冬季北大西洋涛动对热带印度洋海表热通量的影响

利用1979—2017年TropFlux海气热通量资料、ERA5再分析资料及HadISST资料，分析了冬季北大西洋涛动(North Atlantic Oscillation, NAO)与同期热带印度洋海气热通量的关系。结果表明，NAO指数与热带印度洋海气净热通量整体上呈负相关，意味着NAO为正位相时，海洋向大气输送热量，其显著区域主要位于热带西印度洋(50°～70°E,10°S～10°N)。净热通量的变化主要依赖于潜热通量和短波辐射的变化；潜热通量和短波辐射在NAO正(负)位相事件期间的贡献率分别为72.96%和61.48%(71.72%和57.06%)。NAO可通过Rossby波列影响印度洋地区局地大气环流，进而影响海气热通量；当NAO为正位相时，波列沿中低纬路径传播至印度洋地区，在阿拉伯海北部对流层高层触发异常反气旋环流。该异常反气旋性环流加强了阿拉伯高压，使得北印度洋偏北风及越赤道气流加强。伴随风速的加强，海面蒸发增强，同时加强的越赤道气流导致热带辐合带强度偏强，深对流加强引起对流层水汽和云量增多，进而引起海表下行短波辐射减少。

Effects of winter North Atlantic Oscillation on surface heat flux in tropical Indian Ocean

Based on TropFlux, ERA5 and HadlSST datasets from 1979 to 2017, this paper investigates the relationship between the North Atlantic Oscillation (NAO) and the sea-air heat flux in the tropical Indian Ocean in winter.Results show that the NAO index is negatively correlated with the net air-sea heat flux in the tropical Indian Ocean as a whole, which means that when NAO is in a positive phase, the ocean transfers heat to the atmosphere, and the significant region is mainly located in the tropical western Indian Ocean (10°S-10°N, 50°-70°E).The net air-sea heat flux anomalies are mainly contributed by the latent heat flux and shortwave radiation anomalies.The contribution rates of latent heat flux and shortwave radiation are 72.96% and 61.48% (71.72% and 57.06%) during the NAO positive (negative) phase events, respectively.NAO can affect the local atmospheric circulation in the Indian Ocean through Rossby wave train, and then affect the air-sea heat fluxes.When NAO is in a positive phase, the wave train propagates to the Indian Ocean along the mid- and low-latitude path, triggering an anomalous anticyclone circulation in the upper troposphere over the northern Arabian Sea.The anomalous anticyclone circulation enhances the Arabian high, which strengthens the northerly winds in the northern Indian Ocean and the cross-equatorial flow.With the increase of wind speed, the sea surface evaporation is enhanced.At the same time, the enhanced cross-equatorial flow leads to the stronger tropical convergence zone.The strengthening of deep convection leads to the increase of tropospheric water vapor and cloud cover, which further causes the decrease of downward shortware radiation.