Characteristics Of Drought/Flood And Water Vapor Resources Over The Eastern Yunnan During Spring

The main aim is to analyse the characteristics of drough and flood and moisture distribution over estern Yunnan during spring.lt is also analysed and modelling that the influence of Yunnantopographty on regional drough/flood. on the activities of mian precipitation systems. on the moisture resource distribution.Yunnan is divided into three regions by REOF method based onannual spring rainfall, then the location and area range of the eastern region is determined. The index of PDS1is chosen to describe the drought and flood of the eastern Yunnan after comparing with the other two kinds of drought index only based on rainfall. By applying Morlet Wavelet Method, an obvious14a long oscillation period is found for the53a drought and flood time series in spring over the eastern Yunnan, and the time series can be divided into three periods:1958to1980is drought period,1981to2000is flood period, after2000is another drought period.There are two mainly ways transport in water vapor resource of Yunnan:(1) The way of eastward water vapor transport come from Bengal:(2)The way of south water vapor transport come from the Picific subtropical high;(3) The distribution of Atmospheric Precipitable Water is type of “U”, the atmospheric precipitable water reduce from high altitude to low altitude in Yunnan. The synthetic analysis of drought and flood over eastern Yunnan shows that there are two parallel zonal waves in the circulation background deviation fields of geo-height, zonal wind and air temperature. In the flood years, the high latitude wave is positive and the mid-latitude wave is negative for geo-height deviation field at500hPa, it shows that low systems are active over Yunnan. For zonal wind deviation field at500hPa. the high-mid latitude wave is minus and the mid-low latitude wave is plus, it shows that south branch trough at south of Tibet is strong at both velocity and amount transferring moisture. The temperature deviation field at700hPa. the high latitude wave is positive and mid latitude wave is negative, it shows that the temperature over Yunnan is lower than normal and forms temperature front with the warm and humidity air mass of sub-tropic-high at low latitude ocean. It will help to generate front precipitation at the eastern Yunnan. In drought years. the all element characteristics are opposite to flood years for the two parallel zonal waves at deviation fields. It needs to be emphasized that when the upstream zonal wind is blocked by west-south boundary of Tibet plateau, a southward refraction will happen. The strong wind of the flood years and the weak wind of the drought years will directly impact the strength of the south branch tough. the upstream wind strength and the strength of south branch trough are proportional. The key system of precipitation in eastern Yunnan during spring is Kunming quasi-stationary front. Within the background deviation waves, the front shows that the happen frequency and duration are higher and longer during flood years than drought years. The water vapor resources and vapor flux is significantly greater during flood years than drought years. We analyze the geographic distribution of water vapor and Kunming quasi-stationary in typical drought year (2010) and flood year (2000). The result shows that:(1) The vapor flux of northeastern Yunnan is greater during the flood year than the drought year, and the distribution of vapor flux is opposite in northern Yunnan;(2) The atmospheric precipitable water is greater during the flood year than the drought year;(3) The position of Kunming quasi-stationary is more northerly and concentrated with a wider range of activities, the days of quasi-stationary is significantly longer during the flood year than the drought year. When Kunming quasi-stationary front maintaining, we analyze the distribution of meteorological elements in spring of2010,2000.The result shows that:the temperature and cloud cover is lower, and humidity is higher in2000, it shows that Kunming quasi-stationary front is stronger than the drought year. By discussing circulation background46cases Kunming quasi-stationary front.we get three typical circulation patterns:(1) One ridge with two trough, there are19cases which account41%of the total statistical cases;(2) Moving eastward of the trough, there are14casesin all of cases;(3) Crashing of blocking high, there are13cases in all of cases.In order to analyse the effect of Yunnan land to water vapor distribution, we analysis and simulate a strong precipitation process with Kunming quasi-stationary front on December13-17,2013. We find that WRF could simulate the shear line, Kunming quasi-stationary front precipitation successfully. By the sensitivity experiment of halving land of Yunan, we get the results:(a) the water vapor increased in Northwest of Yunnan, and the water vapor transport belt move to northward, more water vapor could get to middle and northern of Yunnan. The effect is in touch with weather system of topography on water vapor transportation and precipitation in North Yunnan. When the effect of eastern terrain reduced, the cold air could reach to south of Yunnan easily, and moist air could reach to Eastern Yunann likely. As a result, the cold air of Eastern Yunann decreased significantly, then Kunming quasi-stationary front disappeared, the precipitation of Eastern Yunann changed.(b) When the topography of Eastern Yunnan reduced to1500m, the ground temperature rised, and the wind shear changed in eastern Yunnan. The impact on the Kunming quasi-stationary front is very significantly, the distribution of water vapor and precipitation in eastern Yunnan increased obviously, the warm humid air will improve the water vapor resource by changing of Eastern Yunnan topographic.