西太平洋暖池海温异常年夏季东亚大气环流特征

利用NCEP/NCAR逐月再分析资料对西太平洋暖池区海表水温冷、暖异常年夏季东亚大气环流作了合成分析,与气候平均比较后发现:夏季暖池区暖异常时,在西太平洋上空的对流层低层产生一个强的反气旋偏差环流,因而不利于南海南部和赤道太平洋地区的西风发展,使热带夏季风强度减弱;在南海西部和中南半岛东部有偏差气流转向大陆,因而增强了偏南风,使副热带夏季风强度增强;在对流层中、下层副高脊线位置偏南,大约以400hPa为分界线,低层副高强度增强,高层副高强度减弱。西太平洋暖池冷异常年夏季东亚大气环流特征大致与上述情况相反,且强度或变化幅度小于暖异常年夏季。另外,与气候平均比较,暖异常年纬向Walker环流上升支大幅西移,而冷异常年该环流上升支则东移。

Characteristic analysis of East Asia atmospheric circulation in summers of abnormal years of the Western Pacific Warm Pool

Based on NCEP/NCAR reanalyzed data, a composite analysis of East Asia atmospheric circulation in summer of SST abnormity years of the Western Pacific Warm Pool is made. In comparison with the average conditions in climate, the results show that when the Warm Pool SST is positive, a strong anticyclone deviation circulation occurs in the lower troposphere over the Western Pacific Ocean along with positive SST anomalies of the Warm Pool, going against development of the westerly over the south of the South China Sea and the equatorial Pacific Ocean, and weakening the intensity of tropical summer monsoon; a deviation flow over the area between the west of the South China Sea and the eastern part of the Indo-China peninsula turns to the China's mainland, the southerly boosting up and the subtropical summer monsoon becoming stronger; in the middle and lower troposphere, the position of the ridge line of the west Pacific subtropical high goes southward, and bounded approximately by 400 hPa, the intensity of subtropical high strengthens in the lower troposphere and weakens in the upper troposphere. When the Warm Pool SST is negative, the situations are basically opposite to the above, the intensity or variation extent is smaller than that in the warm abnormal years. In addition, the ascending branch of the Walker circulation moves westward largely in the warm abnormal years, but shift eastward in the cold abnormal years.