东亚夏季风建立前青藏高原地气温差变化特征

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

利用青藏高原地区112个站1980~2001年和部分站点1960~2000年的气温、地温资料,采用经验正交EOF和旋转经验正交REOF等方法,对东亚夏季风爆发前青藏高原地气温差的变化特征进行分析,并对其与东亚夏季风之间的联系进行了分析。结果表明,青藏高原地气温差一般超前气温、地温1个月达到全年最大值,比中国中东部同纬度地区的地气温差达到最大值超前2个月。随着高原由春季向夏季的过渡(3~6月),高原地气温差年际变化的异常敏感区逐渐由3月中部的河谷地带移动到高原的东南部地区。高原地表积雪的融雪过程和冻土的融冻过程对东亚夏季风建立前期高原4、5月份地气温差具有重要影响。高原地区的地气温差在4、5份的呈现出不同的变化趋势。4月份,由于积雪的反照率引起的辐射冷却作用,地气温差在1960年代到1970年代中期呈显著减小趋,之后呈增大的趋势。1960年代到1990年代5月的地气温差更多地反映出非绝热加热的作用,高原地气温差呈减小趋势。

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） on- set 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 Chinm 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 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 T^- T~. The trend of Ts- T~ 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 diabatie heating over TP, and appears the decreasine trend.