东亚高层纬向风季节内振荡与盛夏登陆中国大陆热带气旋频数年际变化的联系
投稿时间:2019-04-12  修订日期:2019-08-18  点此下载全文
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谢洁宏 南京信息工程大学气象灾害教育部重点实验室/大气科学学院 jiehongx@foxmail.com 
余锦华 南京信息工程大学气象灾害教育部重点实验室/大气科学学院  
钱晓蕾 南京信息工程大学气象灾害教育部重点实验室/大气科学学院  
叶梦茜 南京信息工程大学气象灾害教育部重点实验室/大气科学学院  
叶天 南京信息工程大学气象灾害教育部重点实验室/大气科学学院  
基金项目:国家重点研发计划重点专项(2018YFC1505800),国家自然科学基金(41575083)
中文摘要:使用1979-2017年欧洲中心提供的ERA-Interim再分析资料与中国气象局-上海台风研究所(CMA-STI)、美国联合台风警报中心(JTWC)整编的西北太平洋热带气旋(TC)资料,分析东亚高层(200 hPa)纬向风季节内振荡(ISO)与7-8月登陆中国大陆TC频数年际变化的联系。结果表明: 7-8月登陆TC频数存在年际变化,登陆频数与西风急流出口区南侧(北侧)纬向风为显著负(正)相关,基于显著相关区定义的东亚西风急流指数(EAWJI)可定量描述西风急流的经向移动;EAWJI与登陆TC频数为显著负相关,即EAWJI为负异常时,西风急流北移,登陆TC偏多,反之急流南移,登陆TC偏少;当急流北移,中国东部TC活动区域对流层呈现偏东风异常,产生了异常东风切变,有利于TC登陆过程的维持,使登陆中国大陆的TC频数增多。 东亚高层纬向风ISO与年际变化的标准差场、EOF典型模态的高度相似性说明两者由同一空间主导模式所控制,表明若ISO偏北偏南条件发生频率不对称,剩余偏差将改变季节平均。TC登陆多年,东亚西风急流指数ISO呈现出更高的偏北条件发生频率,引起急流出口区南侧ISO尺度扰动涡度通量的辐合,使急流位置发生北移,说明高层纬向风ISO可通过间接调制影响TC登陆的大尺度环流场进而与登陆TC频数的年际变化相联系。
中文关键词:登陆热带气旋  东亚高层纬向风  季节内振荡  年际变化
 
The relationship between Intraseasonal Oscillation of East Asian Upper-level Zonal Wind and the Interannual Variation in the Frequency of Tropical Cyclone Landfall over Mainland China in midsummer
Abstract:Using ERA-Interim reanalysis datasets and the tropical cyclones (TC) best-track data from China Meteorological Administration (CMA) and Joint Typhoon Warning Center (JTWC) during 1979-2017,this study analyzes the relationship between intraseasonal oscillation (ISO) of East Asian upper-level (200-hPa) zonal wind and the interannual variation in the frequency of tropical cyclone landfall over mainland China during boreal summer. The results show that the TC frequency of landfall in July-August presents a significant interannual variation.An East Asian Westerly Jet Index (EAWJI),which represents the meridional migration of the westerlies,is defined based on two regions where significant correlations exist between TC landfall frequency and 200-hPa zonal wind. EAWJI and TC landfall has a significant negative correlation.That means when negative (positive) anomaly appears,westerlies shows up in northern (southern) position and TC landfall frequency may increase (decrease).When the westerly jet moves to the north, the troposphere in the TC active region presents anomalous easterly winds, resulting in abnormal easterly shear, which is conducive to maintaining the TC landfall process and increasing the frequency of TC landfall in mainland China. The high similarity of standard deviation and EOF modes about East Asian upper-level zonal wind’s ISO variation and interannual variation indicates that they are governed by a common mode of spatial variability.It shows that asymmetric frequency of north (south) conditions would generate residual deviations and change the seasonal mean.In Landfall High-Frequency years,ISO-filtered EAWJI shows a higher frequency of north conditions,which cause the convergence of ISO-scale transient eddy flux in the south of the westerly jet exit and lead the westerly jet to drift north.Therefore,by modulating the large-scale circulation which affect the process of TC landfall,ISO of 200-hPa zonal wind can be connected with the interannual variation of TC landfall frequency indirectly.
keywords:Tropical cyclone Landfall  East Asian Upper-level Zonal Wind  Intraseasonal Oscillation  Interannual Variation
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