Characteristics Of Multiscale Air-Land Interaction Over Tibetan Plateau In The Summer Of 2014

Through the station observation data provided by China Meteorological Administration?JRA-55 and GPCP daily Reanalysis data?original data of 3m eddy correlation system and 10Hz turbulence data based on "The 3rd Tibetan Plateau atmospheric scientific experiment" in July and August of 2014,described the basic climate feature of Tibetan Plateau in July and August of 2014,such as,high and low circulation fields?precipitation?Tibetan Plateau Summer Monsoon.Then,selected stations which existed 10?20-day low frequency oscillation,there are Shiquanhe station and Linzhi station which respectively located in southwest and southeast of Tibetan Plateau area,analysis of low frequency oscillation propagation and evolution characteristics of strong ISO cases.At last,discussed the variation characteristics of the surface layer micro climate,respectively.The fundamental conclusions in the thesis are summed up as follows:(1)In the troposphere high-level 200hPa,South Asian High drooling over the Tibetan Plateau in July and August of 2014,its range is larger than mean state.The upper level jet stream is very small in July,it is eastward-moving in August,reaching the north edge of Subtropical High,and there is a small range of north westerly jet in the high latitude.However,in the lower troposphere 500 hPa,the Subtropical High in July and August of 2014 is stronger and more west than mean state.In the middle and high latitude,the type of July is two-through and one-ridge,Tibetan Plateau located before through and after ridge.The type of August is a weak through,Tibetan Plateau located after through.(2)Tibetan Plateau Summer Monsoon in 2014 is starting from 15 pentad and ending from 62 pentad,the time of outbreak is earlier than climatological mean values and the end of time is delayer,so,the whole time of monsoon is lasting long.The daily precipitation of Tibetan Plateau in 2014 is more than climatological mean values(1979?2014).(3)Shiquanhe station and Linzhi station which respectively located in southwest and southeast of Tibetan Plateau area,existed 10?20-day low frequency oscillation.(4)The 10?20-day low frequency component of high and low circulation fields?water vapor fields?heat sources and surface sensible/latent heat flux in the Shiquanhe station and Linzhi station are opposite during its dry or wet phase,respectively.During two stations respective dry(wet)phase,convergence(divergence)at 200hPa,sink(rise)at 500hPa,this configuration is not conductive(good for)producing precipitation,the water vapor is divergence(convergence),heat sink(heat source).In the Shiquanhe station,dry(wet)phase low frequency surface sensible heat flux is negative(positive)anomaly,low frequency latent heat flux is positive(negative)anomaly,in the Linzhi station,dry(wet)phase low frequency surface sensible heat flux is positive(negative)anomaly,the same as low frequency latent heat flux,therefore,the different variation of low frequency surface sensible/latent heat flux have influence on precipitation,this influence has different performances in west and east Plateau,respectively.(5)From 10?20-day low frequency time-longitude section we can see that the low frequency oscillation of Shiqianhe station is propagates from west to east,but in Linzhi station propagating from east to west,the precipitation anomaly of two station are affected by different regions.For this reason,there are two kinds of different origins of low frequency oscillations.(6)Surface layer meteorological elements and turbulent flux have obvious diurnal variation in the dry and wet phases.Usually,the highest temperature appeared at two o 'clock in the afternoon,but in the dry and wet phase of Shiquanhe station,it appeared at eight o 'clock in the evening.In the Shiquanhe station,the specific humidity during dry and wet phase have the same trend of variated,but it is contrary in the Linzhi station.The momentum flux?sensible flux?latent flux are all presented the type of single-peak.From Bowen ratio,we can see that in Shiquanhe station wet phase dominated by latent heat throughout the day,dry phase dominated by latent heat before 6 a.m.and takes a leading by sensible heat after 6 a.m..In Linzhi station,wet and dry phase are all lead by sensible heat before 8 a.m.and dominated by latent heat after 8 a.m..The average kinetic energy of turbulence and average wind speed are positive correlation in two stations,when average wind speed are reaching maximum,it is time that the average kinetic energy of turbulence are strongest.The vertical momentum is transported downward,heat and moisture are upward.