摘要:基于1961~2016年淮河流域172个测站逐日降水资料，分析了淮河夏季降水的多时间尺度变率，发现其具有显著的准两年周期，1990年代以来亦呈现出明显的年代际变化。EOF分析结果显示，淮河夏季降水的异常主要表现为全流域一致偏多或偏少型（第一模态），其方差贡献高达37%。相比于长江中下游地区，淮河夏季降水与东亚500 hPa位势高度场上的EAP遥相关型关系很弱，但和对流层低层西南水汽输送有更好的对应关系，表现为从索马里半岛至淮河流域的多个正负交替的相关波列。这一波列表明当索马里越赤道气流加强时，通过热带印度洋西风的纽带作用加强了进入淮河流域的西南暖湿气流，并在淮河上空低层形成水汽辐合，造成淮河多雨，反之当索马里越赤道气流强度弱时，淮河夏季降水偏少。索马里越赤道气流和中国台站降水的空间相关同样显示出最显著的相关区位于淮河流域。进一步的分析发现，研究时段内二者关系并非稳定维持，而是表现出显著的年代际变化，近二十年来索马里越赤道气流对淮河流域夏季降水的影响明显增强，且在季节预测上的指示意义也在增强。这一增强的可能原因是索马里越赤道气流与流域南侧的经向水汽输送和西侧的纬向水汽输送的关系均发生了年代际反转，并且这两条水汽输送带对流域夏季降水的影响发生了年代际增强。
关键词:索马里越赤道气流/
淮河流域/
夏季降水/
年代际
Abstract:Multi-time-scale variations of summertime precipitation in Huaihe River basin during 1961-2016 are analyzed based on daily precipitation observed at 172 meteorological stations. Results reveal a significant quasi-biennial cycle in the entire study period and a decadal cycle since the 1990s. EOF analysis shows that the anomalies of summer precipitation in the basin are mainly represented by a uniformly more or less anomaly mode in the whole basin (the first leading mode), which explains about 37% of the total variance. Compared with precipitation in the middle and lower reaches of the Yangtze River, precipitation in Huaihe River basin has a poor relationship with the EAP teleconnection of 500 hPa geopotential height in East Asia, but has a much more significant relationship with the water vapor transport of southwesterly summer monsoon in the lower troposphere. Their correlation field displays an alternating positive-negative correlation wave trains from Somali Peninsula to Huaihe River basin. The wave trains indicate that when the Somalia cross-equatorial flow (SCEF) strengthens, the southwesterly moisture transport into Huaihe River basin increases due to the effects of the westerly winds over the tropical India Ocean, leading to water vapor convergence over Huaihe River basin in the lower troposphere and abnormally wet or flood climate there. On the contrary, dry or drought climate would occur when the SCEF is weak. The spatial correlation field between the SCEF and precipitation in China also shows that the most significant correlation region is located in Huaihe River basin. However, during the study period of this paper, the above relationship is not stable and exhibits an obvious interdecadal enhancement, indicating that the impact of the SCEF on summer precipitation in the basin has significantly enhanced in the recent two decades. This enhancement may be related to the changed relationships between the SCEF and the meridional water vapor transport on the southern side of Huaihe River basin and zonal water vapor transport on its western side, and the influence of the two water vapor conveyance belts on summer precipitation in Huaihe River Basin both have experienced interdecadal increase.
Key words:Somalia cross-equatorial flow/
Huaihe River basin/
Summer precipitation/
Decadal
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