Research On The Impact Of PDO On Winter Temperature And Precipitation In The Qinghai-Tibet Platea

As external factors,oceanic modes can affect the atmospheric circulation between the Tibetan Plateau and oceanic regions,as well as the vertical and horizontal motion of the atmosphere above the Tibetan Plateau.As an important interdecadal scale signal,the Pacific Decadal Oscillation(PDO)has an important influence on the global climate,especially the summer precipitation in East Asia and the dry and wet changes in China monsoon region.Based on the CN05.1 dataset,the observational snow depth dataset for the Tibetan Plateau released by the National Tibetan Plateau Data Center,ERA5 reanalysis dataset,the monthly sea temperature data from the Met Office Hadley Centre over the period 1962–2018,this paper investigates the interdecadal variation of winter temperature and precipitation in Tibetan Plateau,and the influence of the PDO on the winter climate on the Tibetan Plateau and the related physical mechanisms.We also analyzed the long-term(1200 years)pi Control simulation output from the Community Earth System Model Version 2(CESM2)within the Coupled Model Intercomparison Project Phase 6(CMIP6).The main conclusions are as follows:(1)The phase transition of PDO has a significant impact on the winter temperature and precipitation on the Tibetan Plateau.The surface air temperature and precipitation averaged over the Tibetan Plateau in winter both have clear interannual and interdecadal variations.On the interdecadal scale,their variations seem to be related to the transition of the PDO phase.The results showed that changes in the phase of the PDO have a significant effect on winter temperatures and precipitation over the Tibetan Plateau.The positive PDO phase increases winter precipitation,leading to the increase of snow depth and total cloud cover,which,in turn,affects net surface shortwave radiation during the positive phase of the PDO.The surface air temperature of the Tibetan Plateau is then decreased as a result of the reduction in the net surface shortwave radiation.(2)With the analyse of the interdecadal changes in the atmospheric circulation over the Tibetan Plateau.The results show that the differences in the 200 and 500 h Pa winds are characterized by an anomalous cyclone over the Tibetan Plateau and the Bay of Bengal,which favors the transport of water vapor.(3)Our analyses of the moist static energy showed that the horizontal advection of anomalous moist enthalpy by the climatological zonal winds was responsible for anomalous ascending motion over the Tibetan Plateau.This is mainly caused by warming of the tropical troposphere over the Indian Ocean during the positive phase of the PDO.The PDO therefore has an important modulating role in the interdecadal variability of the winter climate over the Tibetan Plateau.