两种形态ENSO对南半球热带外气候变化特征的影响

本研究利用1979—2012年欧洲中期天气预报中心(ECMWF)的ORAP5(Ocean Reanalysis Pilot 5)海洋/海冰再分析资料和ERA-Interim气象再分析资料,采用回归分析方法,分1979—1998年和1999—2012年两个时间段探讨了南半球热带外地区气候变化对两种不同形态ENSO的响应特征。结果表明,南半球热带外区域气候在1999年前后两个时段对ENSO的响应表现出了较大的年代际变化特征。1979—1998年南半球热带外气候变量对Nio3指数在时间上的相关性和空间上的响应强度都普遍大于Nio4指数,说明这一时段东部型ENSO对南半球热带外区域气候变化的影响要更强一些。在1999—2012年,不同形态ENSO与气候变量的相关性大小并无明显的规律,而且空间响应场的差异性并不大。海平面气压、风场和气温对ENSO变化的响应在南半球冬季表现最为强烈,在夏季最弱。三者在1999—2012年秋季对Nio3指数和Nio4指数的响应场中出现了纬向三波数结构。1999—2012年冬季,有异于海平面气压和风场,在罗斯海和阿蒙森海海域海表气温对Nio4变化的正响应明显强于对Nio3的响应,该特征在混合层温度中也有体现,表明海表气温随ENSO的变化受海洋特征变化影响较大。混合层深度和混合层温度的响应场之间存在很大的相关性,混合层温度响应在秋季表现最强,春季最弱,混合层深度响应与之相反。在1979—1998年,海冰密集度对不同Nio指数变化的响应差异主要出现在海冰结冰季节,而海冰厚度对不同Nio指数变化的响应差异在夏季表现较强。海冰密集度和厚度对Nio3变化响应的年代际差异在秋冬季节更加明显,对Nio4变化响应的年代际差异在秋、冬、春季都较明显。

Impacts of two types of El Niño–Southern Oscillation events on extratropical climate of Southern Hemisphere

Impacts of eastern Pacific and central Pacific El Niño–Southern Oscillation (ENSO) events on climate changes in the extratropical area of the Southern Hemisphere were investigated for two different periods (1979–1998 and 1999–2012) and four seasons using the Ocean Reanalysis Pilot 5 (ORAP5) ocean and sea-ice reanalysis product and the ERA-Interim atmospheric reanalysis product for 1979–2012. Results show that there was significant interdecadal variability in the response patterns of climate variables to ENSO variations before and after 1999. Between 1979 and 1998, correlation between the dominant empirical orthogonal function of Southern Hemisphere extratropical climate variables and responses of the climate variables to ENSO events were both higher for the Niño3 sea surface temperature anomaly index, indicating that Eastern Pacific-type ENSO events had larger influences on Southern Hemisphere extratropical climate changes. Between 1999 and 2012, there were no considerable differences between the response fields to the variations of different Niño indices. For both periods, the atmospheric variables, including sea-level pressure, surface wind and surface air temperature, showed the strongest and weakest responses to ENSO events in winter and summer, respectively, and they manifested a zonal wavenumber-3 structure in their response fields in austral autumn. For 1999–2012, unlike responses of sea-level pressure and surface wind, responses of surface air temperature over the Ross and Amundsen Seas to variations in the Niño4 index were stronger than those to variations in the Niño3 index. This feature was also found in the response fields of mixed layer temperature, indicating the presence of oceanic influences in surface air temperature anomalies. Responses of mixed layer depth and temperature were closely related to variations in Niño indices. Between 1979 and 1998, differences in the responses of sea-ice concentration to variations in different Niño indices mainly occurred during the freezing seasons, while differences in sea-ice thickness responses to variations in different Niño indices mainly occurred in summer. Interdecadal variability in sea-ice concentration and thickness responses to variations in the Niño3 index was large in autumn and winter, while variability in responses to variations in the Niño4 index was large in all non-summer months.