A STUDY OFTHE INTERACTION BETWEEN THEASIAN SUMMER MONSOONAND EL NINO-SOUTHERN OSCILLATION

利用海洋环流模式（OGCM）和NCEP/NCAR再分析，得到了厄尔尼诺-南方涛动（ENSO）对南亚夏季风年际变化的两个主要影响，即ES和EA影响。在20世纪60年代至70年代中期，ES的影响主要是由印度洋和太平洋的类似于tbo的ENSO主导的。在热带印度洋上空可以看到与ENSO增长有关的异常Walker环流的东移。与此相关的是夏末印度洋东西部海温纬向不对称异常的突出。从夏季到秋季，印度洋上空的赤道低空双异常环流被诱发，其北部对流层与印度上空的异常季风降雨动态相关，尤其是在夏末。如果类tbo ENSO模式具有精确的两年周期，则夏季风季总是与ENSO的生长期相对应，这意味着季风总是受到ES影响。相比之下，EA的影响需要持续的ENSO，而这种ENSO不会在北方春季结束，因为从前一个冬季到春末，菲律宾附近持续的异常对流加热触发了印度洋的西风反馈机制。由于长时间冷暖事件的频繁发生，20世纪70年代后期以后，EA对ENSO衰减期的影响变得显著。20世纪70年代末之前，类tbo ENSO生长期的ES影响导致了强烈的ENSO-季风耦合，而20世纪70年代末之后ENSO长期化的发生则导致了ENSO衰减期EA对季风的影响，且在季风季前期显著。与ES的影响相比，EA的影响是间接的，直到夏末才会持续。此外，20世纪70年代末以后的季风倾向于同时经历ENSO的ES和EA影响，尽管ES影响变得不那么明显。我们得出结论，这些特征导致了enso -季风关系在20世纪70年代末之后的减弱。少

Using an ocean general circulation model (OGCM) and NCEP/NCAR reanalysis, we obtained two major impacts (i.e., ES and EA impacts) of El Nino-Southern Oscillation (ENSO) on the South Asian summer monsoon interannual variability. The ES impact, which is dominated by TBO-like ENSO in the Indian Ocean and the Pacific Ocean, tends to prevail during the period from the 1960s to mid-1970s. Eastward migration of anomalous Walker circulation relevant to the growth of ENSO can be seen over the tropical Indian Ocean. Associated with this is the prominence of zonally asymmetric SST anomalies between the western and eastern parts of the Indian Ocean in late summer. Low-level twins anomalous circulation across the equator is induced over the Indian Ocean from summer to fall and its northern counterpart is dynamically linked with anomalous monsoon rainfall over India especially in late summer. If the TBO-like ENSO regime has a precise biennial periodicity, the summer monsoon season always corresponds … More to the growth phase of ENSO, which means that the monsoon is always affected by the ES impact.By contrast, the EA impact requires the prolonged ENSO that does not terminate in boreal spring because persistent anomalous convective heating in the vicinity of the Philippines from the preceding winter to late spring triggers a WES feedback regime in the Indian Ocean. Due to the frequent occurrence of the prolonged warm and cold events, the EA impact at the decay phase of ENSO becomes significant after the late 1970s. The ES impact at the growth phase of TBO-like ENSO brings about the strong ENSO-monsoon coupling prior to the late 1970s, while the occurrence of the prolonged ENSO after the late 1970s induces the EA impact on the monsoon at the decay phase of ENSO that is significant at the early stage of the monsoon season. Compared to the ES impact, the EA impact is indirect and not persistent until late summer. Furthermore, the monsoon after the late 1970s tends to experience both the ES and EA impacts of ENSO although the ES impact becomes less clear. We conclude that these features lead to the decline of the ENSO-monsoon relationship after the late 1970s. Less