| Based on the daily precipitation datasets in the Tibetan Plateau?TP?from 1979 to2016,the spatial-temporal variation characteristics of precipitation and inhomogeneity are analyzed with statistical methods.Combined with NECP reanalysis data and HadISST data from Hadley Centre for Climate Prediction and Research,the key areas of the Indian Ocean and it's impact on the circulation field are studied,which had affected the summer precipitation in the TP.The conclusion was showed as follows:?1?The spatial distribution of annual mean precipitation decreased from southeast to northwest in TP.More rainfall areas were located in west Sichuan Plateau,Nyingchi,the southern foot of Himalayas,Three River headwaters region,Hehuang valley,Less rainfall areas were located in Qaidam Basin and northern TP.The precipitation of Qinghai lake,Source Region of Yangtze River and northern TP were significant increased,but it decreased in northern Sichuan Plateau,downstream areas of Yarlung Zangbo river and the southern foot of Himalayas.Nyalam,downstream areas of Yarlung Zangbo river and southeast of Sichuan Plateau were always more rainfall areas in four seasons,it extended in summer.The precipitation of southeastern TP was obviously increased in spring,it is significant inceased in Qinghai lake,Source Region of Yangtze River,midwest Tibet in summer,it was slightly increased in Qinghai in autumn,but there was no change in winter.?2?The decadal anomalies of precipitation reduced firstly and then increased in TP,.It was rainy in southern TP and less rainfall in northern TP in the 1990s,but it was opposite in the 2000s.The annual precipitation increased with an increasing rate of6.5mm·?10a?-1 in TP,the increasing rate of spring was 4.8mm·?10a?-1.The rainy and dry season was clear.It is different in Bowo and Nyalam,which monthly variations were bimodal type.?3?The interannual variation and spatial difference of precipitation concentration degree?PCD?and precipitation concentration period?PCP?were significant in TP.PCD ranged from 0.61 to 0.71,it's average value was 0.66.PCP ranged from 38 to 41 pentad,it's average value was 39.9 pentad.The distribution of precipitation in each divided zone was very uneven,the rainfall of southern plateau was the most concentrated and PCP was also the latest,but the rainfall of northeastern plateau was relatively even.PCD and PCP had the largest interannual fluctuations in northwestern TP.The correlation between precipitation and PCD was the most positive in Ali,but it was negatively correlated in Nielamu.The correlation between precipitation and PCP was positive in east part of 90°E and negative in west part.PCD and PCP of more rainfall years were both bigger than less rainfall years.?4?Pre-November to Pre-December was the key period when the Indian Ocean sea surface temperature anomalies?SSTA?had been affected summer precipitation in TP.The key areas of Indian Ocean were northwest of equatorial Indian Ocean?60°-70°E,10°-EQ?and southeast of equatorial Indian Ocean?90°-110°E,10°S-EQ?.When sea surface temperature of western key areas was warmmer than the eastern,there was more rainfall in Tibet,southwestern Sichuan Plateau and northeastern TP.?5?In lower troposphere,South China Sea?SCS?summer monsoon strengthened in positive Indian Ocean Dipole?PIOD?years,but SCS Summer Monsoon got weaker and the Indian monsoon enhanced in negative Indian Ocean Dipole?NIOD?years.In the middle troposphere,the intensity of Balkhash blocking high,Lake Baikal trough and subtropical high over the western Pacific were more stronger in PIOD years.In upper troposphere,there were meridional circulation in PIOD years and zonal circulation in NIOD years.In PIOD years,the vapor transported from a converging southerly airflow,which an easterly airflow form the Bay of Bengal and a westerly airflow form south side of the subtropical high converged in sourthern Yunnan.It was entirely different in NIOD years,vapor came from a easterly airflow from northwestern Pacific Ocean. |
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