西北太平洋强TC频数与ENSO年际相关的年代际变化的机理研究

Many studies suggested that the tropical cyclone (TC) activities in western North Pacific (WNP) are related to ENSO. More TCs form in the southeast quadrant with more intense TCs in the El Nino developing year and more TCs form in the northwest quadrant with more weak TCs in the La Nina developing year. On the other hand, we found that the relationship between Nino3.4 index and the frequency of intense TCs has a decadal variation. During 1969-1988, the frequency of intense TCs has not correlated to ENSO significantly. Intense TCs are less active over the WNP while more active over the South china Sea (SCS) with the annual intense TCs being 4.85. However, the relationship between the frequency of intense TC and Nino3.4 index is very significant during 1949-1968 and 1989-2008, with more intense TCs over the WNP and less intense TCs over the SCS with annual number being 7.60 and 7.75, respectively. The monthly frequency of intense TCs has two extrema, that occurred in July and October during 1969-1988, while only one extremum that occurred in August during 1949-1968 and 1989-2008. This proposed project will be dedicated to the investigation of the mechanism responsible to the decadal variation of the relationship between ENSO and the frequency of intense TC and the mechanism of the decadal variation of WNP TCs genesis loaction, frequency, traks and seasonal cycle.

许多学者研究发现西北太平洋（西太）热带气旋（TC）的年际活动与ENSO有密切关系, El Nino发展年TC生成位置偏东偏南, 强度偏强；La Nina发展年，TC生成位置偏西偏北，强度偏弱。然而我们最近研究发现，1949-1968（第一阶段）和1989-2008年间（第三阶段）强TC频数与ENSO关系密切，而在1969-1988年间（第二阶段）两者相关并不显著。而且在第二阶段，强TC频数偏少，平均每年只有4.85个，其活动在西太偏少，南海偏多，而第一、三阶段强TC频数偏多，年平均分别为7.60和7.75个，在西太活动偏多，南海偏少。第二阶段强TC频数的季节演变与第一、三阶段单峰型也显著不同，呈双峰型。因此本项目拟研究ENSO与西太强 TC频数的年际相关的年代际变化的可能机理，以及与之相关的西太强TC频数，生成区域，路径，和季节演变的年代际变化规律及其机制。

本项目顺利完成了预期研究任务。1）揭示了PDO或者全球变暖对ENSO-西北太平洋TC生成频数关系的年代际变化机理，发现ENSO与7-11月强TC频数关系在1980s年代以来年代际增强，与1980s年代以来热带太平洋的SSTA西移有关，而ENSO与10-12月台风相关性与PDO的调制有关；2）深入分析了西北太平洋TC盛行路径的年代际转移及其机理：TC盛行路径在1980s年代末、1990s年代末，均发生了年代际际转移，移动路径以西北向移动为主，西移路径和东北转向路径偏弱，这种年代际变化主要受WNP北部的低层气旋异常、WNP南部的低层反气旋异常影响；3）深入细致评估了IPCC-AR4模式对影响西北太平洋TC的大气动力环境场的气候特征模拟性能；4）深入分析了热带季节内振荡和准双周振荡对西北太平洋TC生成的调制作用，认为低层涡度和中层相对湿度是影响西北太平TC生成的最重要的两个因子；5）探讨了东亚夏季PJ遥相关型的年际及年代际变化机理，认为PJ型态的年代际变化只与热带印度洋SST的年代际变化有关，而热带印度洋SST的年代际变化与IPO联系密切。这些深入细致的研究加深了对西北太平洋TC频数、路径、强度年际、年代际变化规律的理解。