The Characteristics Of Typhoon Rainstorm And Terrain Effect In Guangxi

Typhoon is one of the major catastrophic weather systems in China.The strong winds and heavy precipitation brought serious economic losses and casualties to the affected areas.Guangxi's complex terrain caused uneven Spatio-temporal distribution of precipitation,and rainstorms and floods of typhoon frequently occurred.Guang Xi is one of the most frequent occurrences of typhoon storms in China.The paper processed and analyzed meteorological and disaster data through GIS and MICAPS system.Univariate linear regression and correlation analysis were used to analyze the climatic characteristics of typhoons which had direct or indirect impact on Guangxi in the 60 years from 1949 to 2016.Especially,the Western Pacific typhoon and the typhoon in the South China Sea,which have entered the Guangxi influence area in 1987-2016 years,are classified according to the types of landing path and the heavy precipitation processes and landings that have been brought to Guangxi,It showed the climatic characteristics of typhoons entering the Guangxi influence area for the last 30 years.Taking the typical torrential rainstorm process of the super typhoon "Rammasun" as an example,It is researched the formation mechanism of this catastrophic rainstorm by analyzing the general circulation situation,physical quantity fields,satellite and radar data,and particularly discussed the forcing effect of terrain factors on this rainstorm process.In order to verify the effect on the increase of typhoon rainstorm by uplifting the terrain,two experiments of the control and the sensitivity based on WRF model are designed,and do the numerical simulation.Get the following conclusions:(1)In the past 60 years,359 typhoons have entered the affected areas in Guangxi,and about 5 typhoons each year have a direct or indirect impact on Guangxi.The period of high incidence of typhoons affecting Guangxi is happened approximately 20 years.In the past 30 years,70% of the typhoons which have entered Guangxi's impact zone have brought heavy rainstorms to Guangxi.(2)In the past 30 years,there have been 79 typhoons in the northwestern Pacific Ocean that have entered the affected areas of Guangxi,and 70% of typhoons caused rainstorm or torrential rain in Guangxi.Among those typhoons,50% are typhoons on the West Road typhoons,which the torrential rain are mainly distributed in Southwest Guangxi;34% are typhoons on the Middle Road,and most of them can penetrate deeply into Guangxi's interior,The torrential rain areas are mainly distributed in South of Guang Xi,especially Southeast of Guang Xi;Although the number of typhoons on the East Road is not much,but it has the highest probability(83.3%)of generating heavy rainfall.(3)There are 58 typhoons(including Tropical Depressions)in the South China Sea entering the affected areas of Guangxi,and 65% of typhoons can bring rainstorm and rainsorm above to Guangxi.Most of the typhoons in the West Road(78%)can produce rainstorm and rainsorm above in Guangxi.The rainstorm falls mainly in South of Guangxi;the vast majority of the mid-road typhoons(88.9%)will cause rainstorm and rainsorm above in Guangxi.The rainstorm falls mainly in the East of Guang Xi;the number of typhoons on the East Road is not much,and there is basically no obvious precipitation impactng Guangxi.42.1% of the Tropical Depression which enter affected areas of Guangxi can bring ainstorm and rainsorm above to Guangxi.(4)" Rammasun" moved northward with the Tropical Convergence to the coastal area of South China.The Southwest monsoon is involved in the connection with the circulation of the " Rammasun ",which makes the " Rammasun " obtain sufficient water vapor and unstable energy.Before and afte entering the Beibu Gulfr,the central vorticity and divergence have little changed,the vertical lifting speed increases,and the water vapor transport is full,and the strong convergence of water vapor,all are the main causes of torrential rain.The distribution of land and sea,and the topography of the Shiwan Mountain,play an important role in the torrential rain and heavy rainstorm of the coastal areas and the southern side of the Shiwan Mountain.(5)The Shiwan Mountain is break off rainstorm which caused by the " Rammasun" typhoon itself.After the typhoon crossed the Shiwan Mountain,the rain masses was loose,the rain intensity weakened,and the range of rainfall became wider.At the same time,the topography of the Shiwan Mountain has an effect on the " Rammasun" precipitation,which is one of the main reasons for the extreme precipitation in Fangchenggang.(6)Regional numerical model WRF3.4.1,The numerical tests for control and sensitivity were done against the Shiwan Mountain,It indicate:(1)WRF model can better simulate the movement path,landing site and spatial distribution of precipitation of " Rammasun".The northerly winds in the north site of the Shiwan Mountains,and the southerly winds in the south site are subjected to uplift by the terrain.Vertical and upward movements in the middle and lower layers are formed on the north and south sides of the mountain range,which is conducive to the emergence of heavy precipitation.(2)After removing the Shiwan Mountains,the landing site of " Rammasun" was eastward,and the moving path was southerly to the west.In addition,due to the northerly position of the lower center of the typhoon,and the south wind moves northward,the topographic uplifting effect weakened and disappeared.In addition,the water vapor convergence near by the mountains weakened,and the precipitation intensity decreased,the maximum reduction was more than 40 mm.(3)The presence of topography affects the typhoon movement path on the one hand,which affects the spatial distribution of the circulation.On the other hand,the disappearance of the topographic blocking effect makes the lower wind speed uplifting and weakening.The joint action of the two sides weakens the precipitation around the mountains.