Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA.
Nature. 2013 Jan 17;493(7432):389-92. doi: 10.1038/nature11785.
The recent decades-long decline in East African rainfall suggests that multidecadal variability is an important component of the climate of this vulnerable region. Prior work based on analysing the instrumental record implicates both Indian and Pacific ocean sea surface temperatures (SSTs) as possible drivers of East African multidecadal climate variability, but the short length of the instrumental record precludes a full elucidation of the underlying physical mechanisms. Here we show that on timescales beyond the decadal, the Indian Ocean drives East African rainfall variability by altering the local Walker circulation, whereas the influence of the Pacific Ocean is minimal. Our results, based on proxy indicators of relative moisture balance for the past millennium paired with long control simulations from coupled climate models, reveal that moist conditions in coastal East Africa are associated with cool SSTs (and related descending circulation) in the eastern Indian Ocean and ascending circulation over East Africa. The most prominent event identified in the proxy record--a coastal pluvial from 1680 to 1765--occurred when Indo-Pacific warm pool SSTs reached their minimum values of the past millennium. Taken together, the proxy and model evidence suggests that Indian Ocean SSTs are the primary influence on East African rainfall over multidecadal and perhaps longer timescales.
近几十年来，东非地区的降雨量一直在减少，这表明多年代际变化是该脆弱地区气候的一个重要组成部分。先前基于分析仪器记录的研究表明，印度和太平洋海洋表面温度（SST）可能是东非多年代际气候变化的驱动因素，但仪器记录的长度很短，无法完全阐明潜在的物理机制。在这里，我们表明，在超过十年的时间尺度上，印度洋通过改变当地的沃克环流来驱动东非的降雨变化，而太平洋的影响则很小。我们的研究结果基于过去一千年的相对湿度平衡的代理指标，并结合耦合气候模型的长期控制模拟，表明东非沿海地区的潮湿条件与印度洋东部的冷 SST（和相关的下降环流）以及东非上空的上升环流有关。在代理记录中确定的最显著事件——1680 年至 1765 年的沿海降雨——发生在印度-太平洋暖池 SST 达到过去千年最低值的时候。综合代理和模型证据表明，印度洋 SST 是影响东非降雨的主要因素，这种影响可能跨越多年代际甚至更长时间。
