大气热源年代际异常与20世纪70年代末期东亚夏季风年代际减弱

利用1958-2001年ERA-40再分析资料计算大气热源,统计分析了亚洲季风区及其邻近海域大气热源年代际变异的典型模态;利用线性斜压干模式,模拟了夏季大气对大气热源年代际异常的响应,揭示了大气热源年代际异常与1970s末期东亚夏季风年代际减弱的关系。结果表明:近50 a来亚洲及其邻近海域夏季整层大气热源变异主要表现为年代际变化特征,其年代际位相转换发生在1970s中后期,这与东亚夏季风年代际减弱的时间一致;菲律宾附近海域和中国西南地区是与东亚夏季风年代际减弱有直接联系的两个热源异常关键区;东亚夏季风年代际减弱最直接地表现为这两个关键区热源异常的共同作用,而赤道中东太平洋、赤道印度洋大气热源增强则通过大气遥响应机制影响菲律宾附近海域低层大气环流异常对东亚夏季风变异起相反的贡献。

Interdecadal anomaly of atmospheric diabatic heating and interdecadal weakening of East Asian summer monsoon at the end of 1970s

Based on the ERA-40 reanalysis data from 1958 to 2001, the seasonal atmospheric diabatic heating was calculated, and the typical pattern of interdecadal variability of the atmospheric diabatic heating over East Asian summer monsoon (EASM) area and its adjecent sea areas was indentified. Furthermore, by using the global atmospheric baroclinic dry model, the steady atmospheric response to the interdecadal diabatic heating anomaly was simulated, and the relation between the interdecadal anomaly of atmospheric diabatic heating and the weakening of EASM at the end of 1970s was revealed. Results show that over the past 50 years, the vertically-integrated atmospheric diabatic heating variations over the Asia and its adjecent sea areas during summer are mainly characterized by interdecadal variations with an interdecadal transition occoured at the end of 1970s, whose occurring time is consistent with the phase change of the EASM weakening. The Philippine Sea and Southwest China are two key regions of significant diabatic heating anomalies that are directly related to the EASM weakening. The interdecadal weakening of EASM is directly associated with the joint effect of the above two key regions. The enhanced diabatic heating over equatorial eastern and central Pacific and equtorial Indian Ocean can cause opposite EASM anomaly by remotely affecting low-level atmospheric circulation over the Philippine Sea.