海南岛秋季降水异常对应的热带大尺度环流和海温

海南岛的地理环境特殊,具有独特的降水变化特征.作者利用海南岛7个站的月降水资料、NCEP再分析资料及NOAA的海温资料,研究了近45年海南岛降水的变化规律,并给出了产生降水异常的一个可能的物理机制.结果表明,海南岛降水具有明显的季节变化,一年中秋季的9、10月份降水最大,而且这两个月降水的年际方差占全年降水总方差的47.1%.秋季降水的年际异常对应的环流形式主要表现为对流层中下层存在的两个异常的气旋和反气旋中心.当降水偏多时,有两支异常的气流分别从热带太平洋和印度洋吹向海南岛附近地区,为该地区提供了更多的水汽,有利于岛上降水.而当降水偏少时,两支异常的气流变为从大陆吹向海洋,使海南岛上空水汽偏少,不利于岛上降水.另一方面,这种与秋季降水异常对应的环流异常是由赤道中东太平洋海表温度异常造成的,异常的海温将使热带地区的沃克环流发生异常,并最终使海南岛附近环流发生异常,导致降水异常.

Tropical Large-Scale Atmospheric Circulation and Sea Surface Temperature Corresponding to Autumn Precipitation in Hainan Island

The statistic characteristics as well as the forming mechanics of precipitation in Hainan Island are investigated by using the latest 45-year monthly rainfall data at 7 stations over the Hainan region,NCEP data and SST data.The results show that the seasonal change of precipitation is very obvious to all stations in Hainan Island.The precipitation between May and August covers about 80 percent of total.The maximal value appears in September and October and the minimal value appears in January every year.The maximal interannual variability of precipitation is also found in September and October.Meanwhile,the spatial distribution of precipitation is severely asymmetric and the highest precipitation occurs in the eastern and central region where the precipitation is two times larger than that of the western region.The terrain is an important factor,which makes the spatial distribution of precipitation much complicated.Abnormal autumn precipitation in Hainan Island corresponds to abnormal atmospheric general circulation in the middle-low troposphere.There is an abnormal cyclone which is located in the Indo-China peninsula and an abnormal anticyclone which lies in the east of Taiwan when precipitation is more than normal.An abnormal eastward airflow which comes from the Indian Ocean and another westward airflow which comes from the tropical Pacific converge in South China Sea and go forward to northwest.The two airflows supply plentiful water vapor which contributes to rainfall.An inverse circulation sense is observed when precipitation is less than normal.Based on the correlation and composite analysis,the possible influence of the sea surface temperature(SST) in the equatorial central-eastern Pacific on autumn precipitation in Hainan Island is revealed.Abnormal SST leads to abnormal precipitation in Hainan Island by modifying the Walker circulation.When negative (positive) SST anomalies appear,the Walker circulation is stronger(weaker) than normal.The enhanced(weakened) Walker circulation leads to the abnormal eastward(westward) airflow in the Indian Ocean and the abnormal westward(eastward) airflow in the tropical pacific.