Analysis Of Water Vapor Sources In Nagqu Region Of Qinghai-Tibet Plateau

As the Asian Water Tower,it's of great significance to study the precipitation sources of the Qinghai-Tibet Plateau for water security and water resources utilization in China.Naqu area,located in the northern Tibet Plateau,is the birthplace of many rivers or the flowing place of tributaries.It is rich in glacial melt water and groundwater resources,providing sufficient water for the surrounding and downstream areas,and is an important research area of atmospheric water cycle.In this paper,the FLEXPART Lagrangian model driven by FNL data and the HYSPLIT Lagrangian model driven by GDAS data are used to analyze the moisture transport track and the track of different grades of precipitation in summer of 2014 in Naqu area.Using the cluster analysis to get the moisture passages and the particle tracking analysis to calculate the moisture contribution.The results show that,there are obvious monthly and ten days changes in the moisture transport trajectories in summer,which is mainly caused by the northward advance of summer monsoon.The Indian Ocean,the Arabian Sea,the Bay of Bengal,the Atlantic Ocean and Central Asia are the five main moisture transport passages.The moisture from Central Asia is the main contributor of Naqu precipitation,followed by that from the Arabian Sea.There are southern and western paths for light rain and moderate rain,but only southern paths for heavy rain.The moisture transport in the ocean plays a decisive role in the precipitation level.The area with high moisture source one day ago is the Yarlung Zangbo River Basin.The area with high moisture source three days ago is the border between India and Badan.The moisture source of heavy rain is more concentrated than that of light rain and moderate rain.There is a good correspondence between the region of moisture contribution concentration and the end point of moisture trace.In a nutshell,the moisture sources of different grades of precipitation are different.By using the method of comprehensive analysis and Lagrangian model simulation,a heavy rainfall in Naqu caused by the plateau vortex is analyzed.The source of moisture in Naqu area is determined and the contribution of moisture source area to the summer rainfall in the study area is further quantified.The results show that the ascending motion Over Naqu is strong,the positive vorticity of the low layer corresponds to the negative vorticity of the high layer,the convergence of the low layer corresponds to the divergence of the high layer,and the moisture is abundant and there is convergence of the moisture Over Naqu.During the precipitation period,the convective activity is very strong,there are many strong convective cloud clusters,and the strong ascending motion in the cloud makes the small particles rapidly collide and grow into raindrops,forming a short-term strong falling Precipitation.Most of the target gas blocks affecting precipitation come from the relatively low atmosphere south of the target area,which can be traced back to the Bay of Bengal,the Arabian Sea and the Indian Ocean.In addition,a small part of the target gas blocks along the western route of the Qinghai Tibet Plateau come from the middle and lower atmosphere.The highlevel water vapor is mainly transported by the South Asia high anticyclone.A few gas blocks come from East China and South China Sea.The moisture transport in the West and South borders is the main source of this heavy rainfall in Naqu,and the moisture source areas are mainly the Indian Ocean,the Arabian Sea,India,the Bay of Bengal,Xinjiang and Central Asia.The moisture from the Indian Ocean and the Arabian Sea plays a key role in the precipitation,while the local moisture contribution is ignored.