maintains for a period of time, which needs to be observed more carefully.
Using conventional observational data, surface meteorological observation data and Doppler radar data, the weather characteristics and causes of the gust front in North China on 4 August 2013 are analyzed. The results indicate that the configuration of ground front and forwardtilting trough is the favorable largescale circulation background of the gust front. Between the outflow cold air of surface mesoscale high and environment wind forms a mesoscale convergence line, which makes the convective activity get intensified, causing new thunderstorms to generate or be strengthened. In the mature stage, squall line has distinct characteristics, and develops to the right. At first, the gust front forms in front of severe thunderstorms of the squall line. The stronger the squall line, the stronger the gust front. The maintainance of the gust front relies mainly on the continued sinking airflow of the storm. The gust front weakens after the sinking airflow drops off. Meteorological elements have dramatic changes as the squall line and gust front are passing through the area. When the system develops stronger, the variation of meteorological elements of gust front is greater than that of squall line, but is weaker in the rest time. After the squall line gets weakened, the gust front still also maintains for a period of time, which needs to be observed more carefully.
2016, 42(2):183-191.
DOI: 10.7519/j.issn.1000-0526.2016.02.006
Abstract:
Based on available observation data of Zhejiang Province for the period from 1981 to 2013, temporal and spatial distribution characteristics of winter haze in Zhejiang Province were analyzed. The results show that haze days have increased significantly since the mid1980s. Haze days in the northern and western part of the province are much more than the south and the east, also more in the basin and plain than on the hills and islands. The division of the haze distribution pattern is obtained according to the Kmeans clustering analysis, which shows the pattern can be divided into two categories. The first category accounts for 62% of the total haze, most of which happens in December, while most of the second category usually appears in January and December. In the end, according to the NCEP/NCAR reanalysis data, the different atmospheric circulation features, including the strength of cold high, vertical velocity and the distribution of water vapor, are discussed for the two kinds of haze patterns respectively. It is found that Zhejiang Province is controlled by cold high from northern China and the sinking airflow in the first haze pattern. In the second haze pattern, however, the cold high has transformed, and the sinking flow is also weakened, which makes air move slowly, so it is hard for pollutants to dissipate.
Based on available observation data of Zhejiang Province for the period from 1981 to 2013, temporal and spatial distribution characteristics of winter haze in Zhejiang Province were analyzed. The results show that haze days have increased significantly since the mid1980s. Haze days in the northern and western part of the province are much more than the south and the east, also more in the basin and plain than on the hills and islands. The division of the haze distribution pattern is obtained according to the Kmeans clustering analysis, which shows the pattern can be divided into two categories. The first category accounts for 62% of the total haze, most of which happens in December, while most of the second category usually appears in January and December. In the end, according to the NCEP/NCAR reanalysis data, the different atmospheric circulation features, including the strength of cold high, vertical velocity and the distribution of water vapor, are discussed for the two kinds of haze patterns respectively. It is found that Zhejiang Province is controlled by cold high from northern China and the sinking airflow in the first haze pattern. In the second haze pattern, however, the cold high has transformed, and the sinking flow is also weakened, which makes air move slowly, so it is hard for pollutants to dissipate.
7 Climate Characteristics and Impact Factors of LowVisibility
Heavy Fog on Jiangsu Coast Expressway
2016, 42(2):192-202.
DOI: 10.7519/j.issn.1000-0526.2016.02.007
Abstract:
This paper analyzed the dense fogs with low visibility (＜0.5 km) that occurred from June 2012 to June 2014 on the Jiangsu Coast Expressway, and investigated the climate characteristics, meteorological elements and main circulation situation of these dense fogs with low visibility. The results indicated that there are significant differences in the monthly frequency of the dense fogs. Fogs occur frequently from March to June, and also from December to the next February. The frequency of the dense fog in spring and winter is higher than that in summer and autumn. The peak of the low visibility usually appears during 03:00-05:00 BT in the early morning, and dissipates at around 08:00 BT. If the visibility is lower than 0.5 km, the relative humidity increases to 97%, temperature is 0-4℃, wind speed decreases to less than 2 m·s-1, and wind direction is between ENE and SSE, then the visibility can further decrease to less than 0.2 km. The statistical analysis of the circulation background based on 150366 samples indicates that the low visibility in the northern and central section of the expressway is closely related to prefrontal fog. This section is located in the forepart of the cold front, and the warm sector exists in the midlow level part. The low visibility of the whole expressway is due to the advection fog and radiation fog. The radiation fog exists in the downdrafts of upper air, and the weak pressure field or the high pressure moves to the south on the surface. The advection fog is in the region of thermal advection in the midlow troposphere and behind the highpressure system entering the sea or at the east side of the inverted trough, while southeast and east winds are blowing on the surface. Before the dense fog (the visibility＜0.2 km) comes, there is a largeamplitude oscillation with obvious “trunklike” fluctuating forepart in terms of the visibility on the Jiangsu Coast Expressway. This feature provides a basis for monitoring and warning of the dense fog with visibility below 0.2 km.
This paper analyzed the dense fogs with low visibility (＜0.5 km) that occurred from June 2012 to June 2014 on the Jiangsu Coast Expressway, and investigated the climate characteristics, meteorological elements and main circulation situation of these dense fogs with low visibility. The results indicated that there are significant differences in the monthly frequency of the dense fogs. Fogs occur frequently from March to June, and also from December to the next February. The frequency of the dense fog in spring and winter is higher than that in summer and autumn. The peak of the low visibility usually appears during 03:00-05:00 BT in the early morning, and dissipates at around 08:00 BT. If the visibility is lower than 0.5 km, the relative humidity increases to 97%, temperature is 0-4℃, wind speed decreases to less than 2 m·s-1, and wind direction is between ENE and SSE, then the visibility can further decrease to less than 0.2 km. The statistical analysis of the circulation background based on 150366 samples indicates that the low visibility in the northern and central section of the expressway is closely related to prefrontal fog. This section is located in the forepart of the cold front, and the warm sector exists in the midlow level part. The low visibility of the whole expressway is due to the advection fog and radiation fog. The radiation fog exists in the downdrafts of upper air, and the weak pressure field or the high pressure moves to the south on the surface. The advection fog is in the region of thermal advection in the midlow troposphere and behind the highpressure system entering the sea or at the east side of the inverted trough, while southeast and east winds are blowing on the surface. Before the dense fog (the visibility＜0.2 km) comes, there is a largeamplitude oscillation with obvious “trunklike” fluctuating forepart in terms of the visibility on the Jiangsu Coast Expressway. This feature provides a basis for monitoring and warning of the dense fog with visibility below 0.2 km.
2016, 42(2):203-212.
DOI: 10.7519/j.issn.1000-0526.2016.02.008
Abstract:
A continuous air pollution event which occurred in Shanghai during 4-9 March 2013 was investigated. The main features of air pollution transportation and formation were preliminary discussed by using the hourly observation data of PM2.5 and PM10, conventional weather data, data from the groundbased Micro Pulse Lidar (MPL_4B), data from FY3A satellite and NCEP (1°×1°) reanalysis data. The results show that the pollution event was mainly influenced by the weather condition in upper and lower levels. The northwest wind after the trough, the stable stratification and the weak pressure field made air pollutants difficult to disperse. The northwest wind at 850 hPa could transport the dust to Shanghai, and then the dust subsided to the ground surface. The faint wind and the stable temperature stratification near the surface provided favorable conditions for the formation and maintenance of the heavy pollution event.
A continuous air pollution event which occurred in Shanghai during 4-9 March 2013 was investigated. The main features of air pollution transportation and formation were preliminary discussed by using the hourly observation data of PM2.5 and PM10, conventional weather data, data from the groundbased Micro Pulse Lidar (MPL_4B), data from FY3A satellite and NCEP (1°×1°) reanalysis data. The results show that the pollution event was mainly influenced by the weather condition in upper and lower levels. The northwest wind after the trough, the stable stratification and the weak pressure field made air pollutants difficult to disperse. The northwest wind at 850 hPa could transport the dust to Shanghai, and then the dust subsided to the ground surface. The faint wind and the stable temperature stratification near the surface provided favorable conditions for the formation and maintenance of the heavy pollution event.
2016, 42(2):213-220.
DOI: 10.7519/j.issn.1000-0526.2016.02.009
Abstract:
According to the spatiotemporal distribution characteristics of the rainfall and the geographic features, China is divided into four rainfall areas. On this basis, we developed the different assessment methods of the intensity grade of the heavy rains for every rainfall area. At the same time, elevation, standard deviation of elevation, drainage density and soil types have been identified as import controlling factors of the torrential rain disasters, and these factors were respectively classified into different grades. The comprehensive rainstorm disaster risk assessment model is established by weighted summation of the rainfall factors and the selected controlling factors. Based on the model, we further applied GIS to evaulate the number of affected urban and rural residents and land areas in different risk levels. Compared with the previous rainstorm risk assessment models, this rainstorm risk assessment model can be applied more widely in any regional rainstorm disaster risk assessment. Moreover, this model has stronger operation ability of pre assessment, realtime assesment and postassessment by using realtime or forecast rainfall data. Finally, combined with GIS, this model can achieve quantitative evaluation of the hazardaffected bodies at the different risk levels.
According to the spatiotemporal distribution characteristics of the rainfall and the geographic features, China is divided into four rainfall areas. On this basis, we developed the different assessment methods of the intensity grade of the heavy rains for every rainfall area. At the same time, elevation, standard deviation of elevation, drainage density and soil types have been identified as import controlling factors of the torrential rain disasters, and these factors were respectively classified into different grades. The comprehensive rainstorm disaster risk assessment model is established by weighted summation of the rainfall factors and the selected controlling factors. Based on the model, we further applied GIS to evaulate the number of affected urban and rural residents and land areas in different risk levels. Compared with the previous rainstorm risk assessment models, this rainstorm risk assessment model can be applied more widely in any regional rainstorm disaster risk assessment. Moreover, this model has stronger operation ability of pre assessment, realtime assesment and postassessment by using realtime or forecast rainfall data. Finally, combined with GIS, this model can achieve quantitative evaluation of the hazardaffected bodies at the different risk levels.
2016, 42(2):221-229.
DOI: 10.7519/j.issn.1000-0526.2016.02.010
Abstract:
Using the daily precipitation and disaster census data of 76 meteorological stations in Hubei from 1960 to 2005, this paper studied the spatiotemporal distribution and disastrous laws of drought and flood. The results show that the frequent occurrence area of drought presents an eastwest zonal distribution, while the annual occurrence frequency and area of flood are significantly less than those of drought. The annual average drought and flood disasters show opposite variation trends after 1996 in which droughts were more experienced but floods became less. Both of the two disasters concentrate in summer. In addition some areas of Hubei suffered from serious drought disaster continously from 1996 to 2001. The cumulative effect of the drought disaster caused the agricultural economic loss to be leapfrog growth, reaching the maxima in 2001. The flood disastercausing intensity is quasi periodic oscillation. The damaged areas of agriculture crops and agricultural economic losses reach maximum values in the 1990s with correlation coefficient being 0.80. So, positive correlation exists between the floodaffected population and direct economic loss. The increasing speed of direct economic losses is accelerated with increasing floodaffected population, while the abilities to prevent flood disaster are also strengthened. The droughtflood abrupt alternation mainly occurs in the northwest and southeast of Hubei in summer. During sharpturn disaster processes, as drought strengthens the vulnerability of crops and causes serious economic loss in the early period, the increasing speed of agricultural economic losses is accelerated with the growth of disasteraffected areas, but the agricultural economic loss would be less than the losses separately caused by droughts or floods.
Using the daily precipitation and disaster census data of 76 meteorological stations in Hubei from 1960 to 2005, this paper studied the spatiotemporal distribution and disastrous laws of drought and flood. The results show that the frequent occurrence area of drought presents an eastwest zonal distribution, while the annual occurrence frequency and area of flood are significantly less than those of drought. The annual average drought and flood disasters show opposite variation trends after 1996 in which droughts were more experienced but floods became less. Both of the two disasters concentrate in summer. In addition some areas of Hubei suffered from serious drought disaster continously from 1996 to 2001. The cumulative effect of the drought disaster caused the agricultural economic loss to be leapfrog growth, reaching the maxima in 2001. The flood disastercausing intensity is quasi periodic oscillation. The damaged areas of agriculture crops and agricultural economic losses reach maximum values in the 1990s with correlation coefficient being 0.80. So, positive correlation exists between the floodaffected population and direct economic loss. The increasing speed of direct economic losses is accelerated with increasing floodaffected population, while the abilities to prevent flood disaster are also strengthened. The droughtflood abrupt alternation mainly occurs in the northwest and southeast of Hubei in summer. During sharpturn disaster processes, as drought strengthens the vulnerability of crops and causes serious economic loss in the early period, the increasing speed of agricultural economic losses is accelerated with the growth of disasteraffected areas, but the agricultural economic loss would be less than the losses separately caused by droughts or floods.
2016, 42(2):230-237.
DOI: 10.7519/j.issn.1000-0526.2016.02.011
Abstract:
To solve the problem of automatic classification and recognition of thunderstorm system with horizontal scale less than 50 km, four features are constructed, including the density feature of thunderstorm system, emigation rate, liquid water content and cumulative liquid water content. There are significant differences in these features between hail and shorttime intense precipitation. In addition, these features can be used to describe complex system that generates hail and shorttime heavy precipitation at the same time. In view of the relationship between cumulative liquid water content and time series, the iterative mechanism is introduced in the classification tree. Experiments show that the recognition rate of systems generating shorttime heavy precipitation is as high as 89.1% and the false positive rate is 9.5%, while the recognition rate of systems generating hail is 79.8% and the false positive rate is 3.5%. The average critical success index (CSI) reaches 80.0%.
To solve the problem of automatic classification and recognition of thunderstorm system with horizontal scale less than 50 km, four features are constructed, including the density feature of thunderstorm system, emigation rate, liquid water content and cumulative liquid water content. There are significant differences in these features between hail and shorttime intense precipitation. In addition, these features can be used to describe complex system that generates hail and shorttime heavy precipitation at the same time. In view of the relationship between cumulative liquid water content and time series, the iterative mechanism is introduced in the classification tree. Experiments show that the recognition rate of systems generating shorttime heavy precipitation is as high as 89.1% and the false positive rate is 9.5%, while the recognition rate of systems generating hail is 79.8% and the false positive rate is 3.5%. The average critical success index (CSI) reaches 80.0%.
2016, 42(2):238-245.
DOI: 10.7519/j.issn.1000-0526.2016.02.012
Abstract:
Convective clouds in YangtzeHuaihe Region are the main seeding objects of precipitation enhancement experiments in Anhui Province in summer. Unrandomized seeding operations are usually adopted using rocket launchers, artilleries or ground generators, rather than the randomized trials through strict test design due to some limited condition. Convective clouds have characteristics of short life span and considerable large local and natural variations, which add great difficulties to the objective, scientific and quantitative evaluation of the operation effects. Based on daily rainfall data of national ground stations of Anhui Province and SA Doppler Radar data of the operation areas, this paper makes a case study on the seeding effects of convective clouds in YangtzeHuaihe Region from 28 to 30 June 2012 with combination of regional historical regression statistical analysis and physical test method using Doppler Radar identification and track of cloud seeding. The results indicate that the rainfall of target area increases 37.2 mm and obtains an enhancement rate of 65.19% after seeding, with a significant level α<0.1. We identify and track seeded units according to the radar data, define appropriate control units and then compare the radar echo parameters of seeded units and control units before and after operation to give physical evidence of the operation effects.
Convective clouds in YangtzeHuaihe Region are the main seeding objects of precipitation enhancement experiments in Anhui Province in summer. Unrandomized seeding operations are usually adopted using rocket launchers, artilleries or ground generators, rather than the randomized trials through strict test design due to some limited condition. Convective clouds have characteristics of short life span and considerable large local and natural variations, which add great difficulties to the objective, scientific and quantitative evaluation of the operation effects. Based on daily rainfall data of national ground stations of Anhui Province and SA Doppler Radar data of the operation areas, this paper makes a case study on the seeding effects of convective clouds in YangtzeHuaihe Region from 28 to 30 June 2012 with combination of regional historical regression statistical analysis and physical test method using Doppler Radar identification and track of cloud seeding. The results indicate that the rainfall of target area increases 37.2 mm and obtains an enhancement rate of 65.19% after seeding, with a significant level α<0.1. We identify and track seeded units according to the radar data, define appropriate control units and then compare the radar echo parameters of seeded units and control units before and after operation to give physical evidence of the operation effects.
2016, 42(2):246-253.
DOI: 10.7519/j.issn.1000-0526.2016.02.013
Abstract:
The mediumrange forecasts are verified and compared for the models of T639, ECMWF and Japan from September to November 2015. 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 ECMWF model has a good performance in predicting the position of the ridge line of western Pacific subtropical high, while T639 model is better at predicting the position of west ridge point. The three models do well in predicting the transitions of temperature at 850 hPa, and the temperature forecast biases for southern China are smaller than for northern China. As far as Typhoon Mujigae (No.1522) is concerned, the three models show different biases in its track and intensity forecasts, especially they are weak in the intensity forecasting at the early stage of the typhoon. T639 and ECMWF perform better in forecasting mediumrange static stability weather, while ECMWF does even better than T639 when forecasting cold airs that disperse fog and haze.
The mediumrange forecasts are verified and compared for the models of T639, ECMWF and Japan from September to November 2015. 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 ECMWF model has a good performance in predicting the position of the ridge line of western Pacific subtropical high, while T639 model is better at predicting the position of west ridge point. The three models do well in predicting the transitions of temperature at 850 hPa, and the temperature forecast biases for southern China are smaller than for northern China. As far as Typhoon Mujigae (No.1522) is concerned, the three models show different biases in its track and intensity forecasts, especially they are weak in the intensity forecasting at the early stage of the typhoon. T639 and ECMWF perform better in forecasting mediumrange static stability weather, while ECMWF does even better than T639 when forecasting cold airs that disperse fog and haze.
2016, 42(2):254-260.
DOI: 10.7519/j.issn.1000-0526.2016.02.014
Abstract:
The main characteristics of the general atmospheric cirulation in November 2015 are listed as follows: There is one polar vortex centre in the Northern Hemisphere. In the midhigh latitudes, the circulation presents a threewave pattern. The average south branch trough is located around 90°E. The northwestern Pacific subtropical high is stronger than normal, located more westward. Meanwhile, monthly mean precipitation amount is 39.4 mm, which is 1.1 times more than its climatological mean. Monthly mean temperature is 4.1℃, being 1.2℃ higher than normal except the North and Northeast China. Two cold air processes and 4 severe rainfall events take place with extreme precipitation records observed at some stations in China. Moreover, the precipitation amount of Jiangnan, South China and other parts is 2-3 times more than normal. In addition, three heavy pollution weather processes are experienced during this month.
The main characteristics of the general atmospheric cirulation in November 2015 are listed as follows: There is one polar vortex centre in the Northern Hemisphere. In the midhigh latitudes, the circulation presents a threewave pattern. The average south branch trough is located around 90°E. The northwestern Pacific subtropical high is stronger than normal, located more westward. Meanwhile, monthly mean precipitation amount is 39.4 mm, which is 1.1 times more than its climatological mean. Monthly mean temperature is 4.1℃, being 1.2℃ higher than normal except the North and Northeast China. Two cold air processes and 4 severe rainfall events take place with extreme precipitation records observed at some stations in China. Moreover, the precipitation amount of Jiangnan, South China and other parts is 2-3 times more than normal. In addition, three heavy pollution weather processes are experienced during this month.
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ISSN:1000-0526 CN:11-2282/P