| Jilin is located at the center of Jilin Province,which is temperate continental climate,and the meteorological disasters occur frequently.In Jilin,raining is frequent in summer,especially for rainstorm and rain shower,and the short-time heavy rainfall usually causes floods and droughts.Therefore,rainstorm is one of the major weather disasters in Jilin.In practice,the forecast of rainstorm is the key point and also a challenge of meteorological work.Therefore,it is necessary to strengthen the research and analysis of the climate feature and influencing system of the rainstorm,and then explore the mechanism of rainstorm and forecasting method.The main influencing system of Rainstorm in Jilin city are as follows:(1)the subtropical high rear shear rainstorm,which mainly occured in June-August;(2)the northeast cold vortex rainstorm,which mainly occured in late June to mid August;(3)the rainstorm impacted by typhoon;(4)the rainstorm impacted by cyclone(including Mongolia cyclone,North China cyclone and Jianghuai cyclone);After analyzing the climatic features of rainstorm in Jilin city,we found the variation trend,the spatial distribution characteristics,the main influencing system and the circulation characteristics of rainstorm.If the subtropical high is strong in July,the frequency of rainstorm would increase within this year.The results show that there are two main types of rainstorm circulation: the first type is typhoon northward;the other type is the interaction between subtropical high northward extension and westerlies which bring large amounts of cold air.The mechanisms of these two types of rainstorm are different.The first type of rainstorm is mainly due to the interaction between the warm-wet air from the subtropical high and the cold air from the westerlies;the second type of rainstorm is mainly caused by two mechanisms: first,the interaction between typhoon and westerlies;Second,the terrain effect of Changbai Mountain.After the analyzing of the climatic characteristics of rainstorms in Jilin,the results show that: there are three years which occur rainstorm two times within a year,they are 1980,1986 and 1994,separately.There are sixteen years have no rainstorm,which account for the 1/3 in the totality.Interannual variability of rainstorm is not significant,the probability of the occurrence of rainstorm in Jilin is not high,the rain storms mainly occur in June-August.The distribution of rainstorm in the year is unimodal.The rainstorm occurred most frequently in the late July,accounting for about 24%,followed by the esrly August,accounting for about 20%.The spatial distribution of rainstorms in Jilin is: the rainstorm frequency in northwest of Yongji and south of Panshi and Huadian are more than those in Jiaohe and Shulan.According to the characteristics of the physical quantity field of rainstorm,the rainstorm circulation,water vapor supplies and dynamic conditions,it is possible to establish the rainstorm weather forecasting method and also important for the prediction of strong precipitation weather.The features of cyclone rainstorm are that it located at the left of low-level jet and the right of mid-level and high-level jet.The features of subtropical high rear formation rainstorm are that the obvious characteristics of water vapor and divergence flux;the influenceing weather systems have enough dynamics and the water vapor is abundant.The physical characteristics of rainstorm caused by cold vortex are that the energy moves from the higher level to the lower level during the developing period with potential instability;the stable rainfalls mainly occur during mature period.Development of rainstorm mainly relies on the cold air in the lower troposphere from the northwest and the northward transportation of warm-wet air.We found that regional rainstorm process can analysed by water vapor conditions(dew point,specific humidity,moisture flux,flux divergence and 700 hPa relative humidity),dynamic conditions(vertical velocity,divergence and vorticity etc.)and unstable conditions(the K index);the falling area can be determined by the high or low level jet.Therefore,the forecasting can be processed by the analysis of relevant physical quantities of the strong rainfall area and intensity to make preliminary judgment.According to the characteristics of the physical quantity field of rainstorm,the rainstorm circulation,water vapor supplies and dynamic conditions,it is possible to establish the rainstorm weather forecasting method and also important for the prediction of strong precipitation weather. |
