The North-South variation and mechanism of the precipitation over the Tibetan Plateau during the monsoon in the past 60 years

Tibet plateau plays very crucial roles in globle climate system, and the precipitation is  one of the main factors in Tibet plateau climate system, Based on GPCC monthly precipitation data and ERA5 monthly precipitation reanalysis data from 1961 to 2016, this study analyzes the spatio-temporal distribution and evolution of plateau precipitation during the May-September monsoon period under the background of global warming. Try to analyze the mechanism reason affecting precipitation variation in different regions. The precipitation in the South part of Tibet plateau began to increase in May, and advance to the northwest part of Tibet plateau during the July and August, and began to back to the south in September. According to The decomposition of the empirical orthogonal function (EOF), we divided the Tibet plateau into north and south two parts by the mount tunggula, on the interannual variability, percentage of precipitation in the monsoon plateau exists reverse change relation, precipitation showed a trend of slight decrease in the south part of plateau, plateau in northern precipitation shows ascendant trend on decadal scale, rate of precipitation in the plateau there are shocks between 3 to 5 years in 7-9 or 11 years. There is a north-south inverse change rate in the precipitation in the plateau during the monsoon period. The analysis of the relationship between the monthly precipitation data and the atmospheric circulation in the south and north of the Plateau shows that the precipitation in the south of the Plateau is affected by the South Asian monsoon, while the precipitation in the north of the plateau is related to the Rossby wave of the subtropical westerly jet. In other words, the precipitation in the southern part of the plateau is mainly controlled by summer risk, while the precipitation in the northern part of the plateau is affected by subtropical westerly winds.

 

Keyword: Tibetan Plateau，Precipitation，Circulation，South asia monsoon，Jet stream