高低层纬向风切变的年际变率及气候学意义

用1959～1998共40年全球格点风场资料计算了200 hPa与850 hPa的纬向风速差, 即对流层纬向风切变(简称TZWS),并在此基础上得到其距平值。为了全面考察对流层中环流异常的年际变率特征, 根据TZWS的标准差分布, 文中选出了7个TZWS标准差数值大于5 m/s的代表性区域。这7个区域分别位于赤道中太平洋、赤道东太平洋、北太平洋亚热带地区、南太平洋亚热带地区、赤道大西洋、亚洲西南部以及东北部。前5个分别位于赤道、亚热带太平洋和大西洋的区域TZWS指数, 其年际变率与ENSO循环有密切联系, 反映了热带海洋温度异常对低纬度地区对流层环流的影响; 后2个区域的TZWS指数反映的是亚洲西南部和东北部的气候统变率, 在年际时间尺度上与ENSO循环有着明显的区别。通过对全球陆地降水和温度场的分析, 比较了热带、副热带的TZWS指数以及北极涛动指数的异同, 发现后2个区域TZWS指数能很好且能独立反映出北半球中高纬度地区陆地降水及陆地温度的异常模态。

Interannual Variability and Climatological Significance of Zonal Wind Shear between 200 hPa and 850 hPa

The monthly values of the zonal wind vertical difference or zonal wind shear(ZWS) between 200 hPa and 850 hPa are used to assess the interannual variability of the tropospheric circulation anomalies.Seven regional indices of ZWS with the standard deviation more than 5 m/s are constructed.These regions are located in the central equatorial Pacific,the eastern equatorial Pacific,the northern and southern subtropical Pacific,the equatorial Atlantic,subtropical Arabia and Northeast Asia.The interannual variability of ZWS indices in the first five regions in the equatorial-subtropical Pacific and equatorial Atlantic are closely correlated with the ENSO cycle,which reflects the impact of tropical ocean temperature anomaly on the tropospheric circulation in lower latitudes.The last two ZWA indices,which are the signals of the climate variation over South Asia and Northeast Asia,differ significantly from the ENSO index on the interannual timescale.By analyzing the global land precipitation and temperature fields and comparing the tropical and subtropical ZWS indices with the AO index,the last two ZWS indices can well represent anomalous mode of land precipitation and temperature fields in the middle and high latitudes.