ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Volume 43,Issue 6,2017 Table of Contents
2017, 43(6):641-652.
DOI: 10.7519/j.issn.1000-0526.2017.06.001
Abstract:
Completely understanding the conditions and mechanisms of deep moist convection (commonly referred to as “thunderstorm” in operational forecasting) and severe convective weather (especially tornadoes) is the basis for better forecasting them. This paper first analyzes the relationships between convective available potential energy and convective inhibition energy and temperature and humidity of lifted air parcel, physical significance of convection temperature, and water vapor amounts for deep moist convection, and then further proposes the definition of significant severe convective weather in China, presenting some spatiotemporal characteristics of severe convective weather, the relationship between extreme rainfall and surface dew point temperature, the producing mechanism of convectively high winds, the physical significance of wet bulb temperature closely related to hail melting layer, the environmental conditions for supercell storms and tornadoes, and the formation mechanism of mesocyclones and tornadoes. Finally, understandings of vorticity and hodograph, and their relationship with mesocyclones and tornadoes are given. Different interpretations and threshold values of some concepts and variables listed in this paper and our understandings are provided for readers to study and compare.
Completely understanding the conditions and mechanisms of deep moist convection (commonly referred to as “thunderstorm” in operational forecasting) and severe convective weather (especially tornadoes) is the basis for better forecasting them. This paper first analyzes the relationships between convective available potential energy and convective inhibition energy and temperature and humidity of lifted air parcel, physical significance of convection temperature, and water vapor amounts for deep moist convection, and then further proposes the definition of significant severe convective weather in China, presenting some spatiotemporal characteristics of severe convective weather, the relationship between extreme rainfall and surface dew point temperature, the producing mechanism of convectively high winds, the physical significance of wet bulb temperature closely related to hail melting layer, the environmental conditions for supercell storms and tornadoes, and the formation mechanism of mesocyclones and tornadoes. Finally, understandings of vorticity and hodograph, and their relationship with mesocyclones and tornadoes are given. Different interpretations and threshold values of some concepts and variables listed in this paper and our understandings are provided for readers to study and compare.
2017, 43(6):653-664.
DOI: 10.7519/j.issn.1000-0526.2017.06.002
Abstract:
Based on the GSI assimilation system and WRFARW model, a severe rainfall event which occurred in southern China for the period in 17-18 April 2016 was simulated by the method of rapid update cycle. The experiments used radar radial wind data and other conventional data in assimilation cycle. Several kinds of forecast variables were analyzed to find how the assimilation cycles and difference data would influence the forecast result. The results showed that despite the limitation of the single type of observation, there is a certain improvement effect on the false precipitation prediction by the use of rapid update cycle. Radar radial wind data and conventional data mixing assimilation could improve the humidity and precipitation prediction skills, especially at heavy rainfall levels ETS score. Although the simulated rainfall peak value is less than real observation, the assimilation of radar radial wind data could effectively improve the vertical velocity of the squall line, so the occurrence time and intensity of heavy rainfall are much closer to the real observation.
Based on the GSI assimilation system and WRFARW model, a severe rainfall event which occurred in southern China for the period in 17-18 April 2016 was simulated by the method of rapid update cycle. The experiments used radar radial wind data and other conventional data in assimilation cycle. Several kinds of forecast variables were analyzed to find how the assimilation cycles and difference data would influence the forecast result. The results showed that despite the limitation of the single type of observation, there is a certain improvement effect on the false precipitation prediction by the use of rapid update cycle. Radar radial wind data and conventional data mixing assimilation could improve the humidity and precipitation prediction skills, especially at heavy rainfall levels ETS score. Although the simulated rainfall peak value is less than real observation, the assimilation of radar radial wind data could effectively improve the vertical velocity of the squall line, so the occurrence time and intensity of heavy rainfall are much closer to the real observation.
2017, 43(6):665-674.
DOI: 10.7519/j.issn.1000-0526.2017.06.003
Abstract:
By using the data of conventional surface and sounding observations as well as the associated NCEP FNL and GFS reanalysis data, the features of precipitation type of heavy rainsnow process in North China during 3-4 November 2012 are studied in this paper. It is found that in the periphery of lowlevel vortex, the rain and snow separatrix is identical with the 0℃ isotherm and streamline convergence zone between northerly and southerly wind at 925 hPa. However, near the center of lowlevel vortex, the rain and snow separatrix takes on a feature of anticlockwise revolving from the northwest quadrant to the center of the vortex. In the early stage of cyclone developing, snow is located at the northnortheast quadarant to northwest quadrant of the 850 hPa vortex while the precipitation type at southeast quadrant is rain. As the extratropical cyclone intensifies, temperature at the southwest quadrant of lowlevel vortex drops quickly due to the lowlevel cold advection. Therefore, the snow area gradually expands southward along the wind flow of the west side of lowlevel vortex and takes on a cyclonicshaped distribution ultimately. The temporal evolution of precipitation type depends on the temperature advection of the whole lowlevel troposphere (850-950 hPa). When there is warm temperature advection in either 900-850 hPa or 950-900 hPa level, the precipitation type may still be rain even if cold advection exists in other levels. The cold temperature advection of northwest wind at the west side of lowlevel vortex is very important to snow. When the lowlevel wind transforms to eastly wind, the lowlevel cold advection disappears, and finally, the precipitation type involves to rain.
By using the data of conventional surface and sounding observations as well as the associated NCEP FNL and GFS reanalysis data, the features of precipitation type of heavy rainsnow process in North China during 3-4 November 2012 are studied in this paper. It is found that in the periphery of lowlevel vortex, the rain and snow separatrix is identical with the 0℃ isotherm and streamline convergence zone between northerly and southerly wind at 925 hPa. However, near the center of lowlevel vortex, the rain and snow separatrix takes on a feature of anticlockwise revolving from the northwest quadrant to the center of the vortex. In the early stage of cyclone developing, snow is located at the northnortheast quadarant to northwest quadrant of the 850 hPa vortex while the precipitation type at southeast quadrant is rain. As the extratropical cyclone intensifies, temperature at the southwest quadrant of lowlevel vortex drops quickly due to the lowlevel cold advection. Therefore, the snow area gradually expands southward along the wind flow of the west side of lowlevel vortex and takes on a cyclonicshaped distribution ultimately. The temporal evolution of precipitation type depends on the temperature advection of the whole lowlevel troposphere (850-950 hPa). When there is warm temperature advection in either 900-850 hPa or 950-900 hPa level, the precipitation type may still be rain even if cold advection exists in other levels. The cold temperature advection of northwest wind at the west side of lowlevel vortex is very important to snow. When the lowlevel wind transforms to eastly wind, the lowlevel cold advection disappears, and finally, the precipitation type involves to rain.
2017, 43(6):675-685.
DOI: 10.7519/j.issn.1000-0526.2017.06.004
Abstract:
A case study of an EF2 tornado that occurred in Wenchang, Hainan on 5 June 2016 was carried out by using observation data, automatic weather station data, Haikou Doppler radar data, wind profile data and 2G high resolution visible cloud images of Fengyun Meteorological Satellite. The results showed that: (1) This tornado was triggered by a supercell, corresponding to the edge of subtropical high, front of trough at 500 hPa, shear line at 850 hPa and the south side of ground thermal low. The favorable environmental conditions for the developing of the supercell were the significant increase of vertical wind shear in 0-2 km and the lower lifting condensation level, both caused by sealand breeze, and the quick increase of CAPE with solar radiation heat. (2) Both the mesoβ scale convergence line (seabreeze front) and the outflow boundary of thunderstorm triggered and enhanced the developing of the supercell, which was on the east side of eastward squall line, spreading from east to west along the mesoβ scale convergence line, and in contrast to the average wind direction of the storm bearing layer, that is, backpropagating. Some characters of the supercell including hookshaped echo, highlevel echo overhang, mesocyclone and small scale severely shear (similar with TVS) were observed. The middle mesocyclone tornado funnel cloud was generated during extension strengthening, touchdown to low level. The tornado reached its strongest stage during the time of the small scale shear developing both upwardly and downwardly from the middle level. Tornado occurred at the maximum gradient area of weak echo reflectivity of low level. (3) The merge of sea breeze front line and sinking air outflow border of supercell, generated the breeze front located in the south of supercell, and finally a horizontal vorticity tube formed from east to west orientation. A upright vorticity tube twisted when the horizontal tube met the updraft near the weak hooklike echo, forming a lowlevel mesocyclone. The breeze front located in the south of supercell met with eastward moving gust front, and the boundary layer convergence was enhanced, favoring lowlevel mesocyclone to gain the stretch rotating acceleration, and eventually tornado formed.
A case study of an EF2 tornado that occurred in Wenchang, Hainan on 5 June 2016 was carried out by using observation data, automatic weather station data, Haikou Doppler radar data, wind profile data and 2G high resolution visible cloud images of Fengyun Meteorological Satellite. The results showed that: (1) This tornado was triggered by a supercell, corresponding to the edge of subtropical high, front of trough at 500 hPa, shear line at 850 hPa and the south side of ground thermal low. The favorable environmental conditions for the developing of the supercell were the significant increase of vertical wind shear in 0-2 km and the lower lifting condensation level, both caused by sealand breeze, and the quick increase of CAPE with solar radiation heat. (2) Both the mesoβ scale convergence line (seabreeze front) and the outflow boundary of thunderstorm triggered and enhanced the developing of the supercell, which was on the east side of eastward squall line, spreading from east to west along the mesoβ scale convergence line, and in contrast to the average wind direction of the storm bearing layer, that is, backpropagating. Some characters of the supercell including hookshaped echo, highlevel echo overhang, mesocyclone and small scale severely shear (similar with TVS) were observed. The middle mesocyclone tornado funnel cloud was generated during extension strengthening, touchdown to low level. The tornado reached its strongest stage during the time of the small scale shear developing both upwardly and downwardly from the middle level. Tornado occurred at the maximum gradient area of weak echo reflectivity of low level. (3) The merge of sea breeze front line and sinking air outflow border of supercell, generated the breeze front located in the south of supercell, and finally a horizontal vorticity tube formed from east to west orientation. A upright vorticity tube twisted when the horizontal tube met the updraft near the weak hooklike echo, forming a lowlevel mesocyclone. The breeze front located in the south of supercell met with eastward moving gust front, and the boundary layer convergence was enhanced, favoring lowlevel mesocyclone to gain the stretch rotating acceleration, and eventually tornado formed.
2017, 43(6):686-695.
DOI: 10.7519/j.issn.1000-0526.2017.06.005
Abstract:
In this article, the nonhydrostatic WRF V3.6.1 (Weather Research and Forecast) model is used to simulate Typhoon ChanHom at high resolution with three nests. The model can well simulate the development and evolution of Typhoon ChanHom as well as the precipitation that it brought to the northeast of Zhejiang. Observation data indicate that the topographic friction convergence and lifting under northeast air flow make the strong convective systems gather in the northwest of the typhoon eye in the vicinity of Zhejiang, with a lot of convective cloud cluster in the convective systems. This is an important reason for the recordbreaking rainfall in northeastern Zhejiang. The control simulation also captures these features. The precipitation system is consistent with orientation of topography, i.e. the rainfall increases on the windward side. The sensitivity experiments show that topography in the northeast area of Zhejiang plays an important role in the increment of the typhoon rainfall. By lowering the terrain, the smallscale convective systems get reduced apparently. Meanwhile, the rainfall in northeastern Zhejiang weakens as well. Thus, topography can impact the structure and evolution of these convective systems, causing the abnormal changes of precipitation. Of more importance is that Typhoon ChanHom maintained the highly symmetric structure in the vicinity of Zhejiang, with the typical eyewall and warm core structure.
In this article, the nonhydrostatic WRF V3.6.1 (Weather Research and Forecast) model is used to simulate Typhoon ChanHom at high resolution with three nests. The model can well simulate the development and evolution of Typhoon ChanHom as well as the precipitation that it brought to the northeast of Zhejiang. Observation data indicate that the topographic friction convergence and lifting under northeast air flow make the strong convective systems gather in the northwest of the typhoon eye in the vicinity of Zhejiang, with a lot of convective cloud cluster in the convective systems. This is an important reason for the recordbreaking rainfall in northeastern Zhejiang. The control simulation also captures these features. The precipitation system is consistent with orientation of topography, i.e. the rainfall increases on the windward side. The sensitivity experiments show that topography in the northeast area of Zhejiang plays an important role in the increment of the typhoon rainfall. By lowering the terrain, the smallscale convective systems get reduced apparently. Meanwhile, the rainfall in northeastern Zhejiang weakens as well. Thus, topography can impact the structure and evolution of these convective systems, causing the abnormal changes of precipitation. Of more importance is that Typhoon ChanHom maintained the highly symmetric structure in the vicinity of Zhejiang, with the typical eyewall and warm core structure.
2017, 43(6):696-704.
DOI: 10.7519/j.issn.1000-0526.2017.06.006
Abstract:
This paper analyzed structure characteristics of convective clouds over the area between the Yangtze River and the Huaihe River based on Doppler radar data during 2013-2014. The used 227 convective cloud cases are classified into nine structure types. Then, we found that the isolated cell (IC), clusters of cells (CC), nonlinear systems (NL) are the dominant convective clouds over this area, accounting for 29.1%, 18.1%, and 23.3% of the total respectively. Different structural convective clouds occur under different weather backgrounds. Isolated cell is the main convection in the trough I pattern; nonlinear system is the major convection in the trough II pattern. At the same time, other structural convective clouds also occur frequently due to the common synoptic conditions. The convective clouds detected by the CFMCW radar show higher resolution of IC, CC and NL cloud structure images and the maximum falling speeds of precipitation particles, reaching 13.3 m·s-1, 8.2 m·s-1 and 11.5 m·s-1, respectively.
This paper analyzed structure characteristics of convective clouds over the area between the Yangtze River and the Huaihe River based on Doppler radar data during 2013-2014. The used 227 convective cloud cases are classified into nine structure types. Then, we found that the isolated cell (IC), clusters of cells (CC), nonlinear systems (NL) are the dominant convective clouds over this area, accounting for 29.1%, 18.1%, and 23.3% of the total respectively. Different structural convective clouds occur under different weather backgrounds. Isolated cell is the main convection in the trough I pattern; nonlinear system is the major convection in the trough II pattern. At the same time, other structural convective clouds also occur frequently due to the common synoptic conditions. The convective clouds detected by the CFMCW radar show higher resolution of IC, CC and NL cloud structure images and the maximum falling speeds of precipitation particles, reaching 13.3 m·s-1, 8.2 m·s-1 and 11.5 m·s-1, respectively.
2017, 43(6):705-715.
DOI: 10.7519/j.issn.1000-0526.2017.06.007
Abstract:
Based on the observation and reanalysis data, the spatial mode and corresponding circulation characteristics of precipitation anomaly under pentad scale in Southern China during the 2015 flood season (from April to September) are analyzed by using the methods of empirical orthogonal function (EOF), composite analysis and significance test. The results show that the westeast reverse pattern of precipitation anomaly is the major mode in the developing phases of strong El Ni〖AKn~D〗o years and the pentad pattern in 2015 shows similar features. But the pentad scale of precipitation anomaly patterns can be divided into two types of westeast reverse patterns by using the first and third EOF mode, and they have obvious differences in upper, middle, lower levels of the troposphere. The precipitation anomaly pattern of more in east and less in west (A1) with the first EOF mode is dominated by the anticyclone activities around Philippines at the low level, but the pattern of more in east and less in west (A2) with the third EOF mode is dominated by tropical cyclone activities. The pattern of less in east and more in west (B1) with the first EOF mode is obviously affected by the moving southward of the cold air activities, but the pattern of less in east and more in west (B2) with the third EOF mode is dominated by abnormal position of the anticyclone activities around Philippines at the low level. The precipitation anomaly features of westeast reverse pattern in Southern China during the 2015 flood season are closely related to the positions of anticyclones around Philippines, tropical cyclone activities and the moving path of the cold air activities.
Based on the observation and reanalysis data, the spatial mode and corresponding circulation characteristics of precipitation anomaly under pentad scale in Southern China during the 2015 flood season (from April to September) are analyzed by using the methods of empirical orthogonal function (EOF), composite analysis and significance test. The results show that the westeast reverse pattern of precipitation anomaly is the major mode in the developing phases of strong El Ni〖AKn~D〗o years and the pentad pattern in 2015 shows similar features. But the pentad scale of precipitation anomaly patterns can be divided into two types of westeast reverse patterns by using the first and third EOF mode, and they have obvious differences in upper, middle, lower levels of the troposphere. The precipitation anomaly pattern of more in east and less in west (A1) with the first EOF mode is dominated by the anticyclone activities around Philippines at the low level, but the pattern of more in east and less in west (A2) with the third EOF mode is dominated by tropical cyclone activities. The pattern of less in east and more in west (B1) with the first EOF mode is obviously affected by the moving southward of the cold air activities, but the pattern of less in east and more in west (B2) with the third EOF mode is dominated by abnormal position of the anticyclone activities around Philippines at the low level. The precipitation anomaly features of westeast reverse pattern in Southern China during the 2015 flood season are closely related to the positions of anticyclones around Philippines, tropical cyclone activities and the moving path of the cold air activities.
2017, 43(6):716-723.
DOI: 10.7519/j.issn.1000-0526.2017.06.008
Abstract:
In this paper, the yearly tropical cyclone potential impact index (YTCPI) is used as the link to preliminarily study the method of typhoon preevaluation for annual disaster situation in China. The results of preevaluation test show that, from 1991 to 2008, the preevaluation of typhoon disaster for 1996, 1997 and 2004 was lower than the facts, and for other years matched with the actual situation well. The test results of independent samples in 2009-2013 show that, only in 2009 the preevaluation was not correct. In general, it’s feasible to preevaluate the annual disaster situation of typhoon with YTCPI index.
In this paper, the yearly tropical cyclone potential impact index (YTCPI) is used as the link to preliminarily study the method of typhoon preevaluation for annual disaster situation in China. The results of preevaluation test show that, from 1991 to 2008, the preevaluation of typhoon disaster for 1996, 1997 and 2004 was lower than the facts, and for other years matched with the actual situation well. The test results of independent samples in 2009-2013 show that, only in 2009 the preevaluation was not correct. In general, it’s feasible to preevaluate the annual disaster situation of typhoon with YTCPI index.
2017, 43(6):724-734.
DOI: 10.7519/j.issn.1000-0526.2017.06.009
Abstract:
From 26 to 28 June 2015, Central Asia vortex caused heavy rainfall in the north slope of Tianshan Mountain. Using conventional data, NCEP reanalysis data and 9 weather stations’ GPS precipitable water vapor (GPSPWV) observations from the groundbased GPS networks, this article did indepth analysis on the vapor features in this process. The results show that: (1) before precipitation, at 500 hPa, the water vapor of the Arabian Sea was transported to Central Asia vortex through the Tibetan Plateau, the vortex was obviously moistened; during precipitation, at 700 hPa, the eastward water vapor transport channel was established, which was from Bay of Bengal through the Sichuan Basin and Hexi Corridor, and the easterly airflow and the southerly (SE) airflow of vortex itself converged the vapor in the heavy rain area. So, the lower atmosphere rapidly moistened in the heavy rain area. (2) All stations GPSPWV experienced wetting process from one to three days, the water jumped once or twice before precipitation began caused by the deep low vortex, and GPS PWV jumped more than 5 mm·(4 h)-1. (3) Under the same water vapor transport and vapor convergence conditions, the stronger the GPSPWV at stations of arid areas surges, the stronger the rain intensity is. To a certain extent, the water vapor transport and convergence has certain corresponding relationship with GPSPWV surge. (4) In 4-5 h before the heavy rainfall in Urumqi caused by Central Asia vortex occurred the growth rate of GPSPWV reached more than 4 mm, and the peak value of GPSPWV was almost twice of climatic mean.
From 26 to 28 June 2015, Central Asia vortex caused heavy rainfall in the north slope of Tianshan Mountain. Using conventional data, NCEP reanalysis data and 9 weather stations’ GPS precipitable water vapor (GPSPWV) observations from the groundbased GPS networks, this article did indepth analysis on the vapor features in this process. The results show that: (1) before precipitation, at 500 hPa, the water vapor of the Arabian Sea was transported to Central Asia vortex through the Tibetan Plateau, the vortex was obviously moistened; during precipitation, at 700 hPa, the eastward water vapor transport channel was established, which was from Bay of Bengal through the Sichuan Basin and Hexi Corridor, and the easterly airflow and the southerly (SE) airflow of vortex itself converged the vapor in the heavy rain area. So, the lower atmosphere rapidly moistened in the heavy rain area. (2) All stations GPSPWV experienced wetting process from one to three days, the water jumped once or twice before precipitation began caused by the deep low vortex, and GPS PWV jumped more than 5 mm·(4 h)-1. (3) Under the same water vapor transport and vapor convergence conditions, the stronger the GPSPWV at stations of arid areas surges, the stronger the rain intensity is. To a certain extent, the water vapor transport and convergence has certain corresponding relationship with GPSPWV surge. (4) In 4-5 h before the heavy rainfall in Urumqi caused by Central Asia vortex occurred the growth rate of GPSPWV reached more than 4 mm, and the peak value of GPSPWV was almost twice of climatic mean.
2017, 43(6):735-744.
DOI: 10.7519/j.issn.1000-0526.2017.06.010
Abstract:
Same as with quantitative precipitation forecast (QPF), snowfall depth forecasting is one important operation of weather forecasting in winter, and the relationship between snowfall depth and precipitation which is called snowtoliquid ratio (SLR) abroad is an important parameter required to forecast snowfall depth. In this paper, the main research progresses in variations of SLR and its impact factors at home and aboard in recent decades are reviewed, and the SLR forecast techniques and methods are summarized and compared. Studies indicate that SLR changes obviously in temporal scale, and has seasonal and spatial distribution differences. Air temperature and relative humidity are the two most important meteorological factors affecting SLR. In addition, other meteorological factors such as pressure, vertical motion, surface wind, snowfall weight, solar radiation and snow melting also affect SLR in different degrees. With the development of prediction technology, the methods of SLR forecasting can be summarized as three categories, including climatological, statistical and physical methods. The climatological method is too simple, the application of new statistical methods could improve the prediction ability of SLR, but this method still cannot get rid of the inherent deficiencies of statistics. Comparatively, the method based on the numerical model for predicting instantaneous SLR fits the developing trend toward refinement in snowfall depth forecast in future. At present, observation data of snowfall depth are less and the observation frequency is low in China, thus it is important to effectively carry out the surface snowfall and sounding observation densely, and solve the problem of lack of observation data in the research of SLR. Besides, based on the operational numerical weather prediction model exploring the influence mechanism of meteorological factors on SLR and establishing the forecast operation system suitable for winter snowfall are the developing trend in China.
Same as with quantitative precipitation forecast (QPF), snowfall depth forecasting is one important operation of weather forecasting in winter, and the relationship between snowfall depth and precipitation which is called snowtoliquid ratio (SLR) abroad is an important parameter required to forecast snowfall depth. In this paper, the main research progresses in variations of SLR and its impact factors at home and aboard in recent decades are reviewed, and the SLR forecast techniques and methods are summarized and compared. Studies indicate that SLR changes obviously in temporal scale, and has seasonal and spatial distribution differences. Air temperature and relative humidity are the two most important meteorological factors affecting SLR. In addition, other meteorological factors such as pressure, vertical motion, surface wind, snowfall weight, solar radiation and snow melting also affect SLR in different degrees. With the development of prediction technology, the methods of SLR forecasting can be summarized as three categories, including climatological, statistical and physical methods. The climatological method is too simple, the application of new statistical methods could improve the prediction ability of SLR, but this method still cannot get rid of the inherent deficiencies of statistics. Comparatively, the method based on the numerical model for predicting instantaneous SLR fits the developing trend toward refinement in snowfall depth forecast in future. At present, observation data of snowfall depth are less and the observation frequency is low in China, thus it is important to effectively carry out the surface snowfall and sounding observation densely, and solve the problem of lack of observation data in the research of SLR. Besides, based on the operational numerical weather prediction model exploring the influence mechanism of meteorological factors on SLR and establishing the forecast operation system suitable for winter snowfall are the developing trend in China.
2017, 43(6):745-755.
DOI: 10.7519/j.issn.1000-0526.2017.06.011
Abstract:
Based on the Doppler weather radar data of Liuzhou and Guilin, and the conventional upperair and surface observation data, this paper analyzes the environmental condition and radar echo structure of the severe hailstorm which occurred in Liuzhou on 9 April 2016. The results show that: (1) The background responsible for the hailstorm includes intense heatingup of the surface which led to the development of thermal depression in the lower atmosphere, the developing eastward cold temperature trough in the midlevel, and an upperlevel jet stream above the convective location. The convective clouds triggered by surface dryline and the mesoscale convergence line evolved into supercells under the influence of the unstable stratification and significant vertical wind shear. (2) The lowlevel reflectivity of the supercell showed a typical hook echo or inverted Vnotch. Along the inflow direction and through the strongest echo, the reflectivity showed typical BWER, overhanging echo and echo wall. The strongest echo was within a vertical narrow zone along the echo wall and the value got to 65 dBz. The corresponding radial velocity in the lower atmosphere had a strong mesocyclone with rotation speed reaching 24 m·s-1. The development and maintenance of mesocyclone made the supercell storm develop and maintain. (3) Maximum reflectivity reaches 60 dBz, strong echo over 50 dBz extending to the height of -30℃ layer, VIL value over 60 kg·m-2 and VIL density over 5.0 g·m-3, mesocyclone in moderate or severe intensity can be taken as the early warning indicator of severe hail.
Based on the Doppler weather radar data of Liuzhou and Guilin, and the conventional upperair and surface observation data, this paper analyzes the environmental condition and radar echo structure of the severe hailstorm which occurred in Liuzhou on 9 April 2016. The results show that: (1) The background responsible for the hailstorm includes intense heatingup of the surface which led to the development of thermal depression in the lower atmosphere, the developing eastward cold temperature trough in the midlevel, and an upperlevel jet stream above the convective location. The convective clouds triggered by surface dryline and the mesoscale convergence line evolved into supercells under the influence of the unstable stratification and significant vertical wind shear. (2) The lowlevel reflectivity of the supercell showed a typical hook echo or inverted Vnotch. Along the inflow direction and through the strongest echo, the reflectivity showed typical BWER, overhanging echo and echo wall. The strongest echo was within a vertical narrow zone along the echo wall and the value got to 65 dBz. The corresponding radial velocity in the lower atmosphere had a strong mesocyclone with rotation speed reaching 24 m·s-1. The development and maintenance of mesocyclone made the supercell storm develop and maintain. (3) Maximum reflectivity reaches 60 dBz, strong echo over 50 dBz extending to the height of -30℃ layer, VIL value over 60 kg·m-2 and VIL density over 5.0 g·m-3, mesocyclone in moderate or severe intensity can be taken as the early warning indicator of severe hail.
2017, 43(6):756-761.
DOI: 10.7519/j.issn.1000-0526.2017.06.012
Abstract:
In 2008, the thick icecoating caused by the severe freezing rain covered power transmission line in Zhejiang, leading to enormous damages to Zhejiang power grid. However, only one third of the weather stations observed the glaze with a short duration. In this paper, two severe freezing rain processes which occurred in 2008 and 2013 were analyzed using the global reanalysis data ERAInterim and the disaster records of icecoating on Zhejiang power grid. The results show that there are three layers of coldwarmcold with the warm layer’s temperature above 0℃ during the heavy freezing rain process in Zhejiang Province. In Zhejiang, the liquid water falling from the warm layer would be frozen into ice particles because the temperature in warm layer is lower and the thickness of the bottom ice layer is thicker. Sometimes, the ground temperature is above 0℃, so rain would be observed at weather stations during freezing rain. However, the thickness of bottom ice layer become thinner at high elevation, then tiny liquid water can be frozen into ice particles after it passes through the bottom ice layer. The freezing rain can be found mostly above 400 m elevation of central Zhejiang and above 600 m elevation of southern Zhejiang. According to the freezing rain characteristics in Zhejiang, the falling zone of freezing rain can be calculated based on the global reanalysis data, and the results match the disaster records of icecoating well. In general, this is a new method for freezing rain monitoring and forecasting, especially for some mountainous provinces like Zhejiang.
In 2008, the thick icecoating caused by the severe freezing rain covered power transmission line in Zhejiang, leading to enormous damages to Zhejiang power grid. However, only one third of the weather stations observed the glaze with a short duration. In this paper, two severe freezing rain processes which occurred in 2008 and 2013 were analyzed using the global reanalysis data ERAInterim and the disaster records of icecoating on Zhejiang power grid. The results show that there are three layers of coldwarmcold with the warm layer’s temperature above 0℃ during the heavy freezing rain process in Zhejiang Province. In Zhejiang, the liquid water falling from the warm layer would be frozen into ice particles because the temperature in warm layer is lower and the thickness of the bottom ice layer is thicker. Sometimes, the ground temperature is above 0℃, so rain would be observed at weather stations during freezing rain. However, the thickness of bottom ice layer become thinner at high elevation, then tiny liquid water can be frozen into ice particles after it passes through the bottom ice layer. The freezing rain can be found mostly above 400 m elevation of central Zhejiang and above 600 m elevation of southern Zhejiang. According to the freezing rain characteristics in Zhejiang, the falling zone of freezing rain can be calculated based on the global reanalysis data, and the results match the disaster records of icecoating well. In general, this is a new method for freezing rain monitoring and forecasting, especially for some mountainous provinces like Zhejiang.
2017, 43(6):762-768.
DOI: 10.7519/j.issn.1000-0526.2017.06.013
Abstract:
The main characteristics of the general atmospheric circulation are as follows. There was one polar vortex center in the Northern Hemisphere, stronger than usual. The circulation in Eurasian middlehigh latitudes showed a fourwave pattern. The strength of Western Pacific subtropical high was a little weaker than normal. While the south branch trough was a little stronger than normal. The monthly mean temperature was 4.5℃, 0.4℃ higher than normal and the monthly mean precipitation amount was 36.2 mm which is more than normal by 22.7%. Two waves of cold air processes happened in this month, and three regional torrential rain processes occurred during the same period. There were mainly two dust weather events seen in the northern part of China. Besides, severe convection weather appeared in Jiangsu and Hunan.
The main characteristics of the general atmospheric circulation are as follows. There was one polar vortex center in the Northern Hemisphere, stronger than usual. The circulation in Eurasian middlehigh latitudes showed a fourwave pattern. The strength of Western Pacific subtropical high was a little weaker than normal. While the south branch trough was a little stronger than normal. The monthly mean temperature was 4.5℃, 0.4℃ higher than normal and the monthly mean precipitation amount was 36.2 mm which is more than normal by 22.7%. Two waves of cold air processes happened in this month, and three regional torrential rain processes occurred during the same period. There were mainly two dust weather events seen in the northern part of China. Besides, severe convection weather appeared in Jiangsu and Hunan.
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ISSN:1000-0526 CN:11-2282/P