Relations Among Duration of the El Niño Events, Tropical Atlantic Conditions and Rainfall Over Ceará

Abstract This paper investigates how El Niño events of different durations affect the atmospheric circulation over the Tropical North Atlantic (TNA) region, what are the consequences of these alterations in the sea surface temperature (SST) interannual variability and what are the responses, in terms of precipitation anomalies, over Ceará. Composite analyses of oceanographic and atmospheric variables were made for 18 El Niño years, divided between events of short and long duration. Events that lasted longer resulted in positive SST anomalies in the TNA region, leading to an interhemispheric gradient of SST anomalies in the Tropical Atlantic and below normal precipitation anomalies over Ceará. On the other hand, the alterations in the atmospheric circulation on TNA, during years of short duration El Niño, have not shown to be as intense as those in years of long duration El Niño. This resulted in SST anomalies on TNA close to zero and consequently, the interhemispheric gradient of SST anomalies was not observed. The near normal precipitation anomalies composites are consistent with the no formation of a SST anomalies gradient.

摘要 本文旨在研究不同持续时长的厄尔尼诺（El Niño）事件对热带北大西洋（Tropical North Atlantic, TNA）区域大气环流的影响，解析此类环流改变对海表温度（sea surface temperature, SST）年际变率的作用效应，并探讨塞阿拉（Ceará）地区在降水异常方面的响应特征。研究基于18个厄尔尼诺年的海洋与大气变量开展合成分析，将事件划分为短持续时长与长持续时长两类。持续时长更长的厄尔尼诺事件会引发热带北大西洋区域出现正海表温度异常，进而形成热带大西洋海表温度异常的半球间梯度，并导致塞阿拉地区产生低于常年的降水异常。与之相对，在短持续时长厄尔尼诺年期间，热带北大西洋区域的大气环流变化并未呈现出与长持续时长厄尔尼诺年相当的强度。这使得热带北大西洋的海表温度异常接近零值，因此未观测到海表温度异常的半球间梯度。接近常年的降水异常合成结果与海表温度异常梯度未形成的情形相一致。