The onset and cessation of seasonal rainfall over Africa
The onset and cessation of seasonal rainfall over Africa
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DOI：
10.1002/2016jd025428
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发表时间：
2016-10-01
影响因子：
4.4
通讯作者：
Allan, Richard P.
中科院分区：
文献类型：
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作者：
Dunning, Caroline M.;Black, Emily C. L.;Allan, Richard P.
非洲降雨季节周期的变化对农业至关重要。在这里，确定发病和停止时间的客观方法首次扩展到整个非洲。该方法适用于五个观测数据集和 ERA-中期再分析。与已知的非洲降雨物理驱动因素的兼容性、与本土方法的一致性以及基于卫星的降雨数据集之间的普遍一致性证实该方法正在捕获非洲降雨的正确季节性进展。加纳和科特迪瓦沿海地区的一年两次降雨情况得到了正确识别。然而，ERA-Interim 再分析在有两个雨季的地区表现出时间偏差，并且 ERA-Interim 和 ARCv2 观测数据集在西非表现出一些不一致的偏差。该方法可用于分析季节-年际变化和长期变化。在东非，我们发现降雨中断和随后的人道主义灾难与雨季较短和较弱有关，例如，2011年长雨平均缩短了11天。该地区短雨的停止在厄尔尼诺现象中晚了7天，在拉尼娜现象中提前了5天，而开始日期只有很小的变化。本文描述的方法适用于多个数据集和大区域，包括经历多个雨季的区域。因此，它为调查整个非洲季节周期的变率和变化提供了一种手段。 要点 使用适应方法产生的非洲雨季开始/结束的诊断模式与物理驱动因素兼容 基于卫星的降雨数据中一致的开始/结束特征，ERA-中期缺乏两年一次的制度 非洲之角的雨季结束在厄尔尼诺年晚 7 天，在拉尼娜年早 5 天
Variation in the seasonal cycle of African rainfall is of key importance for agriculture. Here an objective method of determining the timing of onset and cessation is, for the first time, extended to the whole of Africa. The method is applied to five observational data sets and the ERA-Interim reanalysis. Compatibility with known physical drivers of African rainfall, consistency with indigenous methods, and generally strong agreement between satellite-based rainfall data sets confirm that the method is capturing the correct seasonal progression of African rainfall. The biannual rainfall regime is correctly identified over the coastal region of Ghana and the Ivory Coast. However, the ERA-Interim reanalysis exhibits timing biases over areas with two rainy seasons, and both ERA-Interim and the ARCv2 observational data set exhibit some inconsistent deviations over West Africa. The method can be used to analyze both seasonal-interannual variability and long-term change. Over East Africa, we find that failure of the rains and subsequent humanitarian disaster is associated with shorter as well as weaker rainy seasons, e.g., on average the long rains were 11days shorter in 2011. Cessation of the short rains over this region is 7days later in El Nino and 5days earlier in La Ninayears with only a small change in onset date. The methodology described in this paper is applicable to multiple data sets and to large regions, including those that experience multiple rainy seasons. As such, it provides a means for investigating variability and change in the seasonal cycle over the whole of Africa.Key PointsDiagnosed patterns in onset/cessation of African rainy seasons, produced using an adapted method, are compatible with physical drivers Consistent onset/cessation characteristics in satellite-based rainfall data, ERA-Interim deficient for biannual regime Rainy season cessation over the Horn of Africa is 7days later in El Ninoyears and 5days earlier in La Nina