ABSTRACT: The sensitivity of tropical rainfall to sea surface temperature (SST) fluctuations was investigated using a multi-scale analysis framework, covering time scales between a few days and 1 decade. The analysis includes an intercomparison between a satellite-based observational dataset and two twentieth century general circulation model (GCM)-based products: the ERA-20CM ensemble of atmospheric simulations and the ERA-20C reanalysis. The results provide robust evidence for the physical linear response of regional rainfall to SST fluctuations at multi-year time scales. All datasets showed tight correlations between rainfall and local SST, the Niño 3.4 index and local surface downwelling longwave radiation (DLR) over wide tropical regions. Additionally, the rainfall-DLR correlation held under a clear sky approximation. These 3 correlations are tightly related since the Niño 3.4 index and clear sky DLR can be computed from SST alone. The latter requires a robust correlation between local precipitable water vapor (W) and SST (i.e. Clausius-Clapeyron relationship), which was confirmed at multi-year scales over large portions of the tropics. All datasets also showed a robust transition in all these correlations at faster time scales (below ~1 yr), suggesting a change in the physical mechanisms controlling rainfall (and W) variability. Based on the linear sensitivities, 3 simplified models were proposed to reconstruct 3-yearly tropical rainfall time series at 5° resolution, forced only by ERA-20CM’s prescribed SST fields. The simplified linear response models were shown to reproduce observations with similar accuracy to GCM-based products, despite having a (easily correctable) systematic bias. The good agreement between all datasets, including the simplified model, provides confidence to the representation of the tropical rainfall response to SST fluctuations in GCM-based and satellite-based products, at least at multi-year time scales.

中文翻译：

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热带降雨对海表温度波动的多尺度结构

摘要：使用多尺度分析框架研究了热带降雨对海表温度（SST）波动的敏感性，涵盖了从几天到十年的时间尺度。该分析包括基于卫星的观测数据集和两种基于20世纪通用循环模型（GCM）的产品之间的比较：大气模拟的ERA-20CM集合和ERA-20C重新分析。研究结果为多年降雨条件下区域降雨对海表温度波动的物理线性响应提供了有力的证据。所有数据集都表明，在热带地区，降雨与当地SST，Niño3.4指数和当地地面下行长波辐射（DLR）之间存在紧密的相关性。另外，降雨-DLR相关性保持在晴朗的天空近似下。这3个相关性密切相关，因为Niño3.4指数和晴朗的天空DLR可以仅通过SST计算得出。后者需要局部可沉淀水蒸气之间的稳健相关性（W）和SST（即Clausius-Clapeyron关系），这在热带的大部分地区都在多年尺度上得到了证实。所有数据集还显示出所有这些相关性在较快的时间尺度（〜1年以下）上均呈现出稳健的过渡，表明控制降雨（和W） 变化性。基于线性敏感性，提出了3个简化模型，以仅在ERA-20CM规定的SST场的推动下，以5°分辨率重建3年热带降雨时间序列。尽管具有（易于校正）系统偏差，但简化的线性响应模型显示出可再现与基于GCM的产品相似的精度的观察结果。包括简化模型在内的所有数据集之间的良好一致性，至少在多年的时间尺度上，对基于GCM和基于卫星的产品中SST波动对热带降雨响应的表示提供了信心。