摘 要 对比强厄尔尼诺次年2016年和1998年长江中下游梅雨季风环流异同点，并探讨其物理机制，结果表明：（1）2016年梅雨期和1998年两段梅雨期季风环流有诸多相似特征： 副高（西北太平洋副热带高压）偏强偏西, 南亚高压偏强偏东,孟加拉湾到南海西南季风偏弱；此外，华北东部到江淮均有冷槽维持; 副高持续稳定地将西南季风引导至长江中下游形成强西南暖湿气流，并与来自冷槽的北方南下干冷空气辐合，在高层辐散形势配合下形成强降雨。（2）3段梅雨期，青藏高原附近均为高压脊控制，受暖平流及高原热源、梅雨凝结潜热等因素影响，青藏高原到江南、华南一带大气中高层呈大范围强温度正距平；印度尼西亚群岛附近洋面为海温正距平，对流和热源偏强；此两因素是季风环流相似特征形成的重要原因。（3）2016年梅雨期，青藏高原暖脊最强，东部冷槽最浅，海温正距平范围最大最北，因而南亚高压和副高位置最北，梅雨雨带也最北；梅雨结束后，中高纬地区无持续冷空气南下，菲律宾以东洋面、南海及东海海域海温正距平增强，对流活跃，因此，副高显著偏北，不再出现第2段梅雨。（4）1998年7月中旬至8月初，青藏高原上空高压脊较浅，北部呈位势高度负距平，冷空气势力较强，温度偏低，东部冷槽深，西北太平洋海温正距平区域维持不变，故南亚高压和副高异常偏南，从而出现第2段梅雨。
Abstract The similarities and differences of monsoon circulation during Meiyu in the Middle and Lower Reaches of the Yangtze River between 2016 and 1998 following strong El Nino and the Physical Mechanisms are analyzed here. The results show that: (1) The monsoon circulation during Meiyu in 2016 and two Meiyu periods in 1998 has several similarities: WPSH ( Western Pacific Subtropical High ) is stronger and westward than usual, SAH(South Asia High) is stronger and Eastward, and Southwest Monsoon is weaker from the bay of Bengal to South China Sea. WPSH continuously guides Southwest Monsoon to the middle and lower reaches of the Yangtze River, forming a strong warm and humid southwest air flow, which converges with the dry and cold air from the cold trough, and forms heavy rainfall under the condition of high-level divergence.（2） During the three periods of Meiyu, there existed a warm ridge above Qinghai Tibet Plateau and nearby. The obviously positive temperature anomalies at middle-upper levels over most of Qinghai Tibet Plateau to Jiangnan and South China due to the warm advection ,heat sources over the Plateau and latent heat of condensation of Meiyu, Positive SSTA with strong convection and heat sources over Indonesian archipelago, both factors led to the similar characteristics of monsoon circulation. (3) In 2016, during the Meiyu period, the strongest warm ridge over Qinghai Tibet Plateau, the shallowest eastern cold trough, the greatest and the most northerly positive SSTA lead to the most northerly SAH and WPSH, and the most northerly Meiyu rain belt. After Meiyu, there was no continuous cold air flowing southward, and the positive SSTA over South China Sea, the eastern ocean of the Philippines and even the East China Sea increased rapidly with active convection, all these led to strong and northerly WPSH, so there is no longer a second Meiyu. (4) In 1998, from middle July to early August, the ridge over Qinghai Tibet Plateau was weak with negative geo-potential height anomalies,so the cold air over northern Qinghai Tibet Plateau was strong, the cold trough in the East was deep, and there was no significant change of positive SSTA in equatorial Northwest Pacific, so SAH and WPSH continued to be strong and abnormally southward, so that the second section of Meiyu appeared.