ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Volume 38,Issue 7,2012 Table of Contents
2012, 38(7):769-778.
DOI: 10.7519/j.issn.1000-0526.2012.07.001
Abstract:
Based on upper air sounding and surface observations in winter of 2001-2010, the formation physical process of freezing rain and ice pellet at different regions are investigated. It is found that: (1) Except northern China region, the formation mechanism of freezing rain in China is mostly due to a warm rain process. In northern China region, freezing rain with melting process only accounts for 39%, but the higher latitudes, the higher ratio of melting process freezing rain. Warm layer aloft is an important characteristic of freezing rain weather. And its main functions are water vapor supply and frontal system maintaining, thus help to produce precipitation. Negative temperatures at low levels and surface could be the upmost factor for freezing rain. (2) Melting process is the main formation mechanism of ice pellet in China. Generally, cloud top of ice pellet is higher than that of freezing rain. Warm layer’s thickness and intensity of ice pellet are weaker than those of freezing rain. That is because weaker warm layer only partly makes ice crystal and snow aloft melt, thus ensure their refreezing within low levels. Wind speed at 700 hPa of ice pellet is commonly smaller than that of freezing rain, which, on the one hand, reflects the lower requirement of water vapor supply for ice pellet, and weaker warm layer aloft on the other hand. Cloud top, warm layer thickness and intensity, low level dew point depression, wind speed at 700 hPa and surface temperature are good factors to discriminate freezing rain from ice pellet, but in different regions, the effectiveness of these factors is different. The main difference of freezing rain and ice pellet in Southwest China is the surface temperature, and other factors play a secondary role due to unobvious difference of them.
Based on upper air sounding and surface observations in winter of 2001-2010, the formation physical process of freezing rain and ice pellet at different regions are investigated. It is found that: (1) Except northern China region, the formation mechanism of freezing rain in China is mostly due to a warm rain process. In northern China region, freezing rain with melting process only accounts for 39%, but the higher latitudes, the higher ratio of melting process freezing rain. Warm layer aloft is an important characteristic of freezing rain weather. And its main functions are water vapor supply and frontal system maintaining, thus help to produce precipitation. Negative temperatures at low levels and surface could be the upmost factor for freezing rain. (2) Melting process is the main formation mechanism of ice pellet in China. Generally, cloud top of ice pellet is higher than that of freezing rain. Warm layer’s thickness and intensity of ice pellet are weaker than those of freezing rain. That is because weaker warm layer only partly makes ice crystal and snow aloft melt, thus ensure their refreezing within low levels. Wind speed at 700 hPa of ice pellet is commonly smaller than that of freezing rain, which, on the one hand, reflects the lower requirement of water vapor supply for ice pellet, and weaker warm layer aloft on the other hand. Cloud top, warm layer thickness and intensity, low level dew point depression, wind speed at 700 hPa and surface temperature are good factors to discriminate freezing rain from ice pellet, but in different regions, the effectiveness of these factors is different. The main difference of freezing rain and ice pellet in Southwest China is the surface temperature, and other factors play a secondary role due to unobvious difference of them.
2012, 38(7):779-785.
DOI: 10.7519/j.issn.1000-0526.2012.07.002
Abstract:
Based on the conventional observational data and NCEP 1°×1° reanalysis data, the rainfall distribution of zonal shear line heavy rain was refinedly analyzed. The results show that, although the location of low level shear line is important to the distribution of heavy rain, it is not the unique decisive factor to the distribution. The spatial structure of affecting system and the interaction between cold and warm air are essential to the heavy rain fine forecast. With the cold air invasion from the northeast region of China and northeast wind crossing Shandong Province, there are two rainfall areas. One is related with the shear line, and the other is caused by frontal uplift of the ground northeast of the heavy rain area. When a warm low is located in the northeast region of China and 850 hPa cold center entrenched in Shandong Province and there is a strong southwest warm air flow with shear line, the rainfall area of heavy rain is located between the shear line and the stationary front in South Shandong Province. Wind convergence center is often accompanied with high humidity area, and the rainfall area is usually located in the front of high humidity area and near wind convergence center.
Based on the conventional observational data and NCEP 1°×1° reanalysis data, the rainfall distribution of zonal shear line heavy rain was refinedly analyzed. The results show that, although the location of low level shear line is important to the distribution of heavy rain, it is not the unique decisive factor to the distribution. The spatial structure of affecting system and the interaction between cold and warm air are essential to the heavy rain fine forecast. With the cold air invasion from the northeast region of China and northeast wind crossing Shandong Province, there are two rainfall areas. One is related with the shear line, and the other is caused by frontal uplift of the ground northeast of the heavy rain area. When a warm low is located in the northeast region of China and 850 hPa cold center entrenched in Shandong Province and there is a strong southwest warm air flow with shear line, the rainfall area of heavy rain is located between the shear line and the stationary front in South Shandong Province. Wind convergence center is often accompanied with high humidity area, and the rainfall area is usually located in the front of high humidity area and near wind convergence center.
2012, 38(7):786-794.
DOI: 10.7519/j.issn.1000-0526.2012.07.003
Abstract:
The authors contrasted and analyzed the spatial distribution map of hourly air column vapor content retrieved from the 63 GPS/MET monitoring stations from May to September during 2009-2011 in Shanxi, and the corresponding meteorological observation data in 459 days, and the rainstorm falling area in 42 rainstorm days, and the corresponding flow pattern configuration map, and discovered that: (1) When the horizontal gradents of the air column vapor content spatial distribution are between 25 to 40 mm/latitude(longitude), in the next 12-36 hours, the probability of rainstorm and above is 100 percent in the big value area of horizontal gradents and its neighboring 0.5-1.0 latitude and longitude range from south to north (east to west); when the horizontal gradents of the air column vapor content spatial distribution is ≥40 mm/latitude(longitude), the probability of rainstorm is 63.6 percent in the big value area and its neighboring 0.5 latitude and longitude range from south to north (east to west); (2) The rainstorm falling area appears in the south (east) or north (west) 0.5-1.0 latitude and longitude of the horizontal gradents big value area of the air column vapor content spatial distribution, different flow pattern configuration would be a different result. Using the hourly GPS/MET data and hourly automatic weather station (AWS) maximum wind speed data, and based on the different location of rainstorm appearing in the horizontal gradents big value area in air column vapor content spatial distribution map, the authors built several rainstorm conceptual models in different flow pattern configurations; under C/S construction, the authors improved rainstorm falling area 12-36 h forecasting model with the contour recognition technology, and achieved automatic operation runs, and the quasi operation run in 2011 proved good effects.
The authors contrasted and analyzed the spatial distribution map of hourly air column vapor content retrieved from the 63 GPS/MET monitoring stations from May to September during 2009-2011 in Shanxi, and the corresponding meteorological observation data in 459 days, and the rainstorm falling area in 42 rainstorm days, and the corresponding flow pattern configuration map, and discovered that: (1) When the horizontal gradents of the air column vapor content spatial distribution are between 25 to 40 mm/latitude(longitude), in the next 12-36 hours, the probability of rainstorm and above is 100 percent in the big value area of horizontal gradents and its neighboring 0.5-1.0 latitude and longitude range from south to north (east to west); when the horizontal gradents of the air column vapor content spatial distribution is ≥40 mm/latitude(longitude), the probability of rainstorm is 63.6 percent in the big value area and its neighboring 0.5 latitude and longitude range from south to north (east to west); (2) The rainstorm falling area appears in the south (east) or north (west) 0.5-1.0 latitude and longitude of the horizontal gradents big value area of the air column vapor content spatial distribution, different flow pattern configuration would be a different result. Using the hourly GPS/MET data and hourly automatic weather station (AWS) maximum wind speed data, and based on the different location of rainstorm appearing in the horizontal gradents big value area in air column vapor content spatial distribution map, the authors built several rainstorm conceptual models in different flow pattern configurations; under C/S construction, the authors improved rainstorm falling area 12-36 h forecasting model with the contour recognition technology, and achieved automatic operation runs, and the quasi operation run in 2011 proved good effects.
2012, 38(7):795-803.
DOI: 10.7519/j.issn.1000-0526.2012.07.004
Abstract:
Based on the conventional surface and intensive AWS rainfall data, satellite cloud images, and NCEP FNL global analysis datasets, the rainfall event over Hainan in autumn 2008 is studied. The results show that, interaction among the tropical depression, cold surge, and subtropical high induces the persistent low level easterly/southeasterly jet, which is an important trigger mechanism for MCS by the formation of on shore convergence and topographic lifting. The warm moist air transported by the low level jet is the main reason for the repeated development of convective instability. The strong low level convergence ahead of cold surge, latent heat release, and upper level divergence are benefitial to the developing and maintaining of tropical depression. The interaction between tropical depression and cold surge increases the baroclinicity, which would reinforce the low level northeasterly jet by quasi geostrophic and inertial oscillation processes. The strong convergence and deformation between the northeasterly and southeasterly jets result in the persistent frontogenesis. The ascending branch of direct thermal circulation forced by frontogenesis and the secondary circulation associated with low level jet are the main dynamic mechanism for the development of convective systems. And strong latent heat at low levels also leads convective systems to develop more vigorously.
Based on the conventional surface and intensive AWS rainfall data, satellite cloud images, and NCEP FNL global analysis datasets, the rainfall event over Hainan in autumn 2008 is studied. The results show that, interaction among the tropical depression, cold surge, and subtropical high induces the persistent low level easterly/southeasterly jet, which is an important trigger mechanism for MCS by the formation of on shore convergence and topographic lifting. The warm moist air transported by the low level jet is the main reason for the repeated development of convective instability. The strong low level convergence ahead of cold surge, latent heat release, and upper level divergence are benefitial to the developing and maintaining of tropical depression. The interaction between tropical depression and cold surge increases the baroclinicity, which would reinforce the low level northeasterly jet by quasi geostrophic and inertial oscillation processes. The strong convergence and deformation between the northeasterly and southeasterly jets result in the persistent frontogenesis. The ascending branch of direct thermal circulation forced by frontogenesis and the secondary circulation associated with low level jet are the main dynamic mechanism for the development of convective systems. And strong latent heat at low levels also leads convective systems to develop more vigorously.
2012, 38(7):804-813.
DOI: 10.7519/j.issn.1000-0526.2012.07.005
Abstract:
The conventional surface and upper air sounding meteorological data, the hourly precipitation data from AWS in Shaanxi Province and the NCEP 1°×1° reanalysis data were used to analyze two rainstorm processes respectively in 23-24 July 2010 (“0723”) and 28-29 July 2011 (“0728”). The results show that: the relatively stable circulation is the favorable background to the development of two major rainstorms, the low level jet has established at early period of the “0723” precipitation．For the “0728” rainstorm, jet stream was from east to west at its early period; accompanied with the formation of low level jet, the high level jet stream enhances and turns upright, then heavy precipitation occurred. The southerly flow in the east of tropical depression “Chanthu” formed a wide and strong water vapor transport channel along the periphery of the subtropical high, however, the southeast airflow in the north of tropical storm “Nock ten” merged with the southwest airflow from the Bay of Bengal and then transported to the rainstorm area during the “0728” rainstorm. Shaanxi Province is located in high energy areas of θse during the two rainstorm processes. There are invasions of the dry and cold air, and potential vorticity disturbance declines along the intensive areas of θse in the two processes of rainstorm. Temporal changes in potential vorticity and precipitation almost take place simultaneously, and the appearance of large values of potential vorticity indicates the occurrence of rainstorm.
The conventional surface and upper air sounding meteorological data, the hourly precipitation data from AWS in Shaanxi Province and the NCEP 1°×1° reanalysis data were used to analyze two rainstorm processes respectively in 23-24 July 2010 (“0723”) and 28-29 July 2011 (“0728”). The results show that: the relatively stable circulation is the favorable background to the development of two major rainstorms, the low level jet has established at early period of the “0723” precipitation．For the “0728” rainstorm, jet stream was from east to west at its early period; accompanied with the formation of low level jet, the high level jet stream enhances and turns upright, then heavy precipitation occurred. The southerly flow in the east of tropical depression “Chanthu” formed a wide and strong water vapor transport channel along the periphery of the subtropical high, however, the southeast airflow in the north of tropical storm “Nock ten” merged with the southwest airflow from the Bay of Bengal and then transported to the rainstorm area during the “0728” rainstorm. Shaanxi Province is located in high energy areas of θse during the two rainstorm processes. There are invasions of the dry and cold air, and potential vorticity disturbance declines along the intensive areas of θse in the two processes of rainstorm. Temporal changes in potential vorticity and precipitation almost take place simultaneously, and the appearance of large values of potential vorticity indicates the occurrence of rainstorm.
2012, 38(7):814-818.
DOI: 10.7519/j.issn.1000-0526.2012.07.006
Abstract:
Using surface observation, upper air sounding, satellite, Doppler radar and lightning data, synoptic scale environmental conditions and detailed mesoscale development analysis are undertaken on the severe convective system over Guangdong in the morning of April 17, 2011. Short time heavy rain, hail and squall were detected in this convective system, and results show that, the trigger of severe convective storms is the cold front, and meanwhile the local topography of the Pearl River Delta, mid level jet over Guangdong and large wind shear are considerably important in maintaining and developing of the storm. In the last, analysis and summary of subjective forecasting in this weather system are also given.
Using surface observation, upper air sounding, satellite, Doppler radar and lightning data, synoptic scale environmental conditions and detailed mesoscale development analysis are undertaken on the severe convective system over Guangdong in the morning of April 17, 2011. Short time heavy rain, hail and squall were detected in this convective system, and results show that, the trigger of severe convective storms is the cold front, and meanwhile the local topography of the Pearl River Delta, mid level jet over Guangdong and large wind shear are considerably important in maintaining and developing of the storm. In the last, analysis and summary of subjective forecasting in this weather system are also given.
7 Analysis on Dynamic Structure of Cold Wind Shear Heavy Rainstorm by Intensified Observational Data
2012, 38(7):819-827.
DOI: 10.7519/j.issn.1000-0526.2012.07.007
Abstract:
With observational data from wind profiler, Doppler weather radar, surface automatic weather station (AWS) and lightning position finder, the dynamic structure of a heavy rainstorm is analyzed to search how to follow a rainstorm case by kinds of new data. This case occurred in Qingdao, the coastal city in the southeast of Shandong Province. The results are as the following. Cold wind shear is the prevailing weather system to cause the rainstorm. Cold air comes first from the lower troposphere and then cold front becomes stationary. Wind shear is obvious below 850 hPa.There are three rainfall phases. The heaviest rainfalls with strong lightning produced when cold air bursts near wind shear in 925 hPa. Rainfall was distributed in the over lapping area between northeast wind at 925 hPa and southwest wind at 850 hPa. Heavy rainfall is in accord with wind shear. Horizontal wind is obviously different during the wind shear developing. Mesoscale cyclonical circulation that is the key factor to produce convective heavy rainfall is remarkable at the beginning of cold air bursts. But it disappeared and is replaced by the wind shear at the forming of stationary front. In the end of stationary front, the wind shear only preserves in the mid troposphere so that stable and weak rainfall can be seen. Wind profiler data are good signal for rainstorm development. Rainfall begins with southwest wind strengthening 4 hours later and wind direction turns northeast near the surface. Strong north and south winds change by turn, which is the significant features of the heavy rain. Rain ends when wind turns north in every altitude.
With observational data from wind profiler, Doppler weather radar, surface automatic weather station (AWS) and lightning position finder, the dynamic structure of a heavy rainstorm is analyzed to search how to follow a rainstorm case by kinds of new data. This case occurred in Qingdao, the coastal city in the southeast of Shandong Province. The results are as the following. Cold wind shear is the prevailing weather system to cause the rainstorm. Cold air comes first from the lower troposphere and then cold front becomes stationary. Wind shear is obvious below 850 hPa.There are three rainfall phases. The heaviest rainfalls with strong lightning produced when cold air bursts near wind shear in 925 hPa. Rainfall was distributed in the over lapping area between northeast wind at 925 hPa and southwest wind at 850 hPa. Heavy rainfall is in accord with wind shear. Horizontal wind is obviously different during the wind shear developing. Mesoscale cyclonical circulation that is the key factor to produce convective heavy rainfall is remarkable at the beginning of cold air bursts. But it disappeared and is replaced by the wind shear at the forming of stationary front. In the end of stationary front, the wind shear only preserves in the mid troposphere so that stable and weak rainfall can be seen. Wind profiler data are good signal for rainstorm development. Rainfall begins with southwest wind strengthening 4 hours later and wind direction turns northeast near the surface. Strong north and south winds change by turn, which is the significant features of the heavy rain. Rain ends when wind turns north in every altitude.
2012, 38(7):828-833.
DOI: 10.7519/j.issn.1000-0526.2012.07.008
Abstract:
The space time distribution features and large scale atmospheric circulation of the 2011 autumn rainfall in West China are analyzed to study the physical mechanisms of autumn rainfall. The results show that there were more rainy days, stronger raining processes and longer duration than normal in northern West China in September 2011. The 500 hPa circulation analysis shows that there was a quasi stationary ridge near Lake Balkhash, from which the cold air was combined constantly with the warm and humid southeast air in the southwest side of the subtropical high and with the southwest air from the Bay of Bengal. The physical analysis shows that there was a strong energy frontal zone in the north of West China, which was strengthened because the cold air from the east area entered so that the instability energy burst out, thus triggering the rainstorm in West China.
The space time distribution features and large scale atmospheric circulation of the 2011 autumn rainfall in West China are analyzed to study the physical mechanisms of autumn rainfall. The results show that there were more rainy days, stronger raining processes and longer duration than normal in northern West China in September 2011. The 500 hPa circulation analysis shows that there was a quasi stationary ridge near Lake Balkhash, from which the cold air was combined constantly with the warm and humid southeast air in the southwest side of the subtropical high and with the southwest air from the Bay of Bengal. The physical analysis shows that there was a strong energy frontal zone in the north of West China, which was strengthened because the cold air from the east area entered so that the instability energy burst out, thus triggering the rainstorm in West China.
2012, 38(7):834-840.
DOI: 10.7519/j.issn.1000-0526.2012.07.009
Abstract:
Typhoon Meranti intensified significantly after moving into the Taiwan Straits. This paper performed a survey on the intensity change of tropical cyclones with a similar track to Meranti in history and found that almost no TCs intensified. The process of the intensity change of Meranti in the Taiwan Straits is analyzed. We find that the intensity estimates provided by many typhoon forecast centers in operation are weaker than observations greatly. By using synoptic and dynamic diagnosis, we analyze the basic environment conditions of the tropical cyclone’s development when Meranti moves into the Taiwan Straits and find that the high SST in the Taiwan Straits, the abundant water vapor transport in lower and middle levels, the strong low level convergence and upper level divergence, and the intense low level positive vorticity transport provides the favorable dynamic and thermodynamic conditions for the intensification of Meranti, and the weak vertical environmental wind shear cannot inhibit the development of Meranti. These results may turn out to be meaningful references for operational TC intensity forecast.
Typhoon Meranti intensified significantly after moving into the Taiwan Straits. This paper performed a survey on the intensity change of tropical cyclones with a similar track to Meranti in history and found that almost no TCs intensified. The process of the intensity change of Meranti in the Taiwan Straits is analyzed. We find that the intensity estimates provided by many typhoon forecast centers in operation are weaker than observations greatly. By using synoptic and dynamic diagnosis, we analyze the basic environment conditions of the tropical cyclone’s development when Meranti moves into the Taiwan Straits and find that the high SST in the Taiwan Straits, the abundant water vapor transport in lower and middle levels, the strong low level convergence and upper level divergence, and the intense low level positive vorticity transport provides the favorable dynamic and thermodynamic conditions for the intensification of Meranti, and the weak vertical environmental wind shear cannot inhibit the development of Meranti. These results may turn out to be meaningful references for operational TC intensity forecast.
2012, 38(7):841-847.
DOI: 10.7519/j.issn.1000-0526.2012.07.010
Abstract:
Typhoons Chanchu (0601) and Megi (1013) make similar abrupt northward recurving movements after they enter the South China Sea from the Philippine Sea. This analysis is performed to probe the main environmental factors responsible for TCs suddenly turning. The results show that both typhoons experience similar environmental adjustment periods, which can explain TCs movement: In the first stage, a westerly trough moves eastward, forcing the subtropical high to weaken and recede from South China, making the TC moving slow down. In the second stage, the subtropical high reinforces and extends southwestward, passing by the south area to TC; when it is connected with the equatorial high, the cross equatorial flow joins the southerly wind west of the subtropical high, leading TC to move northward. Meanwhile, at higher latitudes, rather weak cold air flow intrudes southward. The further calculation confirms that steering flows change abruptly with the environmental situation, from easterly to southerly, which is principal for both Chanchu and Megi making northward turns. For autumn typhoon, Megi, the best steering flow is at lower levels than that of early summer typhoon Chanchu. In operational practice, there are many kinds of forecast information provided by different methods, models and super ensemble models, the real time modifications are necessary in accordance with environmental circulation changes.
Typhoons Chanchu (0601) and Megi (1013) make similar abrupt northward recurving movements after they enter the South China Sea from the Philippine Sea. This analysis is performed to probe the main environmental factors responsible for TCs suddenly turning. The results show that both typhoons experience similar environmental adjustment periods, which can explain TCs movement: In the first stage, a westerly trough moves eastward, forcing the subtropical high to weaken and recede from South China, making the TC moving slow down. In the second stage, the subtropical high reinforces and extends southwestward, passing by the south area to TC; when it is connected with the equatorial high, the cross equatorial flow joins the southerly wind west of the subtropical high, leading TC to move northward. Meanwhile, at higher latitudes, rather weak cold air flow intrudes southward. The further calculation confirms that steering flows change abruptly with the environmental situation, from easterly to southerly, which is principal for both Chanchu and Megi making northward turns. For autumn typhoon, Megi, the best steering flow is at lower levels than that of early summer typhoon Chanchu. In operational practice, there are many kinds of forecast information provided by different methods, models and super ensemble models, the real time modifications are necessary in accordance with environmental circulation changes.
11 The Numerical Simulation Analysis and Causes of Snowstorm Occurring in Hunan Province, Early 2011
2012, 38(7):848-857.
DOI: 10.7519/j.issn.1000-0526.2012.07.011
Abstract:
Based on various conventional observations, the NCEP reanalysis data, a large scale blizzard process in Hunan Province during 17-20 January. 2011 was analyzed and the process was simulated on dynamic, water vapor, thermodynamic conditions, and cloud microphysical characteristics by the WRF numerical model. The purpose was attempted to discuss the phase transformation of precipitation and the causes for the formation and development of this snowstorm process. The results indicate that, the cold air coming from Ural Mountains and the warm wet air flows coming from the Bay of Bengal and the South China Sea, were meeting with in Hunan for a long time and causing frontogenesis forcing, then strong upward motion was made in the stationary front area. Therefore, the sustained snowstorms took place in Hunan area. Meanwhile, strong upward movement and continuing moisture convergence provided water and power conditions for the snowstorm process, the warm and wet airflow was keeping on the cold air for long time, which provides significant thermal conditions for the long duration snowstorm. Good simulations of snowstorm areas and amount were achieved by model WRF. The formation and development of snow particle were connecting with not only liquid water content, but also the content of ice particle. The main physical process of this snowstorm was probably the deposition growth of snow, the automatic transformation from ice crystal to snow and the collision between rain and snow. The bigger value center of ice snow particulate and the strong upward movement area have indicative significance for the forecast of heavy snowfall.
Based on various conventional observations, the NCEP reanalysis data, a large scale blizzard process in Hunan Province during 17-20 January. 2011 was analyzed and the process was simulated on dynamic, water vapor, thermodynamic conditions, and cloud microphysical characteristics by the WRF numerical model. The purpose was attempted to discuss the phase transformation of precipitation and the causes for the formation and development of this snowstorm process. The results indicate that, the cold air coming from Ural Mountains and the warm wet air flows coming from the Bay of Bengal and the South China Sea, were meeting with in Hunan for a long time and causing frontogenesis forcing, then strong upward motion was made in the stationary front area. Therefore, the sustained snowstorms took place in Hunan area. Meanwhile, strong upward movement and continuing moisture convergence provided water and power conditions for the snowstorm process, the warm and wet airflow was keeping on the cold air for long time, which provides significant thermal conditions for the long duration snowstorm. Good simulations of snowstorm areas and amount were achieved by model WRF. The formation and development of snow particle were connecting with not only liquid water content, but also the content of ice particle. The main physical process of this snowstorm was probably the deposition growth of snow, the automatic transformation from ice crystal to snow and the collision between rain and snow. The bigger value center of ice snow particulate and the strong upward movement area have indicative significance for the forecast of heavy snowfall.
2012, 38(7):858-867.
DOI: 10.7519/j.issn.1000-0526.2012.07.012
Abstract:
Atypical snowfall forecast is a complicated issure in Beijing area. It is especially difficult to determine the role played by the east wind in light snow process. Based on the conventional observation data and various intensive sounding data，two cases including a false snowfall prediction and a first snowfall process occurring in winter 2010 are analyzed. The analysis shows that: Wet or dry conditions for the east wind, depend mainly on the humidity of the upstream eastern region. When the upstream eastern region is dry, the east wind is dry, and thus could not provide moisture for Beijing. The cause for the false snowfall prediction is that the east wind is a dry advection which is unfavorable to humidification at night on December 12, 2010. Low humidity in the boundary layer is the main reason in spite of favorable vertical upward motion. The dry and cold airs in areas north of Beijing moving southwards rapidly and invading are the other major reason for the forecast deviation. Under the favorable condition of abundant water vapor in the boundary layer and weak convergence and ascending motion， a steady rainfall process occurred. The results show that moisture conditions in the boundary layer are very important for winter snowfall prediction. It is difficult to cause effective precipitation even with strong ascending motion in upper air but poor water vapor condition in the boundary layer. In fact， distinct precipitation may occur in case of warm and wet air mass and weak convergence and ascending motion in the boundary layer even without apparent convergence systems.
Atypical snowfall forecast is a complicated issure in Beijing area. It is especially difficult to determine the role played by the east wind in light snow process. Based on the conventional observation data and various intensive sounding data，two cases including a false snowfall prediction and a first snowfall process occurring in winter 2010 are analyzed. The analysis shows that: Wet or dry conditions for the east wind, depend mainly on the humidity of the upstream eastern region. When the upstream eastern region is dry, the east wind is dry, and thus could not provide moisture for Beijing. The cause for the false snowfall prediction is that the east wind is a dry advection which is unfavorable to humidification at night on December 12, 2010. Low humidity in the boundary layer is the main reason in spite of favorable vertical upward motion. The dry and cold airs in areas north of Beijing moving southwards rapidly and invading are the other major reason for the forecast deviation. Under the favorable condition of abundant water vapor in the boundary layer and weak convergence and ascending motion， a steady rainfall process occurred. The results show that moisture conditions in the boundary layer are very important for winter snowfall prediction. It is difficult to cause effective precipitation even with strong ascending motion in upper air but poor water vapor condition in the boundary layer. In fact， distinct precipitation may occur in case of warm and wet air mass and weak convergence and ascending motion in the boundary layer even without apparent convergence systems.
2012, 38(7):868-876.
DOI: 10.7519/j.issn.1000-0526.2012.07.013
Abstract:
By using conventional weather chart data, sounding data, densified automatic weather station (AWS) data, ground based GPS/MET remote sensing observation data of atmospheric water vapor, satellite cloud images, Doppler radar observations and the NCEP/NCAR 1°×1° reanalysis data, the water vapor, thermal and dynamic conditions and the mesoscale characteristics of two snow storms in Shandong Province during 11 to 12 November in 2009 and 28 February in 2010 were comparatively analyzed by using diagnostic methods. The results have shown: (1) The two snowstorms were caused by upper level trough. There were warm and weter advection transported by stronger southwesterly flow at about 700 hPa. All atmospheric levels were near saturated. There were inversion temperatures in the middle low level. The all level temperatures were less than 0℃. The snowstorm occurred in the front of southwest airflow in the 700-500 hPa trough and the converged region of the northeasterly and southeasterly at 850 hPa. Northeasterly winds were prevailing in the surface layer. (2) There were different characters in the two snowstorms. In the November 2009 snowstorm, there was the cold air influenced firstly then the warm and wet airflows run into middle high levels, thus lower energy was stored in low levels, forming a stable heavy snow with longer duration. But in the February 2010 snowstorm, the warm and wet airflows inflowed firstly, then the cold air run into low levels. The vortex formed in low levels and cyclone came into being in the surface.There was convective instability in middle low levels so that convection developed, a snowstorm with great snowfall intensity and short duration occurred. (3) In two snowstorms, the GPS/ MET precipitable water vapor were observations all about 20 mm, which can be an indicator for snowfall amount. The 0℃ isolines of the temperatures observed by densified AWS were the boundary between rains and snows, which can help distinguish the precipitation forms.
By using conventional weather chart data, sounding data, densified automatic weather station (AWS) data, ground based GPS/MET remote sensing observation data of atmospheric water vapor, satellite cloud images, Doppler radar observations and the NCEP/NCAR 1°×1° reanalysis data, the water vapor, thermal and dynamic conditions and the mesoscale characteristics of two snow storms in Shandong Province during 11 to 12 November in 2009 and 28 February in 2010 were comparatively analyzed by using diagnostic methods. The results have shown: (1) The two snowstorms were caused by upper level trough. There were warm and weter advection transported by stronger southwesterly flow at about 700 hPa. All atmospheric levels were near saturated. There were inversion temperatures in the middle low level. The all level temperatures were less than 0℃. The snowstorm occurred in the front of southwest airflow in the 700-500 hPa trough and the converged region of the northeasterly and southeasterly at 850 hPa. Northeasterly winds were prevailing in the surface layer. (2) There were different characters in the two snowstorms. In the November 2009 snowstorm, there was the cold air influenced firstly then the warm and wet airflows run into middle high levels, thus lower energy was stored in low levels, forming a stable heavy snow with longer duration. But in the February 2010 snowstorm, the warm and wet airflows inflowed firstly, then the cold air run into low levels. The vortex formed in low levels and cyclone came into being in the surface.There was convective instability in middle low levels so that convection developed, a snowstorm with great snowfall intensity and short duration occurred. (3) In two snowstorms, the GPS/ MET precipitable water vapor were observations all about 20 mm, which can be an indicator for snowfall amount. The 0℃ isolines of the temperatures observed by densified AWS were the boundary between rains and snows, which can help distinguish the precipitation forms.
2012, 38(7):877-883.
DOI: 10.7519/j.issn.1000-0526.2012.07.014
Abstract:
Using basic observational data and NCEP reanalysis data, a disastrous snowstorm weather of missing report in the northeast of Inner Mongolia was analyzed diagnostically. The results showed that this snowstorm weather process is different from the conceptual model in synoptic meteorology of snowstorm in Inner Mongolia. There is no powerful water vapour transport, the large value area of vertical ascending motion is concentrated between 850 hPa to 500 hPa, and the heavy snow has the mesoscale characters of short duration, great intensity, small range and serious disasters. In this process, the powerful warm advection of 850 hPa is cooperated with the weak and cold advection in the southwest airflow of 500 hPa, the temperature advection in the lower troposphere decreases with altitude which is of benefit to the construction of unstable stratification, the mergence and reinforcement of ground secondary cold front with cyclone and the intensive development of mesoscale low vortex of 850 hPa strengthen convergence ascending motion in the lower troposphere, and unstable energy release is the main cause of snowstorm. Finally, the “cold wedge” of boundary has some amplification effect on heavy snow.
Using basic observational data and NCEP reanalysis data, a disastrous snowstorm weather of missing report in the northeast of Inner Mongolia was analyzed diagnostically. The results showed that this snowstorm weather process is different from the conceptual model in synoptic meteorology of snowstorm in Inner Mongolia. There is no powerful water vapour transport, the large value area of vertical ascending motion is concentrated between 850 hPa to 500 hPa, and the heavy snow has the mesoscale characters of short duration, great intensity, small range and serious disasters. In this process, the powerful warm advection of 850 hPa is cooperated with the weak and cold advection in the southwest airflow of 500 hPa, the temperature advection in the lower troposphere decreases with altitude which is of benefit to the construction of unstable stratification, the mergence and reinforcement of ground secondary cold front with cyclone and the intensive development of mesoscale low vortex of 850 hPa strengthen convergence ascending motion in the lower troposphere, and unstable energy release is the main cause of snowstorm. Finally, the “cold wedge” of boundary has some amplification effect on heavy snow.
2012, 38(7):884-889.
DOI: 10.7519/j.issn.1000-0526.2012.07.015
Abstract:
During the winter (December 2011-February 2012), the surface air temperatures were below normal in most China, and the mean temperature in China was -4.8℃, being the coldest winter since 1986. The extreme low temperature climate events were prevailed in China such as the extremes of daily temperature drop (DTD), which were observed in Inner Mongolia, Xinjiang, Xizang and Shaanxi. The possible cause for the extreme low temperatures in China was investigated by using the conventional observational temperatures and NCEP reanalysis datasets. The results have shown that the strong East Asian winter monsoon might be responsible for occurrence of extreme low temperatures, with dominating of anomalous cold high pressure system over the Siberian Plain, persistence of blocking system over the Ural Mountains and Baikal Lake, and deeper than normal East Asian major trough. Further analysis shows that La Nina might cause the abnormally stronger East Asian winter monsoon.
During the winter (December 2011-February 2012), the surface air temperatures were below normal in most China, and the mean temperature in China was -4.8℃, being the coldest winter since 1986. The extreme low temperature climate events were prevailed in China such as the extremes of daily temperature drop (DTD), which were observed in Inner Mongolia, Xinjiang, Xizang and Shaanxi. The possible cause for the extreme low temperatures in China was investigated by using the conventional observational temperatures and NCEP reanalysis datasets. The results have shown that the strong East Asian winter monsoon might be responsible for occurrence of extreme low temperatures, with dominating of anomalous cold high pressure system over the Siberian Plain, persistence of blocking system over the Ural Mountains and Baikal Lake, and deeper than normal East Asian major trough. Further analysis shows that La Nina might cause the abnormally stronger East Asian winter monsoon.
2012, 38(7):890-896.
DOI: 10.7519/j.issn.1000-0526.2012.07.016
Abstract:
The characteristics of general circulation of atmosphere in April 2012 are as follows. There is only one polar vortex center in the Northern Hemisphere, and the strength is similar to normal years. There are four waves around the earth in middle high latitudes and the strength of Ural blocking high is higher than the normal that leads to several streams of cold air to influence China. More south waves are at middle low latitudes and the East Asia major trough is stronger than usual at the same period. In April, the mean temperature is 11.7℃, 1.0℃ warmer than the same month of normal years (10.7℃). The average precipitation over China is 45.6 mm which is 2.5 mm more than climatological normal 43.1 mm. There are 8 rainstorm precipitation events and 6 sand dust events in April. Especially in South China and Jiangnan area many severe convection events with thunderstorm gale and hail happening.
The characteristics of general circulation of atmosphere in April 2012 are as follows. There is only one polar vortex center in the Northern Hemisphere, and the strength is similar to normal years. There are four waves around the earth in middle high latitudes and the strength of Ural blocking high is higher than the normal that leads to several streams of cold air to influence China. More south waves are at middle low latitudes and the East Asia major trough is stronger than usual at the same period. In April, the mean temperature is 11.7℃, 1.0℃ warmer than the same month of normal years (10.7℃). The average precipitation over China is 45.6 mm which is 2.5 mm more than climatological normal 43.1 mm. There are 8 rainstorm precipitation events and 6 sand dust events in April. Especially in South China and Jiangnan area many severe convection events with thunderstorm gale and hail happening.
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ISSN:1000-0526 CN:11-2282/P