亚洲夏季风环流及雨季进退的非同步性

Temporal Nonsynchronization of the Asian Summer Monsoon Onset and Retreat Between Wind Circulation and Rainfall

亚洲季风区雨季及高低空夏季风环流在建立、维持及撤退上存在着显著的时间差异,这种差异被称为"非同步性"。通过对1979～2006年CMAP降水资料及NCEP/NCAR再分析风场资料的分析,本文发现:(1)对于夏季风的建立,孟加拉湾中部至菲律宾海,低空850 hPa夏季西南风的建立日期明显要晚于雨季的开始,而阿拉伯海和印度地区雨季的开始则晚于夏季风的建立;对于200 hPa的高空环流,这种风雨非同步的关系与低空季风环流与降水建立的关系基本一致,但西北太平洋热带地区正好相反。(2)对于夏季风的撤退,低空850 hPa上,从75°E～125°E,夏季风的结束在雨季结束之前,其中孟加拉湾中部及南海中西部较为显著,而阿拉伯海中部以及菲律宾东南海域,雨季的结束远远早于(4～5个月)夏季风的撤退;对于200 hPa的高空环流,整个亚洲季风区夏到冬季型风场的转变要晚于雨季的撤退,但在15°N附近的印度半岛和中南半岛东部沿岸地区典型的春秋雨季转换区域,高空环流场的转换略早于雨季的终止。(3)南海北部地区,高空200 hPa环流表现出较为显著的冬夏季节翻转,与南海雨季的爆发联系紧密;印度地区雨季的开始与该处高低空异常Hadley环流的建立以及阿拉伯海上空夏季风的建立有密切联系,而与当地低空环流的季节性反转联系不大。

The onset,duration and retreat of rainy season are distinguished from those of summer mon-soon circulation in Asia,named as＂nonsynchronization＂.With defining the new concepts of wind onset and wind withdrawal,this study analyses the temporal discrepancies of seasonal variations of wind and precipitation in Asia using Climate Prediction Center Merged Analysis of Precipitation（CMAP） and the National Center for Environmental Prediction National Center for Atmospheric Researches（NCEP-NCAR） reanalysis data from 1979 to 2006.The results are as follows：（1） On summer monsoon onset,the south-westerly onset at 850 hPa is later than that of precipitation in the regions from the middle part of Bay of Bengal to Philippines.The opposite features happen in the regions of east and center part of Arabian Sea,the southern India and most parts of Southeast Asia.In terms of those between 200 hPa circulation and rainfall,similar results were obtained except for tropical regions of the western North Pacific.（2） In terms of the summer monsson retreat,the wind retreat are earlier than that of rainfall in the regions from 75°E to 125°E,especially in the middle of Bay of Bengal and the mid-western of South China Sea（SCS）,and vice versa.Compared with the retreat of 200 hPa circulation,the rainy seasons withdraw consistently earlier in entire Asia,except the regions where the equinoctial monsoon dominates.（3） In the north part of the SCS,the indication of summer reversal of 200 hPa circulation highly associated with the SCS sum-mer monsoon onset.The development of Hadley circulation at both lower and upper levels and onset of summer monsoon in Arabian Sea are of great influence in the onset of rainy season of India,while the sea-sonal reversal at lower levels barely has contributions.