El Niño调控太平洋–南美型遥相关的动力机制研究

Dynamical Mechanisms of El Niño Modulating the Pacific-South American Teleconnection

摘要: 本文基于1950~2024年NCEP-NCAR再分析资料，研究了El Niño背景下太平洋–南美型(PSA)正事件的时空特征与动力机制。PSA被定义为南太平洋(20˚~70˚S, 150˚E~70˚W) 500 hPa位势高度EOF第一模态，以季节内振荡为主导，年际尺度存在4.8年周期。信息流分析证实ENSO对PSA具有显著因果强迫作用。El Niño背景下PSA正事件呈准正压结构，最强中心位于250 hPa。动力机制分析表明，El Niño引起热带对流异常，使澳大利亚东北部至新西兰一带成为有效Rossby波源区。波射线通量诊断揭示，源自热带的Rossby波能量主要沿副热带急流传播，仅少部分抵达新西兰后发生折射转向高纬度PSA中心；抵达新西兰的波能可激发次级波源，其激发的Rossby波高效向PSA中心传播，形成“接力”效应。本研究揭示了El Niño调控PSA的波动力学机制，发现新西兰是关键的波能中转站。

Abstract: Based on NCEP-NCAR reanalysis data from 1950 to 2024, this study investigates the spatiotemporal characteristics and dynamical mechanisms of positive Pacific-South American (PSA) events under El Niño background. The PSA is defined as the first EOF mode of 500 hPa geopotential height anomalies over the South Pacific (20˚~70˚S, 150˚E~70˚W). It is dominated by intraseasonal oscillations and exhibits a significant 4.8-year period on interannual timescales. Information flow analysis confirms the causal forcing of ENSO on the PSA. Positive PSA events under El Niño background show a quasi-barotropic structure, with the strongest center near 250 hPa. Dynamical analysis reveals that anomalous tropical convection induced by El Niño makes the region from northeastern Australia to New Zealand an effective Rossby wave source. Wave ray flux diagnosis indicates that Rossby wave energy from the tropics propagates mainly along the subtropical jet stream. Only a small portion reaches New Zealand, where it refracts toward the high-latitude PSA center. More importantly, wave energy arriving near New Zealand can excite secondary wave sources, whose excited Rossby waves propagate efficiently to the PSA center, forming a “relay” effect. This study reveals the wave dynamics mechanism of El Niño modulating the PSA and identifies New Zealand as a key wave energy transfer station.