Teleconnections between the tropical Pacific and the Sahel
Teleconnections between the tropical Pacific and the Sahel
复制标题
DOI：
10.1002/qj.49712757512
复制
发表时间：
2001-07-01
影响因子：
8.9
通讯作者：
Rowell, DP
中科院分区：
文献类型：
--
作者：
Rowell, DP
更好地了解赤道遥相关是研究热带地区季节预测和未来气候变化的一个关键方面。本文利用观测数据和模式数据相结合的方法，探讨了太平洋海温异常对半干旱萨赫勒地区降水波动的影响。这项研究的第一个关键议题是确定太平洋海温异常变化与萨赫勒地区联系最密切的那些方面。其中一个类似于太平洋中部和东部的经典厄尔尼诺南方涛动模式，在厄尔尼诺阶段增加了萨赫勒干旱的可能性，早期研究也阐明了这一点。这里表明，虽然这种联系的一部分是间接的(通过大西洋SST进行操作)，但其主要影响似乎是通过直接的大气遥相关。另一个同样重要的关键模式是从西太平洋到西印度洋的海温的大尺度纬向梯度，这是一种新的分析技术揭示的。如果被削弱，这也会增加萨赫勒干旱的可能性。用观测到的或理想的海温强迫的大气环流模式试验证实了这两种对萨赫勒的影响。至关重要的是，当两者都存在时，它们在萨赫勒地区的影响大大加强，此外，进一步的经验分析表明，它们在很大程度上是独立的。第二个关键主题是对这种太平洋-萨赫勒远程联系的机制的调查。这些似乎涉及异常的静止赤道波，在向东和向西的方向上都发生了通信。在厄尔尼诺年，东太平洋对流加热异常产生的开尔文波横跨大西洋，印度洋对流加热异常响应西太平洋-印度洋海温梯度异常，在印度洋上空出现赤道Rossby波。它们在非洲上空相互作用，加强了萨赫勒地区的大规模下沉，从而减少了季节性降雨量。赤道波传播的年际变化或亚季节制度的驻留似乎没有起到实质性的作用。
A greater understanding of equatorial teleconnections is a key aspect of research into seasonal prediction and future climate change for tropical regions. Here the impact of Pacific sea surface temperature (SST) anomalies on rainfall fluctuations over the semi-arid Sahel is explored, using a combination of observed and model data.The first key topic of this study is the identification of those aspects of anomalous Pacific SST variability that are most strongly linked to the Sahel. One of these, also illuminated by earlier studies, is similar to the classic El Nino Southern Oscillation pattern in the central and east Pacific, which in its El Nino phase increases the likelihood of Sahel drought. It is shown here that, although a part of this link is indirect (operating via Atlantic SSTs), its main effect appears to be through a direct atmospheric teleconnection. The other critical pattern, of equal importance and revealed here by a novel analysis technique, is the large-scale zonal gradient of SSTs from the west Pacific to the cast Indian Ocean. If weakened, this too enhances the likelihood of Sahel drought. Atmospheric general circulation model experiments, forced either by observed or idealized SSTs, are used to confirm these two influences on the Sahel. Crucially, their Sahelian impact is substantially reinforced when both are present and, additionally, further empirical analysis shows them to be largely independent.The second key topic is an investigation of the mechanisms for this Pacific-Sahel teleconnection. These appear to involve anomalous stationary equatorial waves, with communication occurring in both the eastward and westward directions. In El Nino years (for example), a Kelvin wave emanates across the Atlantic from east Pacific convective heating anomalies, and an equatorial Rossby wave appears over the Indian Ocean in response to the anomalous west Pacific-Indian Ocean SST gradients via convective heating anomalies over the Indian Ocean. These interact over Africa to enhance large-scale subsidence over the Sahel, thus reducing seasonal rainfall totals. Interannual changes in propagating equatorial waves or in the residence of subseasonal regimes appear not to play a substantial role.