Abstract:To promote the process of weather forecasting to be more professional and accurate, the potential forecast for predicting severe weather area has been conducted by Severe Weather Prediction Center in NMC since 2009. Realtime products for monitoring strong convective weather based on severe weather report from automatic weather stations, observations from national lightning monitoring network, FYseries satellite and radar networking etc. have been put in use. Criterion for mesoscale weather analysis has been established in MICAPS V3.0 system. The diagnostic products of mesoscale convective system outputted by the application of T639 global model， GRAPESRUC model and WRFEPS model have been developed. Guiding products for predicting classified severe weather (thunderstorm, hail and gale) area have also been issued. Prediction qualities were examined and assessed from April to September in 2009. The results show that the 6hourinterval TS scores of thunderstorm， local torrential rain， and hail and gale are 18%, 2.6%, and 2.1% separately, while 12hourinterval TS scores for each are 18.4%, 4.1% and 1.3%, respectively.

Abstract:Ten heavy rainfall processes，which caused severe flooding in Jilin and Liaoning Provinces of Northeast China, occurred during July to August in 2010. The total precipitation is characterized by frequent processes, large amount precipitation and colocated rainfall area. By using the observational data of surface, upperair, satellite, Doppler radar, regional AWS and the operational NWP analysis data of T639 and NCEP FNL, the causes for the above characteristics are presented. The main results are as follows: (1) The frequent rainfall processes are mainly caused by the convergence of westerly cold air flow and strong warm, moist southerly air flow, which are supported by a stable and abnormal general circulation. (2) The ten rainfall processes can be divided into two categories based on the most important upperair influence weather system, category one is about low vortex (including shear line) mainly occurring at low levels, category two is about cold vortex (including trough) mainly occurring at middle to higher levels. The circulation characteristics, water vapor source and the role of cold air are different for each category. (3) Case study of each category shows that the large amount precipitation is caused by the convective cells, which initiated at almost the same place and moved through the concerned place frequently. (4) The mechanism of cells initiated is different for two cases. The case “7.20” convective cells are initiated at the ascent and potential unstable zone of geostrophic deviation wind convergence and ahead of cold front aloft; the case “7.27” convective cells are mainly triggered by surface front. (5)The Corfidi vector method provided a good estimate of the motion of the most active elements of the convection system. The above results are valuble to heavy rainfall forecasting of the Northeast China. The analysis method can be also applied to the heavy rain forecasting of other places.

Abstract:Based on conventional observation data, satellite data, automatic weather station data and NCEP(1°×1°) reanalysis data, the physical mechanisms and mesoscale features of severe convective weather processes in Anhui Province in recent ten years （2001-2010） are analyzed. The results show that: The development of severe convective weather is related to the largescale circulation background, which needs abundant water vapor, unstable stratification, the trigger mechanism or strong lifting, and the strong development of strong storms often have inversion layer, strong vertical wind shear, midlevel dry air and other favorable conditions. However, the importance of these conditions in different largescale circulation backgrounds is not the same, and these conditions also produce different types of severe convective weather. The convective instability of cold vortex pattern and behind trough shows that: the lapse rate of temperature in lowlevels is large; vertical wind shear is strong; the wind strongly clockwise with height increasing; westerly jet exists in 400-500 hPa, which is closely related with the severe weather area; and there exist obvious mesoscale low pressure, convergence line, and dry line. This pattern mainly causes thunderstorm, strong wind and hail. The CAPE is usually large in ahead of trough pattern, lowlevel jet exists, the horizontal and vertical shears of wind are large; the shortwave trough moving to east rapidly is the main trigger mechanism of strong convective weather; and the lowlevel moisture condition is good. This pattern mainly causes thunderstorm, strong wind, flood and tornado. Through statistics of the various weather elements and physical parameters of severe convective weather under different types of largescale circulation background, and extraction of eliminating empty forecast indicators using environment field, we will significantly improve the tornado identification ability and earlywarning level based on the reflectivity factor and the average radial velocity of Doppler radar. This paper compares the physical mechanism and mesoscale characteristic differences between two severe convective weather processes which caused squall line, vast thunderstorm wind and hail on HuangHuai and JiangHuai Regions one of which occurred in the situation of subtropical high edge and ahead of trough during 19-20 July 2010, the other occurred in the situation of Northeast cold vortex on 3, 5, and 14 June 2009. This work may improve shorttime forecasting ability of severe convective weather under different types of largescale circulation background.

Abstract:A particularly challenging event occurred on 22 July 2009 in Beijing area. The convective storm moving from the mountain to the plain suddenly intensified as it approached the foothills, and then intensified again as it moved onto the plains. Based on the fourdimensional Variational Doppler Radar Analysis System (VDRAS), this paper presented a deep investigation focusing on the intensifying mechanism of the convective storm under weak synopticscale forcing over Beijing area using Doppler radar, wind profile, surface observation, 4 times daily radiosonde and NCEP data. Results have shown that: The weak cold front triggered the convective storm. The thermodynamic unstable condition including warm, humid, lowlevel southerly wind and significant accumulation of the convective available potential energy (CAPE) indicated by the sounding over plain, and the significant dynamic instability with strong lowlevel vertical wind shear indicated by the wind profiler provided the favorable local environment for the intensification of the storm. In the first intensification stage, the terrain forcing played a dominant role, including: (1) acceleration of cold pool outflow whose kinetic energy drived from potential energy, leading to strong down flow and strong convergence; (2) uplift of south warm moist air flow at the south of piedmont, resulting in a strong upward motion; (3) lifting of the thunderstorm cold pool outflow, which formed strong lowlevel vertical wind shear between north outflow at the low level and south air flow on the surface and led to cold advection over the warm and moist southerly flow, thus enhanced both the dynamic and thermodynamic instability in front of the storm. The second intensification of the thunderstorm in the eastern urban area, was mainly caused by the presence of the strong perturbation temperature gradient zone in the boundary layer in Chaoyang District, resulting from the confrontation of the cold pool outflows of the wellorganized thunderstorm and the lowlevel warm tongue, and the balance between positive and negative vorticities. The intense updrafts pushed by the interactions between the cold outflow and the warm moist southerly flow, coexisted with the downdraft at the rear of the thunderstorm for a long time. The negative vorticity due to the vertical inhomogeneity of the outflow, was balanced with the positive vorticity due to the vertical inhomogeneity of the environmental flow. According to the RKW theory, this equilibrium state was very favorable for the formation of vertical updraft so that maintained the storm and led to the second intensification.

Abstract:A squall line with two different gust fronts occurred in central Liaoning in August 2009, accompanied by strong convective weather phenomena such as disastrous wind and hail. The developing processes of the two gust fronts were analyzed based on Doppler radar data, radiosonde data, surface meteorological observation data and Aircraft Meteorological Data Acquisition and Relay (AMDAR) data. The results indicate that the strong vertical wind shear in background field intensified the growth of convective cells in the squall line and made its inclining. The westerly cold flow, entering the back of squall line, stimulated the convective activities of the cells and gave birth to the first gust front. The acceleration of westerly surface flow, produced by the great temperature gradient of a northerly cold flow and the warm core of the squall line is the instant cause for the genesis of the second gust front. The lineshaped convergence zone was formed in the major body of the squall line moved to the second gust front， which became a new squall line finally.

Abstract:By using conventional meteorological observations, real time operational numerical forecast models, ECMWF ERA Interim global reanalysis data (1.5°×1.5°) and NCEP global reanalysis data (1°×1°), a preliminary analysis is made about the reason that Super Typhoon Megi (1013) abruptly northward recurvated after it moved into the South China Sea. And three subjective forecasts of CMA, JMA and JTWC and some operational numerical model forecasts for Megi’s abruptly northward recurvature are verified and estimated. The results show that the main reason that Megi’s abruptly northward recurvature in the South China Sea is the mergence of the equatorial buffer zone and the subtropical high ridge located at the east side of Megi while the Southern Hemispheric crossequatorial flow northward poured. The analysis also shows that the multimodel consensus forecast or the super ensemble prediction of tropical cyclone track is an effective way to solve their uncertainty when operational numerical forecast models show large differences for the track of a tropical cyclone. Therefore it is necessary to strengthen the development of integrated application platform about multimodel consensus forecast or superensemble forecast for tropical cyclone track. Then it is essential to further improve the existing operational tropical cyclone forecast work flows on the basis of the platform development.

Abstract:By using conventional meteorological observation data, NCEP reanalysis data, satellite and radar data, densified surface observational data, etc., a rare rainstorm process which happened during June 17-20, 2010 in northern Jiangxi was analyzed. In this paper, the heavy rain process was analyzed from three aspects: dynamics and diagnosis analysis, mesoscale analysis, and simulation analysis by WRF model. The analysis results show that: (1) This rare rainstorm is a typical heavy rain over Meiyu front, it is caused by the vigorous development of strong mesoβ system generated in the extremely favorable weather situations. The cold air flow behind the 500 hPa East Asia trough joined up the SW flow located in the northwest part of the strong and stable subtropical high, thus the cold air and warm air converged and maintained over the northern part of Jiangnan.(2) Since the area that cold air and warm air joined up is stable and the SW warm and wet flow is abnormal strong, the vapor, dynamical, and thermodynamic conditions leading to heavy rain are quite adequate, the physical quantities are significantly higher, these are very helpful to trigger the strongly development of meso and microscale convection systems.(3) The extraordinary rainstorm is caused by the interaction of many factors such as strong vapor and convergence ascending motion, weak cold air activities in middlelevels, the strengthening of SW lowlevel jet, the weakening of stablility of convection layer, stability of surface convergence lines, the formation and maintenance of mesoβ vortexes and strong divergence in higherlevels, etc.(4) Numerical simulation analysis of WRF model shows that at 08:00 BT 19 June 2010, the formation of mesoβ vortex is related to the strengthening of weak cold air and warm and wet flow, the vertical thickness of this vortex is between 950 and 550 hPa, and it is the strongest between 800 and 950 hPa. In addition, a string of intense convective systems appear in the southern part of this mesoβ vortex, these systems are nearly in eastwest direction and the scales are about 30 to 60 km, and their positions are well corresponding to the severe rain area.

Abstract:The routine observational data, the NCEP 1°×1° 6 h analyzed data and Doppler radar information were used in comparing two heavy rain processes under the posttrough on 7 May and the priortrough at 500 hPa on 14 May 2010 in Guangzhou.The results show that the 7 May torrential rain was caused by the shear line at 850 hPa and the northwesterly air flow after the trough at 500 hPa, which increased stratification unstability when it moved over the warm and wet air mass at low levels, this differs from the traditional circulation during the presummer flood season in South China. The “14 May” torreitial rain happenned under the influences of the southwesterly air flow before the trough at 500 hPa, the shear line at 850 hPa and the coldair injection on the ground surface. The squall line affected these two processes, in which the former had longer squll line, the larger area of the strong echo in squll line, more super cells and stronger rain intensity and higher total precipitation. The mechanisms of maintaining and development of the squall line in two processes were different in that, the former relied on the supplement and merging the new cell from the border of Guangdong and Guangxi, and the latter depended on absorbing and merging the new cell ahead of it or along the convergence zone on the ground surface.

Abstract:The heavy rainstorm resulting from depression circulation of typhoon Meranti is studied with the analysis of Doppler radar reflectivity, mesoscale observational data and the diagnosis of the simulation results from the mesoscale numerical weather research and forecasting model (WRF). The main results show that the remained cloud system of Meranti, the warm and moist flows in the border of subtropical high and the weaker cold air from higher altitudes are responsible for this rainstorm. The precipitation radar reflectivity consists of cumulus and stratus, which can produce more precipitation amounts than a unique kind cloud. The interaction among several meso and microscale convective systems is advantageous to the development of local convective cloud cluster, and the wind velocity zone occurs with the enhancement in the intensity and area of wind velocity. During the period of rainfall, the moist condition for precipitation is satisfied with the moist transporting into the rainfall region. The configuration of the vertical helicity at mid and low levels, the strong ascending movement resulting from the invasion of the weak cold air into the air column where the negative moist potential vorticity is at low levels and the positive moist potential vorticity is at middle and upper levels, and the heating effect coming from the latent heat release made a sustained pumping action, which leads to the standing raining and forms the rainstorm in Hangzhou. This can be an index for forecasting tropical cyclone local rainstorm.

Abstract:Based on the observed data and output data from MM5, the terrain effect on the blizzard process in central and south of Hebei Province from November 10 to 11 in 2009 is analyzed. The results show that there is a downward motion on the north side of the trumpetshaped terrain, and an upward motion on the south side; the eastward flow has been brought together due to the role of the trumpetshaped terrain, the terrain effect exists under the 800 hPa and an upward motion is generated. Vertical profiles show that the lowlevel upward motion generated by terrain penetrates through the inversion layer, and merged with upward streams caused by westerly trough, thus strengthening the vertical upward movement. The northeast flow encountered Taihang Mountains is divided into two flows, a flow sinking in the piedmont, and the other flow ascending before the cold air heap and gradually forms a piedmont circulation of cold air sinking branch, indicating accumulation of cold air in the piedmont. This may be the main reason for snowfall center occurring generally in the plains and not in the hill.

Abstract:In this paper, the synoptic background, the nongeostropic 〖WTHX〗Q〖WTBZ〗vector contribution and the phase change of the conditions are analyzed in the process of heavy snowstorm and heavy rain in Northeast China during March 3-6, 2007. The results have shown that: a wide range and strong southerly jet is not only a strong water vapor belt, but also the necessary conditions for the lower front and lowlevel system to strengthen and move; the forcing of secondary circulation in the torrential rain plays an important role in the occurrence and development of process, its strength is directly related with the rainfall intensity. The level of cloud systems and whereabouts in the process of stratification state of the lower front to a certain extent determine the phase state of precipitation on the ground. Deep strong front zone, JiangHuai cyclones, lowlevel jet, and the intensity of nongeostrophic 〖WTHX〗Q〖WTBZ〗 vector are closely related with the location of precipitation band and its intensity.

Abstract:The causes for the 6 May 2010 severe windstorm were analyzed in Chongqing by using conventional observations, NCEP analysis fields, radar and AWS (automatic weather station) data, etc. The results showed that the almost overlapping configuration structure of the cold front and the subtropical upper jet promoted the formation of secondary circulation with contributing to the development of strong upward motion near the windstorm area. It was significant that the atmospheric convective instability was strengthened by the underlying surface strong heating, the low temperature and humidity increasing and the drycold air in the middlehigh level in the day before the storm, which made for the formation of thunderstorm. The strong index gradient areas at the edge of the CAPE, K, SI highvalue area and the CIN smallvalue regions were significant indicators to forecast the strong wind and hail. The radar echo was characterized by threebody scattering, weak echo area, and hail echo. The midlevel radial convergence and the reflectivity core up and down repeatedly were also the important features of the surface gale and hail formation. The northeastsouthwest oriented mountain range blocked the cold air moving direction in eastern Sichuan Basin. The troughshaped terrain provided a larger space for the sustained development of multicell storm between the mountains. The south terrain of Mingyue Mountain played a role of uplifting and triggering. The narrow tube effect of terrain blocking enhanced the formation of downburst leading to the surface high wind, which was the important reason for the formation of 11 rank gales.

Abstract:Using NCEP (1°×1°) 6 h reanalysis data, observational data and new generation Cband Doppler radar data, a strong thunderstorm process in Keping, Aksu in August 19, 2009 was investigated. The results show that the mesoβ shear line, the surface mesoscale low and the convergence line are the direct affecting systems of thunderstorm. The water vapor came from the eastern and middle regions of Tarim Basin, and the water vapor transportation was concentrated at low levels, where the easterly jet stream took a vital part in the water vapor transportation. Convective available potential energy had increased before the thunderstorm occurred. The thunderstorm developed initially from an ordinary rainstorm, then evolved gradually into a hailstorm, and lasted more than an hour. The reflectivity of the hailstorm at its mature stage displayed a middlelevel echo overhang aloft and weakecho region.

Abstract:Intensity changes of convective cells in the Hangzhou Bay observed by Zhoushan radar from January 2007 to June 2010 when entering the sea are studied, and they depend on the combined reflectivity factor, ET, VIL, radial velocity, hail index and so on. The results show that the possibility of convective cell strengthening or its maintenance nearby the coastline is quite big. Meantime, the possibility of convective cell strengthening nearby the north coastline is big, while the possibility of convective cell weakening nearby the south coastline is also big. The possibility of convective cell strengthening or maintaining from evening to dawn is still big. The temperature and humidity characteristics in the coastline， the surface wind convergence， and atmospheric stability are analyzed from three typical cases. And the mean values of the temperature, relative humidity gradients and horizontal wind shears in the Hangzhou Bay concerning various cell changes are calculated. The result shows that the three factors above of the strengthening cells are bigger than the weakening cells. In conclusion, the above three conditions should be considered when judging a convective cell in the Hangzhou Bay is strengthening or weakening.

Abstract:The gale process which happened in Laizhou Gulf on April 27, 2010 was analyzed diagnostically by using the NCEP data. This study shows that the explosive extratropical cyclone strengthened the frontogenesis behind the cyclonic cold front, thus increased the pressure tendency gradient which was the main reason for this gale process. By analyzing the synopsis environmental field, the temperature advection, the vorticity advection, the high level jet stream and the anomaly of the high level potential vorticity diagnostically, it is concluded that the strong barocline and the accompanied cold and warm advections made the high level trough develop. In the initial stage the vorticity advection difference between the high and low levels played an important role in the surface extratropical cyclone development. Then the cyclone developed further because of the divergence caused by the ageostrophic components to the left of the jet stream in front of the trough. The downward propagation of the potential vorticity on top of the troposphere triggered the surface cyclonic current and thus the cyclone developed explosively.

Abstract:The following are the main characteristics of the general circulation of atmosphere in April 2011. There is one single center of the Northern Hemisphere polar vortex and is located in the Western Hemisphere. There are three waves around the earth in middlehigh latitudes and is one wave in Asia area. The East Asia deep trough is stronger, the subtropical high is obviously weaker than climatological normals and the south branch trough is approaching the climatological normals. The monthly mean temperature averaged over China is 11.3℃ which is 1.0℃ higher than climatological normals and that in Northwest China is obviously higher. The monthly mean precipitation averaged over China is 21.4 mm which is 22.4 mm less than climatological normals. There are four cold air currents and four sanddust processes in April respectively. Some provinces and regions are hit by severe convective storms.