热带北大西洋海温与降水关系的季节性特征及其物理机制
Seasonality of the SST-precipitation relationship over the North Tropical Atlantic and its possible mechanisms
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摘要: 资料和方法基于英国哈德莱中心提供的逐月海表温度资料、美国全球降水气候中心提供的逐月降水资料以及CMIP6历史模拟资料,目的本文探究了热带北大西洋海温异常与降水关系的季节性特征及其在有无ENSO海温强迫下的差异,并分析了可能的物理机制。结果 结论研究结果表明,热带北大西洋海温和局地降水的关系呈现出明显的季节性。在春、夏季节,该区域海温与降水呈显著正相关,局地海气耦合强;相对而言,秋、冬季节海气耦合弱,局地降水对海温异常几乎没有响应。进一步研究表明,这种季节性主要是由热带北大西洋气候态海温及局地海温变率的季节循环所导致。春季热带北大西洋气候态海温偏冷,但该季节的强海温变率使海温可突破对流阈值引发降水异常;夏季偏暖的气候态海温使得该区域海气耦合活跃;尽管秋季气候态海温也偏暖,但是减小的海温变率使得局地降水响应减弱,易受外界噪音干扰;与夏季相反,冬季偏冷的气候态海温导致该区域海气耦合较弱。由于ENSO对热带大西洋降水的影响主要位于5°N以南,因此在有无ENSO海温异常强迫下该地区海气耦合关系几乎没有差异。本文的结果强调了春、夏季节热带北大西洋海温异常在局地对流及其相关气候影响中的重要作用,这对热带北大西洋海温异常相关的短期气候预测具有重要的意义。Abstract: Based on the monthly sea surface temperature (SST) data from the Met Office Hadley Centre, the Global Precipitation Climatology Project monthly precipitation data, and the historical simulations from Coupled Model Intercomparison Project Phase 6 climate models, the present work investigates the seasonality of SST-precipitation relationship over the North Tropical Atlantic (NTA) and possible role of ENSO (El Ni?o-Southern Oscillation) in it. It is found that the relationship of SST anomalies in the NTA with local precipitation exhibits a remarkable seasonality. During spring and summer, there is a strong positive correlation between SST and precipitation in this region, indicating a strong local ocean-atmosphere coupling. In contrast, in autumn and winter, the ocean-atmosphere coupling weakens significantly, and almost no significant precipitation response to SST is detected. Further analysis reveals that this seasonality is mainly associated with the seasonal cycle of the background SST and local SST variability in the NTA. Despite cooler background SST in spring, the strong SST variability during this season makes SST easy to exceed the convection threshold and thus induce precipitation anomalies. In summer, the warm background SST favors in the enhanced local ocean-atmosphere coupling. The relatively decreased SST variability in autumn weakens the local precipitation response, despite with a relatively warm SST background. In contrast to summer, the cooler background SST in winter results in a weak ocean-atmosphere coupling. Since the impact of ENSO on tropical Atlantic precipitation is mainly located south of 5°N, there is almost no difference in the local ocean-atmosphere coupling in the tropical North Atlantic with or without ENSO SST forcing. These findings emphasize the critical role of spring and summer NTA SST anomalies in local convection and associated climate impacts, which is of significant importance for short-term climate prediction related to the NTA SST.