The Characteristic Of Summer Precipitation Over The Tibetan Plateau And Its Response To The North Atlantic Oscillation

The Tibetan Plateau(TP)is an important area for global climate change and the precipitation over the TP plays a crucial role in the local and the northern hemisphere water cycle.In this study,the station data provided by the National Meteorological Information Center,12 precipitation datasets and the atmospheric fields from 8 reanalysis datasets are used to investigate the characteristics of the summer precipitation over the TP and its relationship with the large scale water vapor transport.Meanwhile,the impact of the North Atlantic Oscillation(NAO)on the precipitation over the TP is also explored.The conclusions are summarized as follows:(1)Light rainfall(LR),moderate rainfall(MR)and very heavy rainfall(VHR)over the TP account for 3.5%,28.4%,and 6.8% of the total summer precipitation,respectively.According to the cumulative probability distribution function of rainfall frequency and amount,most datasets overestimate the frequency of LR and VHR,and underestimate the MR frequency with largest deviation occurring in the characterization of the VHR.Considering the performance of all the datasets for depicting all precipitation levels,APHRO is the best,followed by JRA55 and CMAP,while GPCC is more accurate when portraying LR and MR.(2)The TP is the sink of water vapor in summer,and the convergence of water vapor is mainly caused by water vapor advection,while the wet advection term and the wind field convergence term cause the convergence of water vapor in the middle part.The anomaly of the precipitation in the southeastern TP is mainly caused by the abnormal anticyclone water vapor transport from the Indian peninsula to the Bay of Bengal.(4)The annual precipitation and the precipitation in each season show a decreasing trend with the increase of altitude,and the standard deviation of each altitude level shows a decreasing trend with the increase of altitude.The annual precipitation and precipitation in each season in the southern part of the TP decrease with increasing altitude,and the opposite is true for the stations over the northern TP.(5)Further study of the relationship between the North Atlantic Oscillation and the summer precipitation,it is revealed that there is a significant positive correlation between the NAO in December and the summer precipitation over the TP,and the main mechanism is concluded as follows: NAO in December excites the tripolar mode of the North Atlantic sea surface temperature,which continues until the spring.Therefore,the tripolar mode in May is regarded as the early signal of anomaly for the precipitation in June.When this mode is in positive phase,the water vapor transport in the southwestern and southeastern TP increases,so does the vertical water vapor transport.This strengthens the precipitation in this area,while evaporation and meridional water vapor transport make negative contribution.In addition,the evaporation,the vertical and meridional transport of water vapor in the northeastern TP increase,which cause the precipitation increase here.