| Based on the ERA-Interim daily mean reanalysis data of temperature field from 1980 to 2015,it is investigated that the spatiotemporal characteristics of whole-layer(ground to 100 h Pa),high-layer(550~100h Pa)and low-layer(ground to 550 h Pa)temperature vertical gradient above three representative region of Tibetan Plateau(TP).Then,the characteristics of temperature vertical gradient with increasing height from 350 to 200 h Pa are analyzed,and the reasons for this phenomenon are further discussed.The results are following:(1)The seasonal variation of temperature vertical gradient be found over the TP,that is,in winter and spring,the temperature of 550~200h Pa and 150~100h Pa over the TP decreases slowly with the rise of the altitude,and the temperature of 200~150h Pa decreases rapidly with the rise of the altitude;in summer,the temperature of 550~200h Pa over the TP decreases rapidly with the rise of the altitude,while the temperature of 200~100h Pa decreases slowly with the rise of the altitude,and the inversion layer appears around 100 h Pa;in the autumn,with 90oE as the boundary,the temperature of 550~100h Pa decreases slowly with the rise of the altitude in the western part,and the temperature of 550~300h Pa decreases rapidly with the rise of the altitude in the eastern part,while it decreases slowly at 300~100h Pa.(2)In spatial distribution,the temperature vertical gradient of whole-layer gradually decreases from west to east in each season,which in summer is large and in winter is minimum.The high-layer temperature vertical gradient shows “high in the south and low in the north” and there is no significant difference in the east-west direction.For the low-layer,temperature vertical gradient has obvious seasonal variations.In temporal variation,the annual variation of the TP main body temperature vertical gradient varies from the other two regions.The TP inter-annual variation of the temperature vertical gradient in high-layer is more significant in winter and spring,and the inter-annual variation is manifested in different degrees of decline after 21 st century.The annual variation of the temperature vertical gradients in the eastern and western parts of the TP is broadly consistent,showing a “double-peak” pattern.(3)The vertical atmospheric heat source over the TP is not evenly distributed throughout the whole layer.Heat source characteristics is obvious at the TP edge.From the correlation analysis of the vertical heat gradient and the temperature vertical gradient of the whole layer,the upper layer and the lower layer,it is concluded that the stronger the effect of the non-adiabatic heating(cooling),the smaller(larger)the temperature vertical gradient,the smaller(larger)the reduced degree of the temperature decreases with the rise of the altitude.The non-adiabatic heating(cooling)is the main factor that causes the temperature to decrease slowly(quickly)with the rise of the altitude in the whole layer of the TP.(4)In terms of the vertical variation of the temperature vertical gradient in the three representative areas of the TP,the temperature vertical gradient shows a “two increases and two decreases” pattern with the rise of the altitude,in spring,autumn and winter.However,the summer the vertical variation of temperature vertical gradient varies from the other three seasons,that is,it appears increase with the rise of the altitude in the middle and upper troposphere.According to the monthly and pentad variation of the temperature vertical gradient in summer,it is concluded that the temperature vertical gradient in the western part and main body of the TP increasing with the rise of the altitude occurs on 36 th pentad and disappears on 51 st pentad,at 350~200h Pa.In the eastern part of the TP,the temperature vertical gradient does not increase with the rise of the altitude.(5)The initial cause analysis of the 36 th pentad temperature vertical gradient increases with the rise of the altitude in the western part and main body of the TP revealed that the two ares are controlled by a belt-shaped high pressure at 350~200h Pa.In highlayer,the strong high-pressure divergence can take away the air column heat and also can lead to the heat dissipation increasing.Meanwhile,the anti-phase of the atmospheric annular wave mode appears in the western and eastern TP,that is,the anomalously strong mid-latitude easterly air currents and tropical westerlies,the anti-Hadley and anti-Ferrel circulations of local meridional circulations brings an unusually strong updraft from 20°N to 40°N.At 350~200h Pa,high-pressure divergence away heat and enhanced adiabatic rising cooling effect together caused the temperature decrease with the rise of the altitude in the western part and main body of the TP. |
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