夏季北印度洋海温异常对西北太平洋低层反气旋异常的影响

Impact of North Indian Ocean SSTA on Northwest Pacific Lower Layer Anomalous Anticyclone in Summer

采用1957—2002年850 hPa风场的ERA-40再分析资料,分析得知西北太平洋低层环流存在着明显的年际变化。这种年际变化表征了西北太平洋夏季风的年际变化,并且会影响东亚夏季风的变化。用Hadley海表面气压以及海表温度资料诊断得到,这种夏季西北太平洋反气旋异常(WPAC,northwest Pacific anomalous anticyclone)的年际变化与北印度洋同期海表温度变化存在很好的相关。用偏相关方法消除N ino3.4信号的同期线性影响,这种同期相关更加显著,而西南热带印度洋的同期海温与WPAC的相关并不显著。数值试验结果表明,北印度洋存在正海温异常时,北印度洋降水偏多,同时伴随着西北太平洋反气旋异常。当只有西南热带印度洋有正海温异常时,北印度洋会出现东风异常且降水减少,而西北太平洋有弱的气旋异常。数值模式结果与观测数据的诊断结果相吻合,说明当夏季北印度洋海表温度为正异常时,可能会产生西北太平洋反气旋异常。

The 850 hPa wind field of ERA-40 reanalysis data from 1957 to 2002 is analyzed, showing that the lower level circulation in the northwest Pacific has an obvious interannual variability. This variability can represent the interannual variation of summer monsoon in the northwest Pacific, and impact on East Asia summer monsoon. Based on the observed Hadley SLP and SST data, diagnosis result shows that interannual variation of the northwest Pacific anomalous anticyclone （WPAC） has a good relation with sea surface temperature in North Indian Ocean in summer. And the relation becomes more obvious when deleting the linear Nino3.4 signal by the partial correlation method. On the other hand, the northwest Pacific anomalous anticyclone has not an obvious correlation with sea surface temperature in the southwest Indian Ocean in summer. The AGCM experiments demonstrate that there is a positive precipitation anomaly over north Indian Ocean when the north Indian Ocean SST is higher with a lower level anticyclone anomaly over the northwest Pacific. When the southwest tropical Indian Ocean is warmer,there are negative precipitation anomalies and anomalous easterlies over north Indian Ocean, and there is a weak anomalous cyclone over the northwest Pacific. The numerical experiment result tallies with the observations, indicating that the warmer summer SST in north Indian Ocean will lead to the lower level anomalous anticyclone in the northwest Pacific.