海洋性大陆区域加热异常与长江流域1998年夏季降水重大异常事件的联系

1998年夏季长江流域降水异常增多，发生了严重的洪涝灾害。本文利用1979-2011年的NCEP再分析月平均资料、Hadley中心的月平均海表温度资料和中国160站降水资料，分析了1998年夏季长江流域强降水的成因。结果表明：1998年夏季，印度尼西亚地区为非绝热加热正异常区，而其东北侧海域的非绝热加热为负异常或较小的正异常，由此形成了西南-东北向的异常加热梯度，使得印度尼西亚地区大气受到异常加热，低层辐合，高层辐散，而在热带西太平洋地区则为低层辐散，高层辐合，形成了西南-东北向垂直环流圈。热带西太平洋地区的低层异常辐散气流可作为异常涡度源，强迫出位于南海中国地区的反气旋性环流。同时，来自印度尼西亚北侧的扰动能量在南海地区辐合，有利于南海地区这一异常反气旋环流的维持。南海地区异常反气旋环流西北侧的西南气流，携带大量热带西太平洋及南海地区的水汽，输送到我国南方地区，并与控制中国东北地区的气旋性环流西南侧的西北气流交汇辐合于长江流域，有利于降水异常事件的产生。

Associations of the severe flood events over the Yangtze River basin in summer of 1998 with diabatic heating anomalies over maritime continent

By using the NCEP/NCAR reanalysis monthly data during 1979-2011, the monthly mean sea surface temperature data from Hadley center and precipitation data from 160 stations of China, the causes of severe rainfall over the Yangtze River basin in summer of 1998 were analyzed. Results demonstrate that a southwest-northeast abnormal heating gradient set up because of the positive anomaly of diabatic heating of Indonesia area and negative or slightly positive anomaly diabatic heating of its northeastern ocean areas, which makes the lower atmosphere convergent and the higher one divergent in Indonesia, and verse visa in tropical western Pacific, so a southwest-northeast vertical circulation circle was formed. Lower abnormal divergence of the tropical western Pacific air flow can be considered as abnormal vorticity source, which forced the anticyclonic circulation to occur in South China Sea. Moreover, the convergence of perturbation energy from the north side of Indonesia in South China Sea area is benefit for the maintaining of the abnormal anticyclonic circulation in South China Sea. The anomalous south wind flows in the western flank of the anti-cyclonic circulation brought abundant moisture to Yangtze River basin where the convergence of water vapor occurred, inducing strong rainfall there.