ENSO and Western North Pacific tropical cyclone activity simulated in a CGCM

A high-resolution (T213) coupled ocean–atmosphere general circulation model (CGCM) has been used to examine the relationship between El Niño/Southern Oscillation (ENSO) and tropical cyclone (TC) activity over the western North Pacific (WNP). The model simulates ENSO-like events similar to those observed, though the amplitude of the simulated Niño34 sea surface temperature (SST) anomaly is twice as large as observed. In El Niño (La Niña) years, the annual number of model TCs in the southeast quadrant of the WNP increases (decreases), while it decreases (increases) in the northwest quadrant. In spite of the significant difference in the mean genesis location of model TCs between El Niño and La Niña years, however, there is no significant simultaneous correlation between the annual number of model TCs over the entire WNP and model Niño34 SST anomalies. The annual number of model TCs, however, tends to decrease in the years following El Niño, relating to the development of anticyclonic circulation around the Philippine Sea in response to the SST anomalies in the central and eastern equatorial Pacific. Furthermore, it seems that the number of model TCs tends to increase in the years before El Niño. It is also shown that the number of TCs moving into the East Asia is fewer in October of El Niño years than La Niña years, related to the anomalous southward shift of mid-latitude westerlies, though no impact of ENSO on TC tracks is found in other months. It is found that model TCs have longer lifetimes due to the southeastward shift of mean TC genesis location in El Niño years than in La Niña years. As the result of longer fetch of TCs over warm SST, model TCs appear to be more intense in El Niño years. These relationships between ENSO and TC activity in the WNP are in good agreement with observational evidence, suggesting that a finer-resolution CGCM may become a powerful tool for understanding interannual variability of TC activity.     

基于改进的累积气旋能量指数评估西北太平洋TC活动与ENSO的关系

采用1977—2008年日本气象厅(JMA)TC最佳路径集资料和美国气候预测中心(CPC)的ENSO资料,设计了一个考虑热带气旋(TC)尺度信息的累积气旋能量指数(SACE),据此分析了西北太平洋TC活动与ENSO之间的关系。结果表明:相比于不考虑尺度效应的ACE,引入TC尺度信息的SACE增加了较大强度、较大尺度TC活动水平的权重,能够更加准确地刻画TC强度及其影响,其与Ni1o指数的相关性进一步增强。SACE能够更好地表征西北太平洋TC活动与ENSO年际变化的关系,其对ENSO位相的依赖性相对于ACE更为敏感,是一个能更好预测ENSO状态的因子。TC强度、生命史、频数以及尺度均对SACE有一定的贡献,但生命史的贡献最大,这一方面说明ENSO主要通过调制TC生命史来影响SACE,另一方面也说明相对于强度、频数和尺度而言,TC生命史更能影响SACE中的ENSO信号。     

GRAPES-TCM对登陆热带气旋降水的预报及其性能评估

基于GRAPES-TCM对2006年登陆热带气旋的降水预报结果,对该系统的24 h和6 h降水预报能力进行评估,并与基于卫星降水反演的外推预报(TRaP,Tropical Rainfall Potential)和相似台风降水预报技术(Analog Prediction Technique for Ty-phoon Precipitation,TAPT)进行对比.各方法对登陆热带气旋降水的综合预报能力通过分析预报和观测降水散点图、预报平均绝对误差(MAE)及均方根误差得到,降水分布型态的预报能力通过计算预报和观测降水的相关系数估计.此外,还分析了BS、POD、FAR、ETS评分等常用降水预报评估指标.结果显示,GRAPES-TCM的24 h降水预报绝对误差和均方根误差比TRaP和TAPT都大.但是,GRAPES-TCM的24 h降水预报与观测降水的相关系数远比TRaP和TAPT高.对其他指标的分析表明,GRAPES-TCM的漏报率远低于TRaP和TAPT,但3种方法的空报率在同一水平;对任一强度的降水,GRAPES-TCM的ETS评分总是最高,TRaP和TAPT对于大暴雨以上的强降水则几乎没有预报能力.对24小时内每6 h的降水预报,3种方法相对性能与24 h总降水相似.通过对各强度降水造成的降水量在总降水量中的百分比的对比分析,发现GRAPES-TCM预报强降水占总降水量的比重与观测十分接近.总体上说,GRAPES-TCM能较好地预报出登陆热带气旋降水的分布型态,对强降水的预报能力强于外推和相似预报方法,但是预报的降水量绝对误差偏大,尤其对暴雨级别以上降水,其BS值明显偏大.     

The influence of sea-surface temperatures on Eastern North Pacific tropical cyclone activity

The influence of sea-surface temperatures on six measures of tropical cyclone activity in the Eastern North Pacific is examined using historical sea-surface temperature and tropical cyclone data spanning from 1971 to 2002. Relationships are evaluated using methods of trend analysis, extreme year analysis, and bivariate correlation. Results suggest that in order to understand the climatological factors affecting topical cyclone activity in the Eastern North Pacific, the main development region must be divided into two sub-regions of development to the east and west of 112°W longitude. Increasing trends of sea-surface temperature are not accompanied by increasing trends in tropical cyclone activity. In the western development region, sea-surface temperatures are significantly correlated with all measures of tropical cyclone activity during extreme years. In this region, sea-surface temperatures are on average below the threshold for tropical cyclone development. In the Eastern development region, the only significant correlation with sea-surface temperatures is for the more intense measures of hurricane activity. In this region, sea-surface temperatures are on average above the threshold for cyclone formation. This leads to the hypothesis that the proximity to the cyclone formation temperature threshold in the WDR enhances the sensitivity of tropical cyclone activity to SSTs. This may have application to other tropical cyclone basins such as the North Atlantic.     

ENSO与中国东部地区8月降水年际关系的年代际变化特征及其机理探析

本文首先对ENSO与中国东部地区夏季逐月(6～8月)降水的年际关系进行了分析,结果表明NINO3区夏季海温与东部地区8月降水在整个年代尺度上改变显著,1974年以前的年际相关关系比1974年后显著,且1974年前后发生了年际相关型的改变.其次,1974年以前和1974年以后环流形势发生了明显变化.     

Structure of South Asia High in the stratosphere and influence of ENSO

The structure of the South Asia High(SAH)in the stratosphere and the influence of ENSO on the SAH are systematically investigated with the long-term ECMWF reanalysis data.The results show that the SAH only exists in low levels of the stratosphere.The maximum intensity of the High is located at around 150 hPa and there is no obvious anti-cyclonic structure above 50 hPa.The axis of the SAH center tends to be northwest slanting from lower levels to higher levels.Further analyses show that the geopotential height and temperature fields of the SAH have dramatic anomalies during El Ni?o years and La Ni?a years. Corresponding to the ENSO,the SAH is weaker(stronger)at the warm(cold)phase.     

ENSO与中国东部夏季降水异常关系的年代际变化

根据1960—2011年Had ISST资料集中的月平均海表温度资料和中国753站逐日降水资料,基于转经验正交函数分解等分析方法,发现中国夏季降水的变化具有明显的独立性特征,可以分为相对独立的11个雨区,并在此基础上讨论了11个雨区夏季降水与ENSO的相关关系及其年代际变化,发现不同雨区的夏季降水与ENSO相关关系的年代际变化特征不尽相同,据此可分为3种类型:第1类为稳定不相关型,代表区为东北地区、长江中下游地区、江南地区、闽赣地区、环琼州海峡地区;第2类为稳定相关型,代表区为河套地区、黄河中下游地区;第3类为相关关系变化型,代表区为辽吉地区、黄淮地区、淮河流域以及两广地区。而在第3类相关关系变化型中,4个雨区夏季降水与ENSO相关关系的年代际突变时间也存在差异,两广地区的突变年份在1975年左右,辽吉地区和黄淮地区的突变年份在1980年左右,淮河流域的突变年份在1985年左右。     

The Structure and Rainfall Features of Tropical Cyclone Rammasun （2002）

Tropical Rainfall Measuring Mission (TRMM) data [TRMM Microwave Imager/Precipitation Radar/Visible and Infrared Scanner (TMI/PR/VIRS)] and a numerical model are used to investigate the structure and rainfall features of Tropical Cyclone (TC) Rammasun (2002). Based on the analysisof TRMM data, which are diagnosed together with NCEP/AVN [Aviation (global model)] analysis data,some typical features of TC structure and rainfall are preliminary discovered. Since the limitations of TRMM data are considered for their time resolution and coverage, the world observed by TRMM at several moments cannot be taken as the representation of the whole period of the TC lifecycle, therefore the picture should be reproduced by a numerical model of high quality. To better understand the structure and rainfall features of TC Rammasun, a numerical simulation is carried out with mesoscale model MM5 in which the validations have been made with the data of TRMM and NCEP/AVN analysis.     

热带印度洋海温异常与ENSO关系的进一步研究

用1955年1月-2001年12月美国Scripps海洋研究所的海温再分析资料、美国NCEP再分析资料和美国气候预测中心(CPC)资料,讨论了热带太平洋ENSO与热带印度洋海温距平以及与印度洋偶极子(Dipole)的关系,研究结果发现:在垂直最大温度距平曲面(MTAL)上,热带印度洋海温距平分布存在着与热带太平洋ENSO密切相关的Dipole现象,其中最大的相关在太平洋ENSO 超前印度洋Dipole一个月.但是,热带印度洋Dipole的分布与Saij定义的位置略有不同,为东北西南向,它们分别在6°-10°S、65°-75°E(西印度洋)和2°-6°N、85°-95°E(东印度洋),它是赤道印度洋的一个主要海温距平系统.另外,在热带印度洋东北部与ENSO相关的海温距平是一个上下不一致的系统,该海温距平并没有伸展到海面,从海面到20-50 m的浅薄水层,则为与赤道西南印度洋相同符号的海温距平分布.因此在海面,海温距平不存在与ENSO有关的Dipole现象,赤道印度洋Dipole只存在于次表层以下,这是赤道印度洋Dipole与ENSO不同之处.这种赤道东北印度洋表层与赤道西南印度洋表层同符号的海温距平现象,有可能是海气热力过程如感热过程造成的.热带印度洋Dipole的周期要小于El Nio,一般为1-6 a.     

有关副热带太平洋对ENSO影响研究的综述

ENSO（El Niño-Southern Oscillation）的发生发展既受到来自热带西太平洋纬向海气过程的影响,也受到来自副热带太平洋经向海气过程的影响。本文概述了副热带太平洋海气异常影响ENSO研究方面的科学背景及研究进展,综述了前人提出的副热带太平洋大气海洋异常通过经向风应力以及北太平洋/南太平洋经向模态,影响ENSO发展演变的途径及相关物理机制,总结了近些年观测资料分析及数值模拟研究工作所提出的新观点,并讨论了相关研究中的学术分歧及有待进一步研究的问题。     

不同ENSO位相热带中东太平洋与低纬度大气的信息传输不对称性研究

基于传递熵和再分析数据,讨论了不同ENSO位相下热带中东太平洋与其上空大气的信息传输,研究结果表明:厄尔尼诺、拉尼娜及中性状态下均是以海洋输出信息、大气输入信息为主导的特征,且海洋和大气输入和输出信息的空间分布型较类似。相对中性状态而言,厄尔尼诺和拉尼娜状态下,海洋和大气输入和输出的信息均较强;拉尼娜状态相比厄尔尼诺状态,海洋与大气输入和输出的信息要稍强。通过重排滑动随机抽样方法分析了热带中东太平洋与其上空大气信息传输强度与海温异常的关系,重点分析了热带中东太平洋与其上空大气信息传输的不对称性。揭示了海洋对大气的信息传输随海温距平的变化可以分为类拉尼娜、类中性状态及类厄尔尼诺3个阶段:类拉尼娜阶段,随着低海温的减弱信息传输逐渐减弱;类中性状态,低海温向高海温的过渡过程,信息传输并不存在显著的变化趋势;类厄尔尼诺,随着高海温的增强信息传输逐渐增强。热带中东太平洋与其上空大气信息传输的不对称性更表现为类拉尼娜和类厄尔尼诺阶段信息传输与海温异常之间建立线性关系的阈值和线性趋势程度的不对称。此外,大气对海洋的信息传输随海温的变化与海洋对大气的信息传输随海温的变化类似,即海洋对大气信息传输较强时,大气对海洋的信息传输同样较强,反之亦然,并且大气对海洋的信息传输随海温的变化同样存在不对称性。     

Seasonal modulations of different impacts of two types of ENSO events on tropical cyclone activity in the western North Pacific

The paper examines different impacts of eastern Pacific warm/cold (EPW/EPC) and central Pacific warm/cold (CPW/CPC) events on tropical cyclones (TCs) in the western North Pacific (WNP) by considering the early season of April–June (AMJ), the peak season of July–September (JAS) and the late season of October–December (OND). During AMJ, EPW (EPC) is associated with a significant increase of the TC genesis number in the southeastern (southwestern) sub-region of the WNP, but no class of El Niño-Southern Oscillation (ENSO) events shows a significant change in the TC lifetime and intensity. During JAS, EPW corresponds to an increase (decrease) of the TC genesis number in the southeastern (northwestern) sub-region, but CPW shows no significant change. EPC increases the TC genesis in the northwestern and northeastern sub-regions and decreases the genesis in the southwestern sub-region, whereas CPC suppresses the genesis in the southeastern sub-region. Both the lifetime and intensity of TCs are increased in EPW, but only a shortened lifetime is seen for CPC. During OND, EPW reduces the TC genesis in the southwestern and northwestern sub-regions, whereas CPW enhances the genesis in the southeastern sub-region. Over the South China Sea, CPW and CPC show a significant decrease and increase of the TC genesis, respectively. The TC lifetime is significantly longer in both EPW and CPW and shorter in EPC, and TCs tend to be more (less) intense in EPW (CPC). All of these variations are consistent with the development of ENSO-related SST anomalies during different seasons and are supported by distributions of the genesis potential index—a combination of large-scale oceanic and atmospheric factors that affect TC activity. TCs in the WNP mainly take the straight westward, northwestward and recurving tracks. During AMJ of EPW years, the TC steering flow patterns favor the recurving track and suppress the straight westward and northwestward tracks. During JAS, EPW is associated with the steering flows that are unfavorable for TCs to move northwestward or westward, whereas CPW favors the northwestward track and suppresses the straight westward track. The steering flow patterns during OND are similar to those during JAS, except that EPC may increase the possibility of the northwestward track.     

影响广东的热带气旋与ENSO的关系

为探讨ENSO对影响广东的热带气旋的影响,利用统计方法对1950-2003年期间进入广东防区的热带气旋的累计气旋能量ACE变量和其他变量与ENSO的关系进行了分析,发现在年的尺度上进入广东防区的热带气旋对ENSO的响应很弱,且表现出明显的季节差异,在6-8月表现出与Nin03．4指数的正相关,而在10月份表现出明显的负相关。热带气旋的强度、数量、时间等在10月份都与Nino3．4指数表现出较明显的负相关,即在拉尼娜出现当年的10月份热带气旋趋向于数量增多,强风暴的生命史增长,影响时间较长,强风暴强度也趋向更强,破坏力增大;而在厄尔尼诺年,热带气旋趋向于数量减少,强风暴的生命史缩短,影响时间较短,强风暴会趋向减弱,破坏力会减低。分析可知,ACE指数很好地反映热带气旋对ENSO响应的特性。     

热带大气对非绝热加热的响应及其与ENSO循环关系

通过求解赤道β平面上的线性运动方程,研究了热带大气对主要由海洋热状况异常导致的大气非绝热加热的响应,并探讨了该过程与ENSO循环的关系。结果表明,非绝热加热的直接作用及其产生的Kelvin波、Rossby短波是大气零阶的扰动位势和纬向风速变化的原因。在El Nino期间,大洋西部首先发展出正的大气位势异常。但随着海洋热状况的正异常的持续,随之在大洋西部即开始孕育和发展,导致热带太平洋海气耦合系统回归正常状态,甚至是转向La Nina的大气异常状态或系统,其标识是非绝热的异常加热所激发的大气Kelvin波的产生和东传,并伴随正位势异常的大值向东移动和大洋西部正的位势异常减弱,信风由此而增强。在La Nina的盛期,海洋热状况存在负异常(即弱于平均状态),则将有相反的过程。     

基本气流在ENSO对北半球冬季大气环流影响中的作用

本文从观测事实、理论与数值试验来研究基本气流在ENSO事件对北半球冬季大气环流影响中的作用。通过观测资料的分析,发现1972/1973年冬ENSO现象发生时的基本气流与一般ENSO现象发生年份的基本气流不同,这使得该年冬季ENSO现象所引起的北半球大气环流异常与一般ENSO现象所引起的环流异常型不同。一般ENSO现象所引起的北半球大气环流异常型是PNA型,而1972/1973年冬北半球环流异常型是非PNA型,我国东北地区出现暖冬,冷空气活动弱。     

ENSO对印度洋偶极子与中国秋季降水关系的影响

利用1950--1999年Hadley中心全球海温资料、NCEP／NCAR再分析资料和中国气象局整编的160站降水资料，通过讨论印度洋偶极子（IOD）独立发生时及IOD与ENSO联合发生时中国秋季降水的差异，研究了ENSO对IOD与中国秋季降水关系的影响。结果表明：仅有IOD发生时，其正位相年使得中国西南地区和黄河流域的秋季降水出现正异常，而当IOD与ENSO伴随出现时，IOD正位相年和E1Nino使得中国西南地区秋季降水正异常区域维持并向东扩展，还使得黄河流域秋季降水转为负异常。此外分析了ENSO改变IOD与中国秋季降水关系的环流成因。     

Simulated impacts of two types of ENSO events on tropical cyclone activity in the western North Pacific: large-scale atmospheric response

The present paper uses an atmospheric general circulation model to explore large-scale atmospheric response to various El Niño-Southern Oscillation events associated with tropical cyclone (TC) activity in the western North Pacific. The simulated response is basically consistent with and confirms the observed results. For eastern Pacific warm (EPW) event, anomalously wet ascent occurs over the tropical central/eastern Pacific and dry descent is over the western Pacific. This Walker circulation is associated with anomalous low-level convergence, reduced vertical wind shear (VWS), and enhanced genesis potential index (GPI) in the southeast sub-region. These are consistent with the observed increase of the TC formation in the southeast sub-region but decrease in the northwest sub-region during July–September (JAS) and the increase in the southwest and northwest sub-regions during October–December (OND). In addition, the strong westerly anomalies of the TC steering flow prevail in the East Asian coast, suppressing the TC northwestward or westward tracks. For eastern Pacific cold (EPC) event, all of the simulated variables show almost a mirror image of EPW. For central Pacific warm event, the anomalous Walker circulation shifts westward because of the westward shift of the maximum SST anomaly forcing. The anomalous subsidence associated with the western branch of the Walker circulation during OND shifts northward to the South China Seas, resulting in a decrease of the TC genesis there. The TC steering flow patterns during JAS are favorable for TCs to make landfall over Japan and Korea. Compared with EPC, the descending motion in the central/eastern Pacific is much stronger for central Pacific cold (CPC) event, accompanied by more enhanced VWS and reduced GPI in the southeast sub-region. Therefore, CPC provides a more adverse environment to the TC formation there during JAS and OND, consistent with the observed decrease of TC formation there. Moreover, the easterly anomalies of the TC steering flow dominate the tropics during JAS, enhancing TC activity in the east coast of China. Additionally, the convection over the western Pacific moves to the South China Sea during OND, favoring the TC genesis there.     

ENSO冷暖事件与郑州地区汛期气候异常关系

利用1951～2000年郑州站汛期气温和降水资料,分析了ENSO冷暖事件与郑州地区汛期气候异常的关系.结果发现ENSO冷暖事件对郑州地区汛期降水和气温均有较大影响,对降水异常的影响更显著.暖事件出现当年,郑州地区汛期易出现降水异常偏少,次年则易出现降水异常偏多;冷事件出现当年,郑州地区汛期降水易出现异常偏多,次年降水出现异常的几率较小.