降水对热带海表温度异常的邻域响应　I．数值模拟

Neighbourhood Response of Rainfall to Tropical Sea Surface Temperature Anomalies Part I: Numerical Experiment

基于低阶大气环流谱模式，本文设计了太平洋及印度洋４个不同海域的海表温度异常试验，去研究大气环流及降水对热带海表温度异常强迫作用的“同时”性响应。结果表明尽管暖性的海表温度异常均激发出低空辐合及高空辐散，但在不同海域所激发的异常流场却差异甚大。不过降水异常均发生在海表温度异常区及其毗邻处。它在对称的ＳＳＴＡ区的分布一般是非对称的。对水汽收支的分解分析表明，海表温度异常区异常降水的大小主要由异常的低空辐合决定，而异常降水的分布形态则由异常的水汽平流过程所决定。由于异常的低空辐合及异常的水汽平流过程主要发生在海表温度异常区及毗邻处，因此，降水对热带海表温度异常的响应基本Ｌ是一种邻域响应。它发生在气候平均低空气流沿海表温度异常的下风方向，或在海表温度异常所激发的低空异常气流沿气候平均海温降低的方向。

Numerical experiments of SST anomalies at different regains of indian Ocean and Pacific Ocean based on the GFDL R-15 model were designed to verify the sensitivity of atmospheric rainfall in response to tropical SST anomalies. Results show that, although tropical warm SST anomalies unexceptionally generate low-layer convergence and high-layer divergence in the troposphere, the associated streamfunction fields present remarkable differences if SST anomalies appear in.different ocean regions. In all cases, however, rainfall anomaly occurs only in the region of SST anomaly and its surroundings.Split analysis of water budget shows that, the magnitude of rainfall is mainly determined by anomalous convergence of low-layer flow, whereas the distribution of rainfall is determined by anomalous convergence of water flux. The anomalous convergences of low-layer flow and water flux in response to a given SST anomaly both occur in the region of SST anomaly and its surrouundings. The response of atmospheric rainfall to SST anomaly is thus a kind of neighbourhood response. It happens in the region where the climate mean low-layer flow is down the gradient of SST anomaly, or the anomalous low-layer flow induced by SST anomaly is down the gradient of the climate mean SST.