Effects Of The Arctic Oscillation On Winter Precipitation In The Eastern Qinghai-Tibet Plateau

Based on the China gauge-based monthly gridded data(CN05.1)and the precipitation dataset provided by the Global Precipitation Climatic Center(GPCC)and ERA-interim monthly reanalysis data from 1979 to 2015,this paper analyzes the regional difference of winter precipitation in the eastern Tibetan Plateau(referred to as the TP)and the response of its interannual variation to the Arctic Oscillation(AO)anomaly by using regression and composite analysis methods and the effects of AO and ENSO on the precipitation in the South TP are discussed.The main conclusions are as follows:(1)The winter precipitation in the north and south of the TP is closely related to the AO,but the climate difference between the north and the south of the TP is obvious.The average precipitation in the North TP is only one sixth of that in the South TP,while the altitude in the South TP is only half of that in the North TP.The intensity of water vapor input and output in the North TP is weak,which is only one-third of that in the South TP.The climate trend of precipitation in the two places is also different.In recent decades,the North TP is getting wet,and the South TP is getting dry.The interannual variation of the two places is not synchronous,especially when there is more precipitation in the North TP,the correlation of precipitation between the two places is worse.(2)The variation of winter precipitation over the North TP is mainly related to the East Asian winter monsoon.When the AO anomaly is positive,the East Asian Winter Monsoon weakens and the tropospheric layers are southeast wind anomaly,which is conducive to the westward transport of warm and humid water vapor from the Western Pacific to the TP.The low-level zonal wind convergence,the high-level meridional wind divergence and terrain uplift lead to the increase of precipitation in the North TP.vice versa.(3)The variation of winter precipitation in the South TP is mainly related to the anomaly of the Southern Branch Trough.When the AO is positive,the strengthening of the South Branch trough is favorable for the warm and humid water vapor from the Bay of Bengal to move northward to the TP,the meridional wind convergence(divergence)in the low(high)layer increases the atmospheric instability,and the ascending motion increases,resulting in the increase of precipitation in the South TP.vice versa.Compared with the North TP,the thermal effect in the South TP is more obvious.(4)AO can affect the East Asian Winter Monsoon and the South trough respectively through the sorth and south wave train,and change the zonal wind and meridional wind,and then affect the north and south TP winter precipitation.The negative AO anomaly has more significant effect on winter precipitation than the positive AO anomaly.(5)ENSO is only related to precipitation in the South TP.When ENSO is positive,there is an obvious westerly jet in 15°N,which can carry the warm and humid water vapor from Bay of Bengal to the south TP,and vice versa.The effect of ENSO on precipitation in the South TP is asymmetric,and the significant effect is in its positive phase.(6)There is a weak negative correlation between AO and ENSO,which is the reason for the enhanced correlation between AO(ENSO)and precipitation in the South TP after removing ENSO(AO)signal.AO and ENSO can synergistically affect the precipitation in the South TP,and their effects are asymmetric,which is related to the asymmetric effects of AO and ENSO on the precipitation in the South TP.