Studies On Climatic Characteristic Of Rainstorm And A Typical Rainstorm Case In Hunan

In order to understanding the Hunan rainstorm temporal and spatial distribution, climatic characteristics of heavy rainfall and the development of the rainstorm forecast,summing up successful experience, it can improve the rainstorm prediction technique level, preventting flood disasters, and provide scientific basis. The article used the precipitation datas of1980-2009years to analyze Hunan rainstorm’s smporal distribution. The change of rainstorm period cycle was diagnosised the trend of distribution by using the wavelet transformation. By using M-K nonparametric test, the article reserched trend analysis and mutation test of the storm flood time seties, analyzed the trpical atmospheric circulation characteristics of rainstorm in Hunan. The article researched on the typical rainstorm process on June19,2010. Using of Changsha Doppler radar datas, diagnosising the rainstorm process throughout the Hunan area, the results showed that the relations are intensive between mechanism of the rainstorm and the change of enrironmental physical quantilies. Especially in some strong precipitation area, it always appeared lower level positive vorticity、upper-level minus vorticity and strong vertical motion. It was from the study of dynamic physical quantilies that it showed the area of rainstorm consistency coherence and the physical structure, in order to providing the rainstorm occurrence and development basic datas.The main conclusions were:1、The characteristic of the annual rainstorm days was higher in the north and lower in the south; and daily maximum precipitation was higher in north and south, but lower in central and southwestern; rainfall mainly concentrated in the5-8months; the total number of rainstorm was in June,2283times, and heavy rainfall in July,402times.2、There were period changes of the annual rainstorm days and daily maximum precipitation. In1980-2009years, the period changes of the annual rainstorm days’number in Hunan was divided into2periods. Before2000years the rainstorm day number had2characteristic time scales, respectively,7years and20years. After2000years the rainstorm day number had2characteristic time scales, respectively,3years and20years. The periodic change of daily maximum precipitation had3characteristic time scales, respectively,4years,7years and20years. Using Mann-Kendal (M-K) non parameter method to testing trend analysis and mutation test of annual precipitation, UF indicated that after1992the annual precipitation in Hunan was increasing. According to UF and UB intersection point position determined the increasing precipitation early1990s was the mutation phenomenon.3、Effecting of rainstorm in Hunan circulation situation can be divided into double obstruction, single obstruction, latitudinal type. In addition, concentrated rainfall areas affected by tropical cyclone landfall weakened low pressure situation.4、It was from the study of radar datas that main reason primary cause of regional heavy rain are the maintaining convective-stratiform mixed clouds and generating and developing convection cell. The contribution of low level jet to torrential rain process was significantly. There were AWR areas in radar radial velocity maps and convergence lines in low layer. It was from the study of wind profile that there were cold air instrusion and vertical wind shear in high level, warm advection in low layer.5、Through testing rainstorm on June19,2010,in Hunan and, diagnosising the correlations physics, it showed:in time of the strong precipitation, precipitation area general corresponded to vortex positive vorticity region, and in the positive vorticity zone the south airflow easily occursd rainstorm. From the storm forming dynamic conditions, vorticity, divergence and vertical vorticity configuration formed the the mechanism of positive feedback in the storm period. The lower level positive vorticity and upper-level minus vorticity improved water vapor upward motion, and that played an important role in the strong precipitation maintenance. The southerly warming and wetting flow with northerly cold air southward invasion, cold and warm air radiolysis merged to produce a cyclonic circulation. That was beneficial to the development and maintenance of torrential rain.6、In the torrential rainstorm on June19,2010, in Hunan, there were very strong vapor transportation and convergence in rain belt.The water vapor convergence of north and south is beneficial to the increase of storm rainfall. Vapor transport and convergence area southwards as well as the intensity change played a very good instruction. From analyzing hight and low altitude jet stream, the heavy rain area happended in the right side of the entry domain of the hight jet stream and the left side of the entry domain of the low jet stream. The secondary circulation ascending branch linked to low jet stream located in the left side of the low-level jet stream. That was conducive to the occurrence of the strong convection and heavy rain. Low level jet stream bringed a large number of the warming and wetting air. Forming positive water vapor advection in rainfall area played an important role on establishing and maintaining the rainstorm area low convective unstable stratification and prompting in favor of rainstorm weather condition to form.7、The wet potential vorticity reflected that the convective instability of atmosphere instability contacted with the baroclinic instability. The MPV barotropic and baroclinic reflected convection instability, symmetry instability and baroclinic instability of the atmosphere. Rainstorm occurred in850hPa MPV barotropic negative near the center and wet baroclinic vorticity item in region. The middle-lower troposphere MPV1<0, MPV2>0configuration indicated the rainfall area.