Characteristics Of Gravity Wave In The Eastern Tibet Plateau And The Relationship With Southwest China Vortex Activity

This thesis summarized the activity characteristics,motivation conditions and meteorological significance of gravity wave,especially,the close relationship with mesoscale weather disasters,such as torrential rain since the 1960 s,and reviewed the research advances of the structural characteristics and development mechanism of Southwest China Vortex.On the above bases,it is found that the steep terrain of eastern Tibetan Plateau is not only the concentration of Southwest China Vortex source,but also easy to motivate Gravity Wave.Therefore,for this problem if there is some connection between Gravity Wave and Southwest China Vortex.In the paper,using the data from the experiment of intensive observation of Southwest China Vortex at the eastern side of Tibetan Plateau during 2012-2015,the parameters of Gravity Wave are calculated and its characteristics are analyzed over Jiange,Jinchuan,Jiulong,and Mingshan stations by Hodograph method,and the rules of both Gravity Wave process and Southwest China Vortex activity are researched,and the characteristics of the atmospheric circulation affecting the moving of Southwest China Vortex are studied.The main conclusions are as follows:(1)The gravity wave source has obviously regional difference at the eastern side of Tibetan Plateau.It is are mainly at the lower troposphere at the north and middle part of the eastern side of Tibetan Plateau,especially in the region with the great elevation fall between eastern edge of the Plateau and the western margin of Sichuan Basin,where it account for two thirds of the total at the lower troposphere,the wave sources of upper troposphere are more important in the low-lying area of the southeast edge of the Plateau such as Jiulong station.(2)There are some obvious differences in intrinsic frequencies and horizontal propagation direction.The intrinsic frequencies mainly concentrate in the range of1~3f at Jiange in the northeastern margin of Western Sichuan Plateau,Jinchuan in the middle part of it and Mingshan station in the eastern margin of it.But,the intrinsic frequencies of Jiulong station are concentrated in 1~3.5f in the southern part of it atthe eastern side of Tibetan Plateau.(3)The differences of horizontal propagation direction of gravity wave are also obvious in the above four stations.It is mainly south direction at Jiange station,the performance is isotropic at Jinchuan station.The Jiulong station mainly points to the northwest and southeast showing a significant nonuniformity,and both of the north and the east is the dominant propagation direction at Mingshan station.Then,there is no significant interannual variation in wave energy of gravity wave.(4)Some significant differences for Gravity Wave exist during the different activities of Southwest China Vortex.In the early period of moving vortex activity,the propagation direction of Gravity Wave in horizontal is mainly northeastsouthwest,the probability of its upward propagation is greater than downward propagation,and kinetic and latent energy of it is relatively strong with large amplitude.But for stagnant vortex,the initial propagation direction is mainly northwest-southeast,the probability of its upward propagation is equivalent to its downward propagation,and the kinetic and latent energy of it is relatively weak with small amplitude.Furthermore,the horizontal propagation direction of Gravity Wave has also indicative significance for the moving direction of Southwest China Vortex.(5)The Gravity Wave can be divided into the diurnal one and the nocturnal one according to the emerging time of it.At the initial time of nocturnal Southwest China Vortex,the nocturnal Gravity Wave emerges(20:00PM to 8:00AM)with higher probability.It indicates that the nocturnal behavior for both of them may has some relationship between the emerging time of Gravity Wave and Southwest China Vortex.(6)The invasion of cold air in the middle and upper level is the key factor to affect the Southwest China Vortex moving,and its related factors such as the increase of atmospheric baroclinicity caused by the decrease of geopotential height have an important fact for the Southwest China Vortex moving.The westerly deviation of moving vortex also indicates that the ascending motion in the lower of its east side with the compensation sinking airflow in its source is more favourable to the development of the vortex eastwards.