华西秋雨准4年周期特征及其与赤道太平洋海表温度的关系

利用1959～2011年华西地区气象台站资料、NCEP/NCAR再分析资料、NOAA海表温度资料, 采用多锥度—奇异值分解(MTM-SVD)方法, 研究了华西秋雨的准4年周期特征及其与赤道太平洋海表温度的协同变化关系。研究结果表明:华西秋雨具有显著的准4年周期, 其典型循环表现为"偏强, 略偏强, 偏弱, 略偏弱"的特点。在准4年周期上赤道中太平洋海表温度对华西秋雨的协同变化表现为"偏低, 略偏低, 偏高, 略偏高", 这种协同变化从初夏就体现出来, 并一直持续到秋末。同时在准4年周期上, 华西秋雨对ENSO事件也存在一定的响应, 但是主要体现在发生强ENSO事件时。准4年周期的环流分析表明, 夏季到秋季赤道中太平洋海表温度偏低(高)时, 秋季500 hPa高度场出现东亚/太平洋(EAP)遥相关波列正(负)异常, 西太平洋副热带高压偏西(东), 华西地区来自南海西太平洋和孟加拉的水汽输送偏多(少), 华西秋雨偏强(弱)。

The Characteristics of Huaxi Autumn Rain and its Relationship with Sea Surface Temperatures over the Equatorial Pacific

Features of Huaxi Autumn Rain (HAR) quasi-four-year period and their relationship to Sea Surface Temperature (SSTs) over the equatorial Pacific Ocean are examined using data from meteorological stations in Huaxi, NCEP/NCAR reanalysis data, NOAA SST data and the Multi-Taper Method-Singular Value Decomposition (MTM-SVD) method. Results show that central equatorial Pacific SSTs cause a notable quasi-four-year period in the HAR, with yearly characteristics that are stronger, a bit strong, weaker, and a bit weak, during each year within the period, and SST joint features that are lower, a bit low, higher, and a bit high during each year. The signal is present from early summer until late fall. Circulation analysis indicates that the HAR is strong (weak) when the summer central equatorial Pacific SST anomaly is low (high), the 500-hPa height field anomaly is positive (negative), the west Pacific subtropical winds are westerly (easterly), and moisture transport from the south China Sea and Bay of Bengal is more (less). The HAR also responds to the El Niño-Southern Oscillation (ENSO), and is mainly evident during strong ENSO events.