Characteristics of the Difference of Temperature between Surface and Atmosphere over the Tibetan Plateau in the Early Stage of East Asian Summer Monsoon Onset

Using the observational air and surface temperature datasets of 112 stations in the Tibetan Plateau (TP) and around areas, the temporalspatial evolution characteristics of the difference of temperature between surface and atmosphere （Ts-Ta) over Tibetan Plateau in the early stage of East Asian Summer Monsoon(EASM) onset and its connections with the EASM are analyzed by EOF(Empirical Orthogonal Function), REOF (Rotated Empirical Orthogonal Function), and other methods. The results show that, the time when Ts-Ta in TP reach the peak value of the year is one month ahead of that of the air and surface temperature, and about two months earlier than that of the same latitude in the middle and eastern China. During the transition season, the sensitive area of Ts-Ta in TP gradually shifts from the central in March to the southeast part in April, and after its 〖JP〗range expands in May, it maintains a stable state in the southeast part of TP. In April and May, the early stage of EASM, snowmelt and thawingfreezing processes of soil over TP have significant effects on the sensitive distribution of Ts-Ta. The trend of Ts-Ta in TP in April is entirely different from that in May. In April, the radiation cooling caused by snow albedo has affected on the change of surface ground, leading to Ts-Ta of TP decreases from the 1960s to the mid-1970s, afterwards it always keeps a rising trend from the late 1970s through the 1990s. During a period from the 1960s to the 1990s, Ts-Ta of TP in May more reflects the effect of diabatic heating over TP, and appears the decreasing trend.