Volume 48,Issue 2,2020 Table of Contents
2020, 48(2):147-153.
Abstract:
The rainfall observation data of 2590 hours from the Parsivel laser disdrometers, tipping bucket rain gauges, and weighing rain gauges of Nanjing Meteorological Service in Jiangning Station during 2014-2018 are collected, and the performance of the Parsivel laser disdrometer for rainfall and snowfall measurement is discussed. The results show that compared with the results of the weighing rain gauge, both rainfall duration and total accumulated rainfall measured by the tipping rain gauge are lower, while the rainfall duration measured by the laser disdrometer is lower, but the total accumulated rainfall is 15.07% higher. The laser disdrometer can track the change of rain intensity effectively, but the rain intensity tends to be underestimated when the rain is light (<2.5 mm h-1), and overestimated for different degrees when the rain is heavy (≥2.5 mmm h-1). 〖JP2〗The tipping bucket rain gauge is unable to measure snowfall effectively, while the laser disdrometer can monitor the change of snowfall effectively, but it overestimates the equivalent precipitation intensity due to its limitation of measurement principle.The performance of laser disdrometer did not deteriorate with the increase of installation time from the data of 5 years.〖JP〗
The rainfall observation data of 2590 hours from the Parsivel laser disdrometers, tipping bucket rain gauges, and weighing rain gauges of Nanjing Meteorological Service in Jiangning Station during 2014-2018 are collected, and the performance of the Parsivel laser disdrometer for rainfall and snowfall measurement is discussed. The results show that compared with the results of the weighing rain gauge, both rainfall duration and total accumulated rainfall measured by the tipping rain gauge are lower, while the rainfall duration measured by the laser disdrometer is lower, but the total accumulated rainfall is 15.07% higher. The laser disdrometer can track the change of rain intensity effectively, but the rain intensity tends to be underestimated when the rain is light (<2.5 mm h-1), and overestimated for different degrees when the rain is heavy (≥2.5 mmm h-1). 〖JP2〗The tipping bucket rain gauge is unable to measure snowfall effectively, while the laser disdrometer can monitor the change of snowfall effectively, but it overestimates the equivalent precipitation intensity due to its limitation of measurement principle.The performance of laser disdrometer did not deteriorate with the increase of installation time from the data of 5 years.〖JP〗
2020, 48(2):154-162.
Abstract:
It is necessary for further making use of the measurements to conduct the comprehensive comparison of wind profiler horizontal wind against radiosonde data. Based on the 5year collocated wind speed data from radiosondes and wind profilers in Beijing, the wind profiler data are carefully analyzed, including total average, diurnal and annual variations, different sky conditions. The results show that the root mean square error of 5year average 〖WTBX〗U〖WTBZ〗component was from 2.2 to 5.0 m/s, the 〖WTBX〗V〖WTBZ〗component from 2.3 to 3.6 m/s, and the 〖WTBX〗U〖WTBZ〗component and 〖WTBX〗V〖WTBZ〗component minimum deviation occurred at 850 hPa. The 〖WTBX〗U〖WTBZ〗component average error of different heights was negative, which indicates the wind profiler 〖WTBX〗U〖WTBZ〗component wind speed is smaller than that of balloon sounding, and the absolute value of error increased with height. The 〖WTBX〗V〖WTBZ〗component average errors were negative only at 700 hPa. The similarity of 〖WTBX〗U〖WTBZ〗component at 500 hPa was the best and that of 〖WTBX〗V〖WTBZ〗 component wind at 850 hPa was the best. On average, the wind profiler wind was closer to balloon sounding at 850 hPa and 700 hPa. The errors in the 〖WTBX〗U〖WTBZ〗 and 〖WTBX〗V〖WTBZ〗 components at 14:00 were relatively smaller than those at 08:00 and 20:00, which was related to the strong atmospheric turbulence at noon. The errors were relatively small when the amount of clouds was large, and large when the amount of clouds was small (especially in clear sky). which indicates the wind profiler is sensitive to humidity. The 〖WTBX〗U〖WTBZ〗 and 〖WTBX〗V〖WTBZ〗 components have little difference and good similarity with balloon sounding in summer or summer half year, especially in June and July, and large difference and bad similarity in winter or winter half year, especially in December and January. This should be paid enough attention in forecast operation use and scientific researches.
It is necessary for further making use of the measurements to conduct the comprehensive comparison of wind profiler horizontal wind against radiosonde data. Based on the 5year collocated wind speed data from radiosondes and wind profilers in Beijing, the wind profiler data are carefully analyzed, including total average, diurnal and annual variations, different sky conditions. The results show that the root mean square error of 5year average 〖WTBX〗U〖WTBZ〗component was from 2.2 to 5.0 m/s, the 〖WTBX〗V〖WTBZ〗component from 2.3 to 3.6 m/s, and the 〖WTBX〗U〖WTBZ〗component and 〖WTBX〗V〖WTBZ〗component minimum deviation occurred at 850 hPa. The 〖WTBX〗U〖WTBZ〗component average error of different heights was negative, which indicates the wind profiler 〖WTBX〗U〖WTBZ〗component wind speed is smaller than that of balloon sounding, and the absolute value of error increased with height. The 〖WTBX〗V〖WTBZ〗component average errors were negative only at 700 hPa. The similarity of 〖WTBX〗U〖WTBZ〗component at 500 hPa was the best and that of 〖WTBX〗V〖WTBZ〗 component wind at 850 hPa was the best. On average, the wind profiler wind was closer to balloon sounding at 850 hPa and 700 hPa. The errors in the 〖WTBX〗U〖WTBZ〗 and 〖WTBX〗V〖WTBZ〗 components at 14:00 were relatively smaller than those at 08:00 and 20:00, which was related to the strong atmospheric turbulence at noon. The errors were relatively small when the amount of clouds was large, and large when the amount of clouds was small (especially in clear sky). which indicates the wind profiler is sensitive to humidity. The 〖WTBX〗U〖WTBZ〗 and 〖WTBX〗V〖WTBZ〗 components have little difference and good similarity with balloon sounding in summer or summer half year, especially in June and July, and large difference and bad similarity in winter or winter half year, especially in December and January. This should be paid enough attention in forecast operation use and scientific researches.
2020, 48(2):163-170.
Abstract:
A selfdeveloped transmission system is introduced from three aspects: measuring principles, composition structure and calculation procedures. The white LED light source is used in this system, and its divergence angle is about 1 mrad. Variation of the light source is compensated by the integrating sphere, which can split the beam. The full facula is received by the aspherical mirror. The relative deviation between the transmission system and the nephelometer is less than 10% from the 2 km to 10 km. Influencing factors of measurement performance are analyzed from measuring principles and calculation procedures. The results show that the main factors affecting the measurement performance of the system are the accuracy of the standard, the linearity of measurement, and the stability of the system. At the same time, the assessment methods and the data of calibration accuracy, measurement linearity, and system stability are given, which verify the measurement performance of the system.
A selfdeveloped transmission system is introduced from three aspects: measuring principles, composition structure and calculation procedures. The white LED light source is used in this system, and its divergence angle is about 1 mrad. Variation of the light source is compensated by the integrating sphere, which can split the beam. The full facula is received by the aspherical mirror. The relative deviation between the transmission system and the nephelometer is less than 10% from the 2 km to 10 km. Influencing factors of measurement performance are analyzed from measuring principles and calculation procedures. The results show that the main factors affecting the measurement performance of the system are the accuracy of the standard, the linearity of measurement, and the stability of the system. At the same time, the assessment methods and the data of calibration accuracy, measurement linearity, and system stability are given, which verify the measurement performance of the system.
2020, 48(2):171-177.
Abstract:
The millimeter wave radar was introduced into the Ningbo Beilun Port area in the late 2016, as a new technique of sea fog monitoring. Based on the visibility monitoring data of several regional automatic stations around Beilun Port from 2015 to 2018, the characteristics of sea fog distribution are summarized. Through the analysis and comparison of two lowvisibility weather cases in 2018, it is concluded that millimeter wave radar has obvious advantages in sea fog monitoring in port areas. The analysis shows that the fog days are different in different regions, the fog days monitored in coastal area are more than those in land, and also the fog days monitored in the high altitude areas were more than those in the lower altitude areas. The sea fogs in the harbor areas mainly appear in March to June and have the tendency of increasing month by month. In the case of sea fogs monitored by millimeter wave radar, the echo intensity is about -20 dBz, which can completely record the spatial distribution of fogs and their generation and elimination processes. The millimeter wave radar can clearly monitor the layered distribution of clouds and fogs.
The millimeter wave radar was introduced into the Ningbo Beilun Port area in the late 2016, as a new technique of sea fog monitoring. Based on the visibility monitoring data of several regional automatic stations around Beilun Port from 2015 to 2018, the characteristics of sea fog distribution are summarized. Through the analysis and comparison of two lowvisibility weather cases in 2018, it is concluded that millimeter wave radar has obvious advantages in sea fog monitoring in port areas. The analysis shows that the fog days are different in different regions, the fog days monitored in coastal area are more than those in land, and also the fog days monitored in the high altitude areas were more than those in the lower altitude areas. The sea fogs in the harbor areas mainly appear in March to June and have the tendency of increasing month by month. In the case of sea fogs monitored by millimeter wave radar, the echo intensity is about -20 dBz, which can completely record the spatial distribution of fogs and their generation and elimination processes. The millimeter wave radar can clearly monitor the layered distribution of clouds and fogs.
2020, 48(2):178-184.
Abstract:
The newgeneration weather radar system uses the 〖WTBX〗ZI〖WTBZ〗 relation to invert the precipitation. Different deviations emerge in different regions. During the observation of precipitation, the accuracy of quantitative estimation of precipitation may be weakened due to the influence of horizontal gusts, shortterm strong winds, echo intensity, topography, atmospheric refraction, and other factors. In this study, the precipitation is estimated by using the reflectance factor at different elevation angles of the radar basic data and the deviations between the estimated precipitation by radar inversion at different elevation angles and the rainfall data of automatic meteorological stations are compared and analyzed. According to the analysis of the deviation sources of estimated precipitation of radar and the precipitation deviation estimates, using mathematical statistics methods， it is concluded: the 2.4° estimates of precipitation own the highest linear correlation coefficient with automatic station observation and the radar estimation of precipitation in this angle is more real, and the 0.5° and 1.5° estimations affected by the topography are not applicable.
The newgeneration weather radar system uses the 〖WTBX〗ZI〖WTBZ〗 relation to invert the precipitation. Different deviations emerge in different regions. During the observation of precipitation, the accuracy of quantitative estimation of precipitation may be weakened due to the influence of horizontal gusts, shortterm strong winds, echo intensity, topography, atmospheric refraction, and other factors. In this study, the precipitation is estimated by using the reflectance factor at different elevation angles of the radar basic data and the deviations between the estimated precipitation by radar inversion at different elevation angles and the rainfall data of automatic meteorological stations are compared and analyzed. According to the analysis of the deviation sources of estimated precipitation of radar and the precipitation deviation estimates, using mathematical statistics methods， it is concluded: the 2.4° estimates of precipitation own the highest linear correlation coefficient with automatic station observation and the radar estimation of precipitation in this angle is more real, and the 0.5° and 1.5° estimations affected by the topography are not applicable.
LI Xianfeng
,
ZHANG Wei
,
LI Fen
,
HUANG Shaoping
,
DENG Weihua
,
HU Jiajun
,
LAI Liang
,
YANG Liyuan
2020, 48(2):185-194.
Abstract:
The realtime grid products are an important and necessary data sources for intelligent grid forecasting service, as the realtime grid products take the dual tasks of forecasting revision and forecasting product inspection. In order to meet the service requirements of meteorological applications and meteorological services for realtime grid products, various gird products are collected in realtime and standardized, and a WebGISbased realtime grid product application analysis platform is established using the Web techniques, such as JavaScript, HTML, CSS, etc. Based on the open source design idea, a framework of WebGIS supported by HTML5 is built by using Leaflet, Canvas and other technologies. All kinds of realtime grid products can be displayed on the same geographic information in this platform, and the display region can be conveniently switched among the whole country, provinces and different cities. The station observation data and station information from the CIMISS can be integrated and displayed in this platform, and more than ten thousand stations and over one million grid points can be easily drawn. The realtime data quality evaluation and analysis of the products are provided through the comparison and analysis between grid data and observations. Based on the grid points, the statistical analysis results (grid area and area ratio) in any region and different feature levels for any meteorological features are achieved, which are useful information for meteorological decision analysis and early warning forecast service in various disaster weather processes, such as heavy rains, high heat, severe winds, dense fogs, etc. Since the platform is put into application, it has provided great data supports for application and refinement meteorological services of all levels. As based on the national uniform data environment and parameter configuration, the platform has strong application and promotion value.
The realtime grid products are an important and necessary data sources for intelligent grid forecasting service, as the realtime grid products take the dual tasks of forecasting revision and forecasting product inspection. In order to meet the service requirements of meteorological applications and meteorological services for realtime grid products, various gird products are collected in realtime and standardized, and a WebGISbased realtime grid product application analysis platform is established using the Web techniques, such as JavaScript, HTML, CSS, etc. Based on the open source design idea, a framework of WebGIS supported by HTML5 is built by using Leaflet, Canvas and other technologies. All kinds of realtime grid products can be displayed on the same geographic information in this platform, and the display region can be conveniently switched among the whole country, provinces and different cities. The station observation data and station information from the CIMISS can be integrated and displayed in this platform, and more than ten thousand stations and over one million grid points can be easily drawn. The realtime data quality evaluation and analysis of the products are provided through the comparison and analysis between grid data and observations. Based on the grid points, the statistical analysis results (grid area and area ratio) in any region and different feature levels for any meteorological features are achieved, which are useful information for meteorological decision analysis and early warning forecast service in various disaster weather processes, such as heavy rains, high heat, severe winds, dense fogs, etc. Since the platform is put into application, it has provided great data supports for application and refinement meteorological services of all levels. As based on the national uniform data environment and parameter configuration, the platform has strong application and promotion value.
2020, 48(2):195-199.
Abstract:
This paper proposes the design idea and overall framework of the accurate and intelligent push platform for early warning information based on the Jiangxi Early Warning Release WeChat service, and builds a operational platform consisting of the operational support layer, data layer, service layer, and operational application layer to achieve the realtime release of the gridbased proximity prediction information and the targeted release of earlywarning information based on location. The earlywarning service model has shifted from “oneway push” to “twoway interaction.” The study applies a number of key technologies to support the intelligentization of the platform, including the core functions and technologies of the platform, such as LBS (LocationBased Service)based realtime warning, approaching rain conditions, early warning customization, targeted group sending, and background management. The platform is easy to operate and to use and provides users with tailored earlywarning services in real time.
This paper proposes the design idea and overall framework of the accurate and intelligent push platform for early warning information based on the Jiangxi Early Warning Release WeChat service, and builds a operational platform consisting of the operational support layer, data layer, service layer, and operational application layer to achieve the realtime release of the gridbased proximity prediction information and the targeted release of earlywarning information based on location. The earlywarning service model has shifted from “oneway push” to “twoway interaction.” The study applies a number of key technologies to support the intelligentization of the platform, including the core functions and technologies of the platform, such as LBS (LocationBased Service)based realtime warning, approaching rain conditions, early warning customization, targeted group sending, and background management. The platform is easy to operate and to use and provides users with tailored earlywarning services in real time.
2020, 48(2):200-208.
Abstract:
Based on the CMAP and GPCP precipitation data and the ERAInterim reanalysis data during 1979-2016, this study examines the relationship between midupper tropospheric temperature in the Tibetan Plateau (TP) and precipitation in the subtropical western North Pacific (WNP) during boreal summer and analyzes the associated physical processes. The results show a significant positive correlation between the TP midupper tropospheric temperature and the subtropical WNP precipitation on the interannual scale. When temperature in the midupper troposphere is high over the TP, the South Asian high is significantly enhanced and extends eastward to Japan. Meanwhile, there is an anomalous upward flow in the northern TP, and it gradually shifts northward with height, expanding eastward to Japan along anomalous westerly winds to the north of the enhanced South Asian high and moving downward in the area south of Japan. Corresponding to the anomalous downward motion to the south of Japan, there is a lowertroposphere anomalous anticyclonic circulation in the southern Japan, with the northerly wind anomalies to the east of the anomalous anticyclonic circulation, which is closely related to the anomalous cyclonicanticyclonic circulation coupling structure in the lowertropospheric WNP. This coupling structure in the subtropical WNP provids favorable dynamic and water vapor conditions for the occurrence of the subtropical WNP precipitation. This process gives a physical explanation for the relationship between the TP midupper tropospheric temperature and the subtropical WNP precipitation.
Based on the CMAP and GPCP precipitation data and the ERAInterim reanalysis data during 1979-2016, this study examines the relationship between midupper tropospheric temperature in the Tibetan Plateau (TP) and precipitation in the subtropical western North Pacific (WNP) during boreal summer and analyzes the associated physical processes. The results show a significant positive correlation between the TP midupper tropospheric temperature and the subtropical WNP precipitation on the interannual scale. When temperature in the midupper troposphere is high over the TP, the South Asian high is significantly enhanced and extends eastward to Japan. Meanwhile, there is an anomalous upward flow in the northern TP, and it gradually shifts northward with height, expanding eastward to Japan along anomalous westerly winds to the north of the enhanced South Asian high and moving downward in the area south of Japan. Corresponding to the anomalous downward motion to the south of Japan, there is a lowertroposphere anomalous anticyclonic circulation in the southern Japan, with the northerly wind anomalies to the east of the anomalous anticyclonic circulation, which is closely related to the anomalous cyclonicanticyclonic circulation coupling structure in the lowertropospheric WNP. This coupling structure in the subtropical WNP provids favorable dynamic and water vapor conditions for the occurrence of the subtropical WNP precipitation. This process gives a physical explanation for the relationship between the TP midupper tropospheric temperature and the subtropical WNP precipitation.
2020, 48(2):209-219.
Abstract:
Utilizing the TRMM precipitation and cloud feature database, the seasonal differences of vertical structure, areamean rainfall rate and spatialtemporal distribution of precipitation for convective systems with different echo top heights over the South China Sea between January 2001 and March 2012 are analyzed. The results show that the reflectivity greater than 20 dBz of shallow, relatively deep and deep convections was respectively concentrated in 4-8 km, 4-10 km, 4-14 km, respectively. The frequency of 20 dBz echo top height peaked at 9 km for shallow convections. In winter, the frequency of 20 dBz echo top height peaked at 13.5 km and 14 km respectively for relatively deep and deep convections. However, in other seasons, their peaks were further higher arriving 14.5 km and 16 km. Relatively deep and deep convections were both two main precipitation systems with large rainfall rates in the South China Sea. Relatively deep convections have stronger rainfall rates in summer and autumn, while deep convections have stronger rainfall rates in winter and spring. Winter has the least number of relatively deep convections and deep convections, while spring has the least number of shallow convections. Shallow convections tend to occur in the south of 12°N and deep convections tends to appear in the north of 12°N. Relatively deep convections develop in the south of 12°N in winter and spring, but across the South China Sea in summer and autumn. For relatively deep convection events, there is a deviationcenter of cyclonic convergence in the northern South China Sea. The southwest water vapor transport difference in the central and southern South China Sea and the different convergence of water vapor below 700 hPa are the main reasons for stronger precipitation rate in summer and autumn than in winter and spring.
Utilizing the TRMM precipitation and cloud feature database, the seasonal differences of vertical structure, areamean rainfall rate and spatialtemporal distribution of precipitation for convective systems with different echo top heights over the South China Sea between January 2001 and March 2012 are analyzed. The results show that the reflectivity greater than 20 dBz of shallow, relatively deep and deep convections was respectively concentrated in 4-8 km, 4-10 km, 4-14 km, respectively. The frequency of 20 dBz echo top height peaked at 9 km for shallow convections. In winter, the frequency of 20 dBz echo top height peaked at 13.5 km and 14 km respectively for relatively deep and deep convections. However, in other seasons, their peaks were further higher arriving 14.5 km and 16 km. Relatively deep and deep convections were both two main precipitation systems with large rainfall rates in the South China Sea. Relatively deep convections have stronger rainfall rates in summer and autumn, while deep convections have stronger rainfall rates in winter and spring. Winter has the least number of relatively deep convections and deep convections, while spring has the least number of shallow convections. Shallow convections tend to occur in the south of 12°N and deep convections tends to appear in the north of 12°N. Relatively deep convections develop in the south of 12°N in winter and spring, but across the South China Sea in summer and autumn. For relatively deep convection events, there is a deviationcenter of cyclonic convergence in the northern South China Sea. The southwest water vapor transport difference in the central and southern South China Sea and the different convergence of water vapor below 700 hPa are the main reasons for stronger precipitation rate in summer and autumn than in winter and spring.
2020, 48(2):220-228.
Abstract:
Based on the existed threedimensional convective cloud model, a homogenous freezing and heterogeneous nucleation scheme is newly implanted. Combined with a single mountain thunderstorm case, some sensitivity tests are used to investigate the impact of atmospheric ice nucleus concentration on microphysical processes and precipitation. Simulation results show: (1) The change of ice nucleus concentration will affect the dynamic field of the convective cloud and all the hydrometeors. As the concentration of ice nuclei increases, the concentration of ice crystals increases, and a large amount of latent heat is released during the condensation process, which leads to an increase in the vertical updraft. At the same time, the concentration of graupel particles in the cloud becomes larger. However, due to the limited water vapor content, each of the hydrometeors particles “races for” water vapor, the growth of cloud droplets, ice crystals and graupels is suppressed, and it is difficult to become a largersized precipitation particle. (2) The increase of ice nucleus concentration leads to the reduction of the scales of cloud droplets, which weakens the process of automatic conversion of cloud droplets into raindrops. The decrease in the mixing ratio of raindrops and cloud droplets inhibits the collection of droplets by raindrops. At the same time, smallscale graupel particles weaken the process of melting graupels into raindrops, which ultimately leads to a reduction in cumulative rainfall on the ground.
Based on the existed threedimensional convective cloud model, a homogenous freezing and heterogeneous nucleation scheme is newly implanted. Combined with a single mountain thunderstorm case, some sensitivity tests are used to investigate the impact of atmospheric ice nucleus concentration on microphysical processes and precipitation. Simulation results show: (1) The change of ice nucleus concentration will affect the dynamic field of the convective cloud and all the hydrometeors. As the concentration of ice nuclei increases, the concentration of ice crystals increases, and a large amount of latent heat is released during the condensation process, which leads to an increase in the vertical updraft. At the same time, the concentration of graupel particles in the cloud becomes larger. However, due to the limited water vapor content, each of the hydrometeors particles “races for” water vapor, the growth of cloud droplets, ice crystals and graupels is suppressed, and it is difficult to become a largersized precipitation particle. (2) The increase of ice nucleus concentration leads to the reduction of the scales of cloud droplets, which weakens the process of automatic conversion of cloud droplets into raindrops. The decrease in the mixing ratio of raindrops and cloud droplets inhibits the collection of droplets by raindrops. At the same time, smallscale graupel particles weaken the process of melting graupels into raindrops, which ultimately leads to a reduction in cumulative rainfall on the ground.
2020, 48(2):229-241.
Abstract:
Through the statistical analysis of different types of severe convective weather from April to September from 1998 to 2009 in Shanghai, a stepwise regression method is used to develop 0 to 12 hour potential forecast equations for all types of severe convective weather by using 42 convection parameters and their time variation. A new approach to convective potential forecasting based on the classification of four key convective parameters is designed. The key convective parameters are K index, SI, PWV (Precipitable Water Vapor) and θsedif85 (difference between 500 and 850 hPa in pseudo equivalent temperature), which depict the atmospheric thermal and water vapor conditions, respectively. According to the distributions of different types of convection, these four convective parameters are classified into 3 levels, and convective potential forecast equations are developed for each level, respectively. In comparison with the original equations, the forecast equations based on classified convective parameters are with dramatic increasing validity in the forecasting of thunderstorms, high winds, severe thunders and all types of convective weather. In addition, better performance would be granted with the following combinations: the classified SIbased equations for forecasting thunderstorms, classified PWVbased equations for forecasting severe thunder cases and all types of convective weather. The optimal combination method of severe convective potential forecasting based on the classification of key convection parameters has been used in routine application of numerical weather prediction model outputs.
Through the statistical analysis of different types of severe convective weather from April to September from 1998 to 2009 in Shanghai, a stepwise regression method is used to develop 0 to 12 hour potential forecast equations for all types of severe convective weather by using 42 convection parameters and their time variation. A new approach to convective potential forecasting based on the classification of four key convective parameters is designed. The key convective parameters are K index, SI, PWV (Precipitable Water Vapor) and θsedif85 (difference between 500 and 850 hPa in pseudo equivalent temperature), which depict the atmospheric thermal and water vapor conditions, respectively. According to the distributions of different types of convection, these four convective parameters are classified into 3 levels, and convective potential forecast equations are developed for each level, respectively. In comparison with the original equations, the forecast equations based on classified convective parameters are with dramatic increasing validity in the forecasting of thunderstorms, high winds, severe thunders and all types of convective weather. In addition, better performance would be granted with the following combinations: the classified SIbased equations for forecasting thunderstorms, classified PWVbased equations for forecasting severe thunder cases and all types of convective weather. The optimal combination method of severe convective potential forecasting based on the classification of key convection parameters has been used in routine application of numerical weather prediction model outputs.
2020, 48(2):242-247.
Abstract:
Identification of rainfall thresholds is crucial for debris flow forecasting and hazards mitigation. The data of 34 earthquake debris flow events and their responding rainfall processes in a typical debris flow prone region (the zone along the DujiangyanWenchuan National Highway) were collected through field investigations, interviews, and literature researches, etc. The 〖WTBX〗I〖WTBZ〗〖WTBX〗D 〖WTBZ〗relationship is established by analysis of the rainfall duration and mean rainfall intensity. A new debris flow warning classification is proposed based on the rainfall division method of the meteorological department of China and the rainfall duration of the debris flows. The rainfall events are divided into three levels: smallscale rainfall (SI), mediumlevel rainfall (MI), and largelevel rainfall (LI), and the 〖WTBX〗ID〖WTBZ〗 thresholds are improved. The results indicate: (1) The rainfall duration ranged from 2 to 53 hours; the mean rainfall intensity was in the range of 0.1 to 13.8 mm/h; and the 〖WTBX〗ID〖WTBZ〗 relationship can be expressed as 〖WTBX〗I〖WTBZ〗=5.94〖WTBX〗D〖WTBZ〗0.70. (2) The compounding〖WTBX〗 ID〖WTBZ〗 prediction model can be used for hierarchical warning, and about 80% debris flow events exceed the orange warning line, which can be expressed as 〖WTBX〗I〖WTBZ〗=10.0〖WTBX〗D〖WTBZ〗-0.56 （1 h ≤〖WTBX〗 D〖WTBZ〗 < 12 h） and 〖WTBX〗I〖WTBZ〗=4.8〖WTBX〗D〖WTBZ〗-0.26 （〖WTBX〗D〖WTBZ〗≥12 h）. (3) The improved compounding 〖WTBX〗ID〖WTBZ〗 relationship has a smaller slope and higher accuracy, and more suitable for the debris flow forecasting in the mountainous areas of the western China. The results are tested by the debris flows in the period of 2014 to 2016, which shows an acceptable accuracy. This study is intended to improve debris flow forecasting and hazards mitigation for earthquakeprone regions.
Identification of rainfall thresholds is crucial for debris flow forecasting and hazards mitigation. The data of 34 earthquake debris flow events and their responding rainfall processes in a typical debris flow prone region (the zone along the DujiangyanWenchuan National Highway) were collected through field investigations, interviews, and literature researches, etc. The 〖WTBX〗I〖WTBZ〗〖WTBX〗D 〖WTBZ〗relationship is established by analysis of the rainfall duration and mean rainfall intensity. A new debris flow warning classification is proposed based on the rainfall division method of the meteorological department of China and the rainfall duration of the debris flows. The rainfall events are divided into three levels: smallscale rainfall (SI), mediumlevel rainfall (MI), and largelevel rainfall (LI), and the 〖WTBX〗ID〖WTBZ〗 thresholds are improved. The results indicate: (1) The rainfall duration ranged from 2 to 53 hours; the mean rainfall intensity was in the range of 0.1 to 13.8 mm/h; and the 〖WTBX〗ID〖WTBZ〗 relationship can be expressed as 〖WTBX〗I〖WTBZ〗=5.94〖WTBX〗D〖WTBZ〗0.70. (2) The compounding〖WTBX〗 ID〖WTBZ〗 prediction model can be used for hierarchical warning, and about 80% debris flow events exceed the orange warning line, which can be expressed as 〖WTBX〗I〖WTBZ〗=10.0〖WTBX〗D〖WTBZ〗-0.56 （1 h ≤〖WTBX〗 D〖WTBZ〗 < 12 h） and 〖WTBX〗I〖WTBZ〗=4.8〖WTBX〗D〖WTBZ〗-0.26 （〖WTBX〗D〖WTBZ〗≥12 h）. (3) The improved compounding 〖WTBX〗ID〖WTBZ〗 relationship has a smaller slope and higher accuracy, and more suitable for the debris flow forecasting in the mountainous areas of the western China. The results are tested by the debris flows in the period of 2014 to 2016, which shows an acceptable accuracy. This study is intended to improve debris flow forecasting and hazards mitigation for earthquakeprone regions.
2020, 48(2):248-253.
Abstract:
Based on the WRF model of Jilin Province, the conventional meteorological elements such as temperature, humidity, cloud cover, and wind speed and the unconventional meteorological elements such as downward surface shortwave radiation flux, surface heat flux and albedo are calculated. The correlation between ultraviolet radiation （UV） with conventional and unconventional meteorological factors is analyzed by using the ultraviolet observation data in Changchun. Based on the observation of UV in Changchun, the UV index prediction models are established by using the same statistical modeling method, taking the conventional and unconventional meteorological elements and mixed meteorological elements as factors. The results show that the correlation between atmospheric short wave radiation and UV index is significantly higher than those of conventional meteorological factors such as temperature, cloud cover, specific humidity and wind speed. The UV index prediction equations of unconventional meteorological elements and mixed meteorological elements are superior to that of conventional meteorological elements. The UV index prediction equation based on mixed meteorological elements has little difference from that based on unconventional meteorological elements. In addition, the application of conventional meteorological elements to the establishment of seasonal UV index prediction equations, compared with the annual ultraviolet prediction equations, significantly improved the prediction effect. The application of unconventional meteorological elements to the establishment of seasonal UV index prediction equations, compared with the annual ultraviolet prediction equations, significantly improved the prediction effect.
Based on the WRF model of Jilin Province, the conventional meteorological elements such as temperature, humidity, cloud cover, and wind speed and the unconventional meteorological elements such as downward surface shortwave radiation flux, surface heat flux and albedo are calculated. The correlation between ultraviolet radiation （UV） with conventional and unconventional meteorological factors is analyzed by using the ultraviolet observation data in Changchun. Based on the observation of UV in Changchun, the UV index prediction models are established by using the same statistical modeling method, taking the conventional and unconventional meteorological elements and mixed meteorological elements as factors. The results show that the correlation between atmospheric short wave radiation and UV index is significantly higher than those of conventional meteorological factors such as temperature, cloud cover, specific humidity and wind speed. The UV index prediction equations of unconventional meteorological elements and mixed meteorological elements are superior to that of conventional meteorological elements. The UV index prediction equation based on mixed meteorological elements has little difference from that based on unconventional meteorological elements. In addition, the application of conventional meteorological elements to the establishment of seasonal UV index prediction equations, compared with the annual ultraviolet prediction equations, significantly improved the prediction effect. The application of unconventional meteorological elements to the establishment of seasonal UV index prediction equations, compared with the annual ultraviolet prediction equations, significantly improved the prediction effect.
2020, 48(2):254-262.
Abstract:
Based on the hourly rainfall data of 1162 stations in Anhui from 2005 to 2015, the spatial and temporal distribution characteristics of shortterm heavy rains are analyzed. The results show that shortterm heavy rainfall happens mainly in Tapieh Mountains and Wannan Mountains. The number of shortterm heavy rains changes in a singlepeak pattern annually, concentrated in June to August, and from October to next March, and shortterm heavy rainfall hardly happens. The diurnal change exhibits a doublepeak pattern: its stronger peak appearing from 15:00 to 19:00, and the weaker peak appearing from 06:00 to 09:00, while the two valleys around 01:00 and 12:00, respectively. Also, the capability of forecasting shortterm heavy rainfall based on the WRF model is estimated in different interpolation and assessment methods. The Threat Scores (TS), calculated in different interpolation methods, are all under 2%, and there is little difference among them. The Fractions Skill Score (FSS), a neighborhoodbased verification measure, is also used to assess the skill of forecast. The study shows that FSS varies with seasons, the space and time windows, and time bias. FSS in spring is the lowest, under 15%; it is more faintly affected by time bias, spatial and temporal neighborhoods than those in summer and autumn. In summer, the FSS curves, without temporal neighborhoods, are much similar, and obviously below those with temporal neighborhoods. In autumn, the model FSS with 1 to 2 hours later is higher than synchronous FSS, while FSS with 1 to 2 hours ahead is lower, which also happens in spring, but not so clear.
Based on the hourly rainfall data of 1162 stations in Anhui from 2005 to 2015, the spatial and temporal distribution characteristics of shortterm heavy rains are analyzed. The results show that shortterm heavy rainfall happens mainly in Tapieh Mountains and Wannan Mountains. The number of shortterm heavy rains changes in a singlepeak pattern annually, concentrated in June to August, and from October to next March, and shortterm heavy rainfall hardly happens. The diurnal change exhibits a doublepeak pattern: its stronger peak appearing from 15:00 to 19:00, and the weaker peak appearing from 06:00 to 09:00, while the two valleys around 01:00 and 12:00, respectively. Also, the capability of forecasting shortterm heavy rainfall based on the WRF model is estimated in different interpolation and assessment methods. The Threat Scores (TS), calculated in different interpolation methods, are all under 2%, and there is little difference among them. The Fractions Skill Score (FSS), a neighborhoodbased verification measure, is also used to assess the skill of forecast. The study shows that FSS varies with seasons, the space and time windows, and time bias. FSS in spring is the lowest, under 15%; it is more faintly affected by time bias, spatial and temporal neighborhoods than those in summer and autumn. In summer, the FSS curves, without temporal neighborhoods, are much similar, and obviously below those with temporal neighborhoods. In autumn, the model FSS with 1 to 2 hours later is higher than synchronous FSS, while FSS with 1 to 2 hours ahead is lower, which also happens in spring, but not so clear.
15 Causal Analysis of a Squall Line Thunderstorm Gale under Background of a Cold Vortex in North China
2020, 48(2):263-273.
Abstract:
By using the NCEP reanalysis data, conventional ground and radiosonde observation, satellite and Doppler radar data, etc., the causes why the storm and ground wind strengthen in the central North China are analyzed in detail. The results show: (1) On 5 August 2017, under the influence of a cold vortex, there was dry air infiltration in the middle and upper levels and conditional instability in North China; at 11:00, according to the revised radiosonde data in Tianjin, the CAPE reached 3184 J kg-1 and the lower level water vapor was abundant, which contributed to the occurrence of thunderstorm gale and moist convection. (2) The merger of the storm outflow boundary and the ground convergence line in the central North China and the higher surface dewpoint temperature in the southeastern North China are important reasons for the strong development of the squall line system in central and southern China. (3) The high temperature and humidity environment made the storm spread southward, and under the guidance of the northwest airflow, the storm finally moved south by east. (4) At 08:00, according to Beijing radiosonde data, the vertical wind shear of 0 to 6 km reached 3.3 m s-1 km-1; the air flow rose in the front and sank in the back. Strong vertical motion and vertical wind shear produced strong rotation, which made the squall line system have the characteristics of mesocyclone in the early stage. (5) Strong convergence in the middle layer and divergence at the storm top produced violent downdrafts. The maximum wind on the ground occurred in the development stage of mesocyclones and the merging of cold pools.
By using the NCEP reanalysis data, conventional ground and radiosonde observation, satellite and Doppler radar data, etc., the causes why the storm and ground wind strengthen in the central North China are analyzed in detail. The results show: (1) On 5 August 2017, under the influence of a cold vortex, there was dry air infiltration in the middle and upper levels and conditional instability in North China; at 11:00, according to the revised radiosonde data in Tianjin, the CAPE reached 3184 J kg-1 and the lower level water vapor was abundant, which contributed to the occurrence of thunderstorm gale and moist convection. (2) The merger of the storm outflow boundary and the ground convergence line in the central North China and the higher surface dewpoint temperature in the southeastern North China are important reasons for the strong development of the squall line system in central and southern China. (3) The high temperature and humidity environment made the storm spread southward, and under the guidance of the northwest airflow, the storm finally moved south by east. (4) At 08:00, according to Beijing radiosonde data, the vertical wind shear of 0 to 6 km reached 3.3 m s-1 km-1; the air flow rose in the front and sank in the back. Strong vertical motion and vertical wind shear produced strong rotation, which made the squall line system have the characteristics of mesocyclone in the early stage. (5) Strong convergence in the middle layer and divergence at the storm top produced violent downdrafts. The maximum wind on the ground occurred in the development stage of mesocyclones and the merging of cold pools.
2020, 48(2):274-283.
Abstract:
Based on the regular weather data, radar data and NCEP 1°×1° reanalysis data, the rainstorms occurred in Shanghai and Zhejiang Coast produced by typhoon Jongdari (1812) and typhoon Rumbia (1818) are comparatively analyzed. The results show: (1) Jongdari was guided by the easterly wind of the south subtropical high and the precipitation is concentrated on the south side. Rumbia was guided by the easterly wind of the south continental high and the precipitation evenly distributes on both sides. The rainstorm of Rumbia was wider than that of Jongdari, but the center is weaker. (2) At the late period of Jongdari, cold air intruded from the Hangzhou Bay which increased atmospheric convective instability and made precipitation increase again. The atmosphere was in a weak convective instability state at the late period of Rumbia, whose precipitation weakened gradually. (3) The water vapor distribution on both sides of Rumbia was even, and the water vapor flux was greater in range and more intensive than that of Jongdari, whose convergence height in vertical direction reached up to the upper troposphere. (4) The rainstorm center of Jongdari was located in the east wind of the southern South Asian high, which was conducive to the strengthening of highlevel divergence and strong precipitation.
Based on the regular weather data, radar data and NCEP 1°×1° reanalysis data, the rainstorms occurred in Shanghai and Zhejiang Coast produced by typhoon Jongdari (1812) and typhoon Rumbia (1818) are comparatively analyzed. The results show: (1) Jongdari was guided by the easterly wind of the south subtropical high and the precipitation is concentrated on the south side. Rumbia was guided by the easterly wind of the south continental high and the precipitation evenly distributes on both sides. The rainstorm of Rumbia was wider than that of Jongdari, but the center is weaker. (2) At the late period of Jongdari, cold air intruded from the Hangzhou Bay which increased atmospheric convective instability and made precipitation increase again. The atmosphere was in a weak convective instability state at the late period of Rumbia, whose precipitation weakened gradually. (3) The water vapor distribution on both sides of Rumbia was even, and the water vapor flux was greater in range and more intensive than that of Jongdari, whose convergence height in vertical direction reached up to the upper troposphere. (4) The rainstorm center of Jongdari was located in the east wind of the southern South Asian high, which was conducive to the strengthening of highlevel divergence and strong precipitation.
2020, 48(2):284-291.
Abstract:
Based on the conventional observation data, mesoscale intensive observation data, satellite and radar products and other data, a comprehensive analysis is made of a hailstorm occurred at the southern foot of the Qilian Mountains on 13 July 2015. The results show: During the process of the Mongolian cold eddy rotation, the cold trough that slid at the bottom moved southeastward to guide the advection of highaltitude cold air and positive vorticity, which, together with the convergence line on the ground, brought the hailstorm to the southern foot of the Qilian Mountains. The large humidity gradient in the north and south and the penetration of cold air in the middle and lower layers induced the greater instability of atmospheric stratification and promoted the stronger vertical upward movement, which provided favorable conditions for the development of severe convection weather. The commashaped hailstorm clouds in satellite images were the main mesoscale system causing hailstorm weather. The radar echo intensity map shows the hailstorm structure characteristics, and the VIL value shows a trend of sharp drops and steep increase, which has a onetoone correspondence with the hailstorm time.
Based on the conventional observation data, mesoscale intensive observation data, satellite and radar products and other data, a comprehensive analysis is made of a hailstorm occurred at the southern foot of the Qilian Mountains on 13 July 2015. The results show: During the process of the Mongolian cold eddy rotation, the cold trough that slid at the bottom moved southeastward to guide the advection of highaltitude cold air and positive vorticity, which, together with the convergence line on the ground, brought the hailstorm to the southern foot of the Qilian Mountains. The large humidity gradient in the north and south and the penetration of cold air in the middle and lower layers induced the greater instability of atmospheric stratification and promoted the stronger vertical upward movement, which provided favorable conditions for the development of severe convection weather. The commashaped hailstorm clouds in satellite images were the main mesoscale system causing hailstorm weather. The radar echo intensity map shows the hailstorm structure characteristics, and the VIL value shows a trend of sharp drops and steep increase, which has a onetoone correspondence with the hailstorm time.
2020, 48(2):292-298.
Abstract:
From 30 December 2016 to 8 January 2017, a haze weather with PM2.5 as the main pollutant lasted for several days and severe pollution appeared in most areas of Shandong Province. Based on the observational data and ERAInterim reanalysis data, the weather background and boundary layer characteristics of the process are analyzed. The results show that the condition of horizontal zonal circulation at high altitude, the weak pressure field on the ground and the typical stable weather patterns, were conducive to the continuous haze. During the process, three cold air processes appeared. The intensity of cold air affected the change of haze. Weak cold air could not destroy the inversion structure near the surface. At the same time, weak cold air transported pollutants from upstream, which was favorable for the accumulation of pollutants. Strong cold air brought strong vertical movements and destroyed the stable weather situation, which facilitated the diffusion and the removal of pollutants. Under the stable weather condition, the boundary layer height was an indicative physical quantity for the haze. The change of boundary layer height and AQI had a lag negative correlation relationship, and thus the AQI index increased when the boundary layer height decreased. The existence of an inversion layer for a long time was an important condition for the continuation of the haze. In addition, due to geographical reasons, the low layer southeast wind increased the humidity and the reduction of inversion layer top height, which both led to the increase of pollutant concentration, so to aggravate the haze.
From 30 December 2016 to 8 January 2017, a haze weather with PM2.5 as the main pollutant lasted for several days and severe pollution appeared in most areas of Shandong Province. Based on the observational data and ERAInterim reanalysis data, the weather background and boundary layer characteristics of the process are analyzed. The results show that the condition of horizontal zonal circulation at high altitude, the weak pressure field on the ground and the typical stable weather patterns, were conducive to the continuous haze. During the process, three cold air processes appeared. The intensity of cold air affected the change of haze. Weak cold air could not destroy the inversion structure near the surface. At the same time, weak cold air transported pollutants from upstream, which was favorable for the accumulation of pollutants. Strong cold air brought strong vertical movements and destroyed the stable weather situation, which facilitated the diffusion and the removal of pollutants. Under the stable weather condition, the boundary layer height was an indicative physical quantity for the haze. The change of boundary layer height and AQI had a lag negative correlation relationship, and thus the AQI index increased when the boundary layer height decreased. The existence of an inversion layer for a long time was an important condition for the continuation of the haze. In addition, due to geographical reasons, the low layer southeast wind increased the humidity and the reduction of inversion layer top height, which both led to the increase of pollutant concentration, so to aggravate the haze.
2020, 48(2):299-306.
Abstract:
Based on the formula of the ratio of the average maximum wind speed in 〖WTBX〗t〖WTBZ〗 seconds to the average maximum wind speed in one hour in the Minimum Design Load for Buildings and Other Structures of the United States, this paper deduces the conversion method between the wind speed measurement standards of EF level and F level, and converts 22 tornado cases in the BeijingTianjinHebei region from 1956 to 2016 from EF level to F level, and then according to the related guidelines for nuclear power plants and the tornado risk assessment method recommended in the Extreme Meteorological Events for Site Selection (HAD101/10), the risk degree of tornado in BeijingTianjinHebei region is quantitatively evaluated. The main conclusions are as follows: for 1/4 mile wind run, the average maximum wind speed of 122 tornado cases in BeijingTianjinHebei is lower than 3second average maximum wind speed, 2.1 m s1 lower than the average, and the higher the wind speed is, the smaller the gap is; 122 tornado cases are distributed in four grades from F0 to F3, including 31 in F0, 78 in F1, 12 in F2 and 1 in F3; in the BeijingTianjinHebei region, tornadoes occur most frequently are in Tianjin, Tangshan and Zhangjiakou, 21, 21 and 14 times, respectively, and the most severe tornadoes occur in Langfang (3); there were no strong tornadoes in Hengshui, Chengde, Baoding and Beijing; the recurrence periods of tornadoes exceeding EF1, EF2, EF3 and EF4 levels in Beijing, Tianjin and Hebei are 5.8, 10.1, 20.2 and 49.5 years respectively, and those exceeding F1, F2, F3 and F4 levels are 4.9, 13.8, 38.5 and 130.7 years, respectively; the recurrence periods of tornadoes exceeding F1, F2, F3 and F4 levels are 4.9, 13.8, 38.5 and 130.7 years; in the BeijingTianjinHebei region, the tornado design reference wind speed on the unit surface (1 km2) corresponding to the 107 probability level is 73.4 m s-1。
Based on the formula of the ratio of the average maximum wind speed in 〖WTBX〗t〖WTBZ〗 seconds to the average maximum wind speed in one hour in the Minimum Design Load for Buildings and Other Structures of the United States, this paper deduces the conversion method between the wind speed measurement standards of EF level and F level, and converts 22 tornado cases in the BeijingTianjinHebei region from 1956 to 2016 from EF level to F level, and then according to the related guidelines for nuclear power plants and the tornado risk assessment method recommended in the Extreme Meteorological Events for Site Selection (HAD101/10), the risk degree of tornado in BeijingTianjinHebei region is quantitatively evaluated. The main conclusions are as follows: for 1/4 mile wind run, the average maximum wind speed of 122 tornado cases in BeijingTianjinHebei is lower than 3second average maximum wind speed, 2.1 m s1 lower than the average, and the higher the wind speed is, the smaller the gap is; 122 tornado cases are distributed in four grades from F0 to F3, including 31 in F0, 78 in F1, 12 in F2 and 1 in F3; in the BeijingTianjinHebei region, tornadoes occur most frequently are in Tianjin, Tangshan and Zhangjiakou, 21, 21 and 14 times, respectively, and the most severe tornadoes occur in Langfang (3); there were no strong tornadoes in Hengshui, Chengde, Baoding and Beijing; the recurrence periods of tornadoes exceeding EF1, EF2, EF3 and EF4 levels in Beijing, Tianjin and Hebei are 5.8, 10.1, 20.2 and 49.5 years respectively, and those exceeding F1, F2, F3 and F4 levels are 4.9, 13.8, 38.5 and 130.7 years, respectively; the recurrence periods of tornadoes exceeding F1, F2, F3 and F4 levels are 4.9, 13.8, 38.5 and 130.7 years; in the BeijingTianjinHebei region, the tornado design reference wind speed on the unit surface (1 km2) corresponding to the 107 probability level is 73.4 m s-1。
2020, 48(2):307-312.
Abstract:
Using the daily meteorological drought index, daily precipitation and Hunan weather/climate regionalization data of 97 meteorological stations in Hunan, the extreme drought characteristics of Hunan and the potential of weather modification during extreme drought periods are studied. The results show: Hunan has considerable potential for rainfall enhancement during the extreme drought periods. The extreme drought frequency and the interdecadal variation of atmospheric precipitation in each subarea are characterized by the characteristic of less in North and greater South. The annual number of days in which rainfall may be enhanced in each area during extreme drought periods is mainly characterized by monthly differences, which is mainly concentrated from August to October. The small difference in each partition area and the number of rainincreasing days in each period in the drought period is about 16% to 20% of the drought periods. There are 11 types of extreme droughts in Hunan according to the occurrence season. The summerautumn continuous droughts have the highest occurrence frequency, which have the highest number of days in which rainfall may be enhanced.
Using the daily meteorological drought index, daily precipitation and Hunan weather/climate regionalization data of 97 meteorological stations in Hunan, the extreme drought characteristics of Hunan and the potential of weather modification during extreme drought periods are studied. The results show: Hunan has considerable potential for rainfall enhancement during the extreme drought periods. The extreme drought frequency and the interdecadal variation of atmospheric precipitation in each subarea are characterized by the characteristic of less in North and greater South. The annual number of days in which rainfall may be enhanced in each area during extreme drought periods is mainly characterized by monthly differences, which is mainly concentrated from August to October. The small difference in each partition area and the number of rainincreasing days in each period in the drought period is about 16% to 20% of the drought periods. There are 11 types of extreme droughts in Hunan according to the occurrence season. The summerautumn continuous droughts have the highest occurrence frequency, which have the highest number of days in which rainfall may be enhanced.
External LinksChina Meteorological AdministrationCMA Meteorological Observation CentreChinese Academy of Meteorological SciencesBeijing Meteorological ServiceNational Satellite Meteorological Center
You are thevisitors
Supported by:Beijing E-Tiller Technology Development Co., Ltd.
Supported by:Beijing E-Tiller Technology Development Co., Ltd.