A Possible Influence of Equatorial Winds on the September 2002 Southern Hemisphere Sudden Warming Event
A Possible Influence of Equatorial Winds on the September 2002 Southern Hemisphere Sudden Warming Event
复制标题
赤道风对2002年9月南半球突然变暖事件的可能影响
DOI：
10.1175/jas-3339.1
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发表时间：
2005
影响因子：
3.1
通讯作者：
A. Charlton
中科院分区：
文献类型：
--
作者：
L. Gray;W. Norton;C. Pascoe;A. Charlton
2002年9月南半球平流层突然变暖是出乎意料的，原因有二。首先，南半球的行星波活动非常微弱，而且从未观测到仲冬变暖，至少在平流层上部的观测定期可用之后没有。其次，暖化发生在平流层下部准两年振荡（QBO）的西位相。这是出乎意料的，因为变暖通常被认为是更有可能在东相的QBO，当零风线存在于冬季亚热带，因此限制行星波传播到更高的纬度接近极涡。首先，这些证据表明，突然变暖因此必须是一个简单的结果，强烈的行星波强迫对流层。然而，最近的模式研究表明，隆冬极涡也可能是敏感的赤道风在平流层上部，该地区占主导地位的半年振荡。本文对ECMWF再分析（ERA）和气象局同化资料两种不同资料源的赤道纬向风时间序列进行了回顾。两者都表明2002年平流层上部10 hPa以上的赤道风是偏东的。理想化的模型实验中，模拟的赤道风放松对这些意见，为不同的年份，以研究是否异常东风在2002年可能会影响变暖事件的时间。结果发现，2002年赤道风加快了模式中一个变暖事件的演变。因此，本研究认为，异常东风在1-10-hPa区域可能是一个贡献的因素，在观测到的上海变暖的发展。然而，它的结论是，这是不可能的，单独的异常赤道风可以解释2002年的变暖事件。
The stratospheric sudden warming in the Southern Hemisphere (SH) in September 2002 was unexpected for two reasons. First, planetary wave activity in the Southern Hemisphere is very weak, and midwinter warmings have never been observed, at least not since observations of the upper stratosphere became regularly available. Second, the warming occurred in a west phase of the quasi-biennial oscillation (QBO) in the lower stratosphere. This is unexpected because warmings are usually considered to be more likely in the east phase of the QBO, when a zero wind line is present in the winter subtropics and hence confines planetary wave propagation to higher latitudes closer to the polar vortex. At first, this evidence suggests that the sudden warming must therefore be simply a result of anomalously strong planetary wave forcing from the troposphere. However, recent model studies have suggested that the midwinter polar vortex may also be sensitive to the equatorial winds in the upper stratosphere, the region dominated by the semiannual oscillation. In this paper, the time series of equatorial zonal winds from two different data sources, the 40-yr ECMWF Re-Analysis (ERA) and the Met Office assimilated dataset, are reviewed. Both suggest that the equatorial winds in the upper stratosphere above 10 hPa were anomalously easterly in 2002. Idealized model experiments are described in which the modeled equatorial winds were relaxed toward these observations for various years to examine whether the anomalous easterlies in 2002 could influence the timing of a warming event. It is found that the 2002 equatorial winds speed up the evolution of a warming event in the model. Therefore, this study suggests that the anomalous easterlies in the 1–10-hPa region may have been a contributory factor in the development of the observed SH warming. However, it is concluded that it is unlikely that the anomalous equatorial winds alone can explain the 2002 warming event.