| Based on the conventional surface and aerological observational data, non-conventional various observational data, the data of satellite and Doppler radar and NCEP Reanalysis data, by using method of meteorological analysis, dynamic diagnostics analysis and numerical simulation, has an overall analysis of a regional excessive snowstorm in North China on November 9-12 in 2009. The analysis is as follows:characteristics of circulation situation, features of circulation in North China, TBB characteristics of meso-scale cloud cluster, features of Doppler radar, meso-scale systems in the process of excessive snowstorm.It shows that, the combined action of cold air and warm air contributes to this snowstorm. The cold eddy in the north of Lake Baykal which tend east and south developed while the wedge near Lake Baykal reinforced in high-level of 500 hpa, so the polar cold air was led to south and accumulated in Northeast China. In the meanwhile, cold air in low-level flowed reversed to North China Plane through Pohai, various short-wave troughs divided from the trough near Balkhash lake and turned east. In 700 hpa, short-wave troughs superposing the southern branch trough in the same phase, reinforced the southwest warm and wet air in front of trough. In the surface map, it shows that in North China Plane, the baric field is high in the east and low in the west, inverted trough near the Great Bend of the Huanghe River developed with circumfluence, while southwest warm and wet air met the northern cold air in the high-level of southern Hebei, causing the excessive snowstorm in southern Hebei.This process is in close relation to the dynamic coupling of torrent in high and low level, the snowstorm appeared on the right and back of inlet region of northern branch aerological torrent, the left and front of outlet region of souhern branch aerological torrent, and the left and front of low-level torrent. The low-level southwest torrent transported sufficient vapor and energy for the snowstorm area while the northeast torrent supplied favorable dynamic condition for snowstorm. The vapor of snowstorm is mainly from the south, it was transported to snowstorm area with southwest air in mid and low level. Though the eastern air near boundary layer turned through Pohai, it is quite dry. Anticyclone and divergence area is in surface layer of snowstorm area, in vertical direction, divergence and convergence center superposed the plus and minus vorticity center, strengthened the ascending motion, and transported warm and wet air in mid and low level to high-level, thickening the wet layer above snowstorm area. The powerful cold and warm air met and aroused a meso-scale system, followed by meso-scale convective cloud clusters, three meso-scale convective clusters influenced the southern Hebei. Right in this time, TBB of cloud is below -40 centi-degree and TBB of the strongest center is below -50 centi-degree. The snowstorm appeared in the area combined by mid-level convective instability and baroclinic instability. Conditional symmetrical instability in high-level superposed the convective symmetrical instability in low-level, contributing to the form of snowstorm.The radar echo during snowstorm is precipitation echo mixed by cumulus and stratiform clouds which is the major factor. The reflection index is generally 15-30BZ, with some above 40dBZ; there is warm advection in radial velocity field of radar, urves of zero velocity is unsmooth and the headwind area appeared. There is southwest torrent in high-level and northeast torrent in low-level; the height of echo peak is 5-6km and some is 8km.The windward slope and pipe socket landform in the eastern foot of Taihang Mountain are crucial, both force lifting and maintaining the cold cushion in low-level of snowstorm area, so it is the key factor of circumfluence snowstorm.
|
PDF Full Text Request