东亚温带气旋不仅对我国的天气气候有重要影响，而且在全球能量和水份循环过程中扮演重要角色。尽管已有很多学者对蒙古气旋、江淮气旋等东亚温带气旋进行了深入研究，但全面系统地分析东亚温带气旋的季节、年际和年代际变化特征的工作还非常少。本项目组前期研究发现我国冬季气旋频次和强度在1980年代中期发生突变，这与东亚在1980年代初期东亚冬季风减弱、副热带急流减弱、极锋急流加强以及中纬度对流层低层斜压不稳定性增强是一致的。本项目基于850hPa相对涡度法追踪气旋，将之前冬季的研究拓展到春、夏、秋季，并运用两套不同的再分析资料（NCEP&ERA），全面系统研究包含我国在内的东亚温带气旋各个季节的气候特征、年际年代际变化情况，探讨东亚气旋如何响应全球气候变化，并讨论其对极端天气气候的影响，这对于全面认识东亚温带气旋的活动特征及其对全球变化的响应具有重要的科学意义。

Extratropical cyclones over East Asia have significant impacts on the weather and climate over China, and they are the main carriers for momentum, energy and water vapor transferring in the global climate system. Many researches have been done on Mongolian cyclones and Jianghuai cyclones, but systematic analyses dealing with seasonal characteristics and decadal variations of East Asia extratropical cyclones are still rare in the literature. Our previous studies found the wintertime East Asia cyclone frequency and intensity had an abrupt change in the middle 1980s. Furthermore, the trend was also found to be consistent with the weakening of East Asia winter monsoon, the weakening of subtropical jet, the strengthening of polar-front jet, and the increasing trend of low-level baroclinic instability during the same period. This project will extend our winter research to spring, summer, and autumn, using two reanalysis data (NCEP&ERA), based on relative vorticity at 850 hPa (ξ850) to identify tracks of cyclones. The main objective of this study is to obtain an updated cyclone seasonal climatology over China/East Asia, and investigate the seasonal variations in cyclone frequency and intensity. Moreover, the mechanism for cyclone activity changes will be figured out, and how much of the extreme weather events can be explained by severe cyclones will be explored. These results will give us a better understanding of East Asia extratropical cyclones.