中国北方秋雨与热带中太平洋海表冷却的关系

Relationship between Cooling of Tropical Pacific Sea Surface Temperature and Autumn Precipitation in China

本文利用1951～2011年中国160站降水、NCEP/NCAR再分析资料和NOAA延长重建海表温度(NOAA extended reconstructed SST)资料,研究了中国9月北方秋雨的年际变化特征及其成因,并用ECHAM5大气环流模式开展了数值试验,最后对2011年9月历史罕见秋雨进行了分析。研究发现,中国北方秋雨有明显的年际和年代际变化,19世纪60年代到1980年代中期,北方秋雨偏多,1950年代、1980年代后期和1990年代秋雨偏少。北方秋雨与西太平洋副热带高压的西伸有密切联系,北方秋雨偏多时,副热带高压偏西偏强,有利于偏南风向北输送水汽并在中国北方辐合。西太平洋副热带高压的加强西伸与热带中太平洋的海表冷却密切有关,偏低的热带中太平洋海表温度(CTSSTI)使其上的对流活动受到抑制,热带西太平洋对流异常旺盛,在西北太平洋出现异常反气旋,加强东亚—西北太平洋的EAP波列,引起西太平洋副热带高压明显西伸,导致秋雨偏多。反之,热带中太平洋海表偏暖,副热带高压偏弱偏南,秋雨偏少。2011年9月北方秋雨的环流异常及成因与统计分析和数值模拟结果基本一致。

Autumn precipitation in North China （APNC） is studied for 1951-2011 by using 160-station observed monthly precipitation in China, National Centers for Environmental Prediction/National Center for Atmospheric Research （NCEP/NCAR） Reanalysis data, National Oceanic and Atmospheric Administration （NOAA） extended reconstructed sea surface temperature （SST）, and the ECHAM5 general circulation model. In addition, the APNC and anomalous circulations recorded in September 2011 are compared with the statistical and numerical results. It is determined that the APNC shows dramatic interannual and interdecadal variability. The APNC was in a positive phase during the 1960s to early 1980s and in a negative phase in the 1950s, mid-late 1980s, and 1990s. Moreover, the strengthened APNC is closely related to westward stretching of the western Pacific subtropical high （WPSH）. The cooling SST in the central tropical Pacific depresses the atmospheric convection over the region and exerts Rossby waves to enhance the convection over the western tropical Pacific. The local Hadley circulation is connected to convection over same region. The strengthened local Hadley circulation leads to anomalous anticyclones in the northwestern Pacific and is favorable for the westwardmovement of the WPSH via East Asia-Pacific （EAP） teleconnection, which increases the APNC. In 2011, negative SST anomalies in the central tropical Pacific and anomalous circulation contributed to extreme above-normal precipitation, which is consistent with the statistical and model experiment results.