Abrupt rainfall transitions over the Greater Horn of Africa: Observations and regional model simulations
Abrupt rainfall transitions over the Greater Horn of Africa: Observations and regional model simulations
复制标题
大非洲之角的突然降雨转变：观测和区域模型模拟
DOI：
10.1029/2007jd009202
复制
发表时间：
2008
影响因子：
--
通讯作者：
K. Cook
中科院分区：
文献类型：
--
作者：
E. Riddle;K. Cook
[1]我们研究了大非洲之角（GHA）北部春季和夏季雨季期间大约20°纬度的季风跳跃的年度发生。这种跳跃是在一个简单的模型，在该地区的一个平滑变化的ITCZ相比。在四月和五月期间，在三个降水数据集和使用PSU/NCAR中尺度模式（MM 5）的区域气候模式模拟中，每年都观察到降雨跳变。MM 5模拟表明，降雨跃变大致与索马里急流在4月、5月和6月发展时发生的环流突变一致。特别是，索马里急流的跨赤道（赤道）分支于4月沿着东非海岸形成，将湿气（和降雨）向北带到埃塞俄比亚高原的南坡。这个纬向分支在急流的北方纬向分支之前形成，它将水汽从埃塞俄比亚南部向东转移，并为印度季风提供食物。这些结果建立了一个框架，了解降水周期的GHA，并提供了一个基础，改善亚季节预测干旱易发地区的东非。
[1] We examine the yearly occurrence of a monsoon jump of approximately 20° latitude during the boreal spring and summer rainy seasons over the Greater Horn of Africa (GHA). This jump is in contrast with a simple model of a smoothly varying ITCZ over the region. The rainfall jump is observed annually during April and May in three precipitation data sets and in regional climate model simulations using the PSU/NCAR Mesoscale Model (MM5). The MM5 simulations show the rainfall jump to be roughly coincident with abrupt circulation changes that occur as the Somali jet develops during April, May, and June. In particular, the cross-equatorial (meridional) branch of the Somali jet forms along the East African coast in April, bringing moisture (and rainfall) northward to the southern slopes of the Ethiopian plateau. This meridional branch forms well before the northern zonal branch of the jet, which diverts moisture eastward from southern Ethiopia and feeds the Indian monsoon. These results establish a framework for understanding the precipitation cycle over the GHA, and provide a foundation for improving subseasonal forecasts over drought-prone regions of eastern Africa.