青藏高原南部冰芯记录与大气环流的关系*

通过念青唐古拉峰拉弄冰川垭口处(30°24'30″N, 90°34'12″E;海拔5850m)长度为29.5m的冰芯记录,恢复了1952~1998年间大气降水δD和净积累量的时间变化序列。上述两组序列与NCEP/NCAR气候资料的相关分析表明:δD和净积累量与中亚冬季的气压、南亚和青藏高原冬季、夏季的位势高度关系密切。中亚地区冬季气压的升高以及冬、夏季南亚和青藏高原位势高度的异常增强了印度夏季风,导致了念青唐古拉峰地区20世纪80年代以来降水量的增多和降水中δD值的降低。根据念青唐古拉冰芯δD和净积累量记录及其与亚洲地区大气环流的关系,可以通过青藏高原南部较长的冰芯记录来恢复过去该地区大气环流变化的历史。

RELATIONSHIPS BETWEEN AN ICE CORE RECORDS FROM SOUTHERN TIBETAN PLATEAU AND ATMOSPHERIC CIRCULATION OVER ASIA

Hydrogen isotope (δD) and annual accumulation records covering the period A.D. 1952~1998 were reconstructed using a 29.5m ice core from the col of the Lanong Glacier (5850m a.s.l.) on the eastern saddle of Mt. Nyainqêntanglha (NQ), Southern Tibetan Plateau (TP). Using NCEP/NCAR Reanalysis data, we explore the relationships between the annual δD and accumulation records from the ice core and primary components of the climate system. Linear correlation analysis between δD and climate components indicates that δD variations are correlated with summer precipitation, winter surface pressure, and geopotential height in both winter and summer over the South Asian and TP region. Summer precipitation and δD are negatively correlated over regions of northern India and the Bay of Bengal, while a positive correlation exists over the north of TP. This is consistent with the amount effect controlling δD values during the summer monsoon season. A negative relationship between δD and winter surface pressure over central Asia suggests that high pressure acts as a barrier against winter moisture transport with higher δD values from the Westerlies. Negative correlations between δD and geopotential height in both summer and winter over Asia indicate that stronger atmospheric circulation over Asia corresponds to lower δD values. Linear correlation analysis between annual accumulation and climate components for the 47 year overlap periods indicates that annual accumulation variations are closely correlated with sea surface and 500hPa air temperature over the North Indian Ocean and atmospheric circulation (surface pressure and geopotential height) over Asia. An Intensification of atmospheric circulation and increase of sea surface and air temperatures, resulting in intensified moisture availability and moisture transport, have been a major cause for the increase of ice core accumulation over the Mt. NQ region since the 1980s. Associations between atmospheric circulation and the NQ δD and accumulation records found in this study can be applied to future studies utilizing longer ice core records to reconstruct atmospheric circulation farther back in time.