TYPHOON ACTIVITY IN NORTHWEST PACIFIC IN RELATION WITH EL NINO AND LA NINA EVENTS

Statistic and typical-year composition methods are used to study the northwest Pacific typhoon activities in relation with the EI Niño and La Niña events. The result indicates that the typhoon tends to be inactive in the EI Niño years and active in the La Niña years and it is also dependent on the onset and ending time and intensity of the events and areas of genesis of typhoons. With statistic features of the frequency of typhoon activity in the EI Niño and La Niña years and the time-lag correlation between the frequency and sea surface temperature(SST), useful information is provided for the prediction of typhoon occurrence. In addition, the singular values disassemble(SVD)method is applied to study the correlation between the geopotential field and SST field. The result shows that the air-sea coupling in the EI Niño years is unfavorable for the typhoon to develop. Which take place with a smaller number. Opposite situations are found with the La Niña years.     

THE CLIMATIC JUMP OF THE WESTERN PACIFIC WARM POOL AND ITS CLIMATIC EFFECTS

1INTRODUCTIONTropicalwesternPacificOceanisanareathathasthehighestoceantemperatureacrosstheglobe.Asmostofthewarmwaterconcentratesintheregion,itisknownasthe搘esternPacificwarmpool?Asshowninsomestudies[1-5],thegeneralcirculationandshort-termclimaticchangeswillbeseriouslyaffectedifthermodynamicconditionchangesinthewaters,whichthenhaveanimportantroletoplayintheonsetofanyENSOepisodes.Therehasnotbeenanyunifieddefinitionoftheindexforthewarmpool.FollowingthecriterionofWyrtki[4],however,theareae…     

印度季风与东亚夏季环流的遥相关关系

通过NCAR/NCEP再分析资料诊断发现印度夏季降水与东亚 5 0 0hPa位势高度有显著的相关性 ,形成了印度—东亚遥相关型 (IEA型 )。结合太平洋日本型 (PJ型 )的特征 ,指出PJ型主要决定夏季西北太平洋副热带高压的南北位置 ;IEA型在一定程度上影响副高脊西伸的东西经度或夏季中国大陆上空的平均位势高度距平。气候模式数值试验揭示出印度—东亚遥相关型对东亚很重要并且与印度洋海温异常有关 ,借此提出ENSO影响东亚夏季风的两条途径 :一条是直接路径 ,另一条为选择性路径。     

THE EFFECTS OF SEA SURFACE TEMPERATURE ANOMALIES OVER THE MID-LATITUDE WESTERN PACIFIC ON THE ASIAN SUMMER MONSOON

By Using the P-σ five-layer primitive equation model,three sets of numerical experiments are performedwith normal zonal mean SST(the control case),the positive SST anomalies in the Kuroshio current andeast-of-Japan Ocean(the midlatitude western Pacific),and positive SST anomalies over both the midlatitudeand the equatorial western Pacific.The experimental results show that the positive SST anomalies over themidlatitude western Pacific have great influence on the Asian summer monsoon:the Indian monsoon is weak-ened and the East Asian monsoon is intensified.This happens just reverse to the effects of positive SSTanomalies over the equatorial westero Pacific on the Asian summer monsoon.Further,the influence mechanismof the SST anomalies over the midlatitude westcrn Pacific on the Asian summer monsoon is discussed.     

西太平洋暖池混合层热力异常与我国东部夏季降水的关系

利用1981—2012年GODAS(Global Ocean Data Assimilation System)月平均次表层海温资料、混合层深度资料、NCEP/NCAR再分析资料及中国756个站的逐日降水资料,分析西太平洋暖池混合层热力异常与中国东部夏季降水的关系及可能的影响途径。结果表明,前期5月是西太平洋暖池(125~150 °E,0~18 °N)混合层热力异常影响我国东部夏季降水的关键期。在前期5月西太平洋暖池异常偏暖(冷)年,长江中下游流域的夏季降水偏少(多),黄河中下游流域夏季降水偏多(少)。1991—2012年,5月的西太平洋暖池热力异常呈现明显的变化趋势,由异常偏冷期向偏暖期转变。机制分析表明,由于前期5月西太平洋暖池热力异常,引起夏季菲律宾附近及其以东洋面和印度半岛中北部上空的对流活动、西太平洋副热带高压(简称副高)和南亚高压位置及强度的异常,进而影响水汽输送及上升运动,最终导致我国东部夏季降水的异常分布。      

热带西太平洋暖池和副热带高压之间的关系

文中研究了热带西太平洋暖池和西太平洋副热带高压的季节性变化和年际变化关系。结果表明,西太平洋暖池面积和副热带高压面积指数季节变化趋势基本一致,暖池中心的纬向移动与副热带高压西伸脊点相反,而经向移动和５００ｈＰａ副热带高压脊平均位置的南北季节性变化非常一致。西太平洋副热带高压的年际变化落后暖池大约３个月左右,用暖池２８℃或２９℃面积指数可以很好地预测出当年６,７,８三个月西太平洋副热带高压的面积指数。     

北太平洋海温异常与东亚夏季风相互作用的年代际变化

主要利用英国气象局提供的海温资料和ＮＣＡＲ／ＮＣＥＰ提供的４０年高度场及风场资料分析了东亚夏季风与北太平洋ＳＳＴＡ的关系，指出两者之间相互作用存在着年代际变化特征，７０年代中期以前，北太平海异常通过一大；圆波列作用于东亚夏季风，造成我国华北地区夏季降水偏多，７６年以后，北太平洋海温异常使大圆波列减弱，与东亚夏季风关系淡漠，不再影响华北降水。由此指出：影响东亚天气气候的海温关键区，并不总固定在某一海     

NON-LINEAR CRITICAL LAYER IN EL NINO AND LA NINA YEARS AND FORMATION, MAINTENTENANCE AND OSCILLATION OF THE SUBTROPICAL HIGH

Monthly mean zonal wind data from the European Center for Medium-range Weather Forecasting(ECMWF)for December 1982, April 1983, October 1984 and ApriI 1985 are used in numerical integration as thebasic flow in a non-linear critical-layer model. The subtropical high is extensive and limited in number if simulated with the basic now in December 1982 and April 1983. It consists of 2 to 3 cells that move westward at alloscillatory periods of 1～2 months. The subtropical high, simulated with the basic flow in October 1984 and April1 985. is weak and small in coverage, or distributed in strips that contain up to 4 cells. The high. merged or spillover a short time. is moving westward. The years 1982 ～1983 are a process of EI Niño while the years 1984-1985one of La Niña. lt is known from the chart of energy flux that it oscillates by a much larger amplitude and longerperiod in the EI Niño year than in the La Niña year. All the results above have indicated that the basic flow in the EI Niño year is enhancing the subtropical high lagging by about 4 months and that in the La Niña year is decay'ing it. It is consiStent with the well-known observational fact that the SSTA in the equatorial eastern Pacitlc ispositively correlated with the extent and intensity of the subtropical high in west Pacific lagging by 1～2 seasons.The result is also important for further study of the formation, maintenance and oscillation of the subtropicalhigh.     

INTERANNUAL VARIATION IN HEAT CONTENT OF THE WESTERN PACIFIC WARM POOL AND ITS EFFECT ON EASTERN ASIAN CLIMATE ANOMALIES

Using the 1980-2010 winter GODAS oceanic assimilations, study is conducted of the winter heat content (HC) established in the subsurface layer (5 to 366 m in depth) over the western Pacific warm pool (WP), followed by investigating the HC spatiotemporal characteristics, persistence and the impacts on the climate anomalies of neighboring regions. Results are as follows: 1) the pattern of integral consistency is uncovered by the leading EOF1 (PC1) mode of HC interannual variability, the year-to-year fluctuation of the time coefficients being well indicative of the interannual anomaly of the WP winter subsurface-layer thermal regime. The HC variation is bound up with ENSO, keeping pronounced autocorrelation during the following two seasons and more, with the persistence being more stable in comparison to SSTA in the equatorial middle eastern Pacific; 2) the winter HC anomalies produce lasting effect on the WP thermal state in the following spring and summer and corresponding changes in the warm water volume lead to the meridional transport and vertical exchange of warm water, which exerts greater impacts upon the sea surface temperature/heat flux over the warm pool per se and neighboring regions, especially in the Philippine Sea during the posterior spring and summer; 3) the increase in the winter HC corresponds to the spring OLR decrease and richer precipitation over the waters east to the Philippine Sea and the resultant convective heating anomalies are responsible for the rise of geopotential isobaric surfaces over tropical and subtropical western North Pacific, thereby producing effect on the western Pacific subtropical high (anomaly). Subsequently, the sea-surface heat flux exchange is intensified in the warm pool, a robust anomalous cyclone shows up at lower levels, air-sea interactions are enhanced and abnormal convective heating occurs, together making the winter HC anomalies even more closely associated with the variation in the summer subtropical high. As a result, the WP winter HC can be used as an effective predictor of the variation in spring/summer western Pacific subtropical high and the strength of summer monsoon over the northwestern Pacific.     

NUMERICAL EXPERIMENT OF IMPACT OF SEA SURFACE TEMPERATURE IN SOUTH CHINA SEA AND WARM POOL/WEST PACIFIC ON EAST ASIAN SUMMER MONSOON

By using the NCAR CCM1 model, we have designed six sensitive experiments, which areincreased and decreased SST (sea surface temperature) by 1℃ each in the SCS (South China Sea)and in the West Pacific warm pool, increased and decreased SST by 1℃ in the warm pool withincreased SST by 1℃ in the SCS. All experiments are integrated from April to July. Comparingwith the control experiment, we have analyzed the anomalies of the wind field at the upper andlower layers, the anomalies of the seasonal variability of the monsoon and precipitation for eachexperiment. In the result, we have found that the SST anomaly (SSTA) in the SCS greatly affectsthe seasonal variability of the SCS monsoon and precipitation in China, especially during the coldperiod of SST in the SCS. The impact of SSTA in the warm pool on SCS monsoon is also found.but is weak as compared to the effect of SST anomaly in the SCS. Besides, its impact on rainfall inChina is uncertain.     

THE EFFECT OF WARM POOL THERMAL STATES ON TROPICAL CYCLONES IN THE WESTERN NORTH PACIFIC

The influence of thermal states in the warm pool on tropical cyclones (TCs) in the western North Pacific (WNP) is investigated. There are fewer typhoons during warm years of the warm pool in which tropical storms tend to form in the northwest quadrant and move westward. Inversely, typhoons tend to recurve northeastward to the southeast of Japan and increase in number in the southeast quadrant during cold years. Based on composite analyses, circulation-induced dynamic factors rather than thermal factors are identified as being responsible for TCs activities. During the warm state, the monsoon trough retreats westwards, which leads to anomalous vorticity in low-level and divergence in high-level in the western part of west Pacific. Above-normal TCs activity is found in this area. Furthermore, wind anomalies at 500 hPa determine the main track types. On the contrary, when the warm pool is in cold state, the atmospheric circulation is responsible for the formation of more TCs in the southeast quadrant and recurving track.     

亚洲热带夏季风的首发地区和机理研究

文中分析了多年逐候平均 85 0hPa风场和黑体辐射温度等物理量的时空演变 ,结果表明 ,90°E以东的孟加拉湾、中南半岛和南海是亚洲热带夏季风首先爆发的地区 ,爆发时间在 2 7～ 2 8候 ,具有突发性和同时性。 90°E以西的印度半岛和阿拉伯海是热带夏季风爆发较晚的地区 ,季风首先在该区 10°N以南爆发 ,时间约在 30～ 31候 ,然后向北推进 ,6月末在全区建立 ,爆发过程具有渐进性。机制分析表明 ,由于 110～ 12 0°E的中高纬东亚大陆在春季和初夏地面感热通量、温度和气压的迅速变化 ,使热带低压带首先在该处冲破高压带 ,生成大陆低压 ,并引导西南气流在 90°E以东地区首先建立。在 90°E以西的印度半岛地区 ,地面感热通量在 4～ 5月间几乎没有明显变化 ,因而印度季风比南海季风晚爆发约 1个月。由此得出 ,90°E是东亚夏季风和南亚夏季风的分界线。此外 ,还着重探讨了南亚高压的季节变化与亚洲热带夏季风爆发的时间联系。发现南亚高压中心位置与亚洲热带夏季风爆发时间有较好的对应关系。南亚高压中心跳过 2 0°N时 ,南海夏季风爆发 ,跳过 2 5°N时 ,印度夏季风在其南部爆发。将用上述方法确定的爆发时间与用其他方法确定的爆发时间相比较 ,发现它们在南海地区有较好的一致性 ,在印度地区略有差异。     

1999年东亚夏季风异常活动的物理机制研究

文中从海-气相互作用的角度探讨了1999年东亚夏季风及与其相联系的雨带异常活动的物理机制。结果表明,由于1998年春季至1999年南海-热带西太平洋出现了近20 a最强的异常暧海温,该地强异常海-气相互作用的维持使得这种局地的热力强迫成为1999年东亚夏季风和降水异常的最主要外强迫机制,并使得1999年的季风活动和降水分布有别于一般的统计情形。从1998年秋到1999年,由于热带大气对南海-西太平洋暧海温所诱发的局地强加热的响应,热带西太平洋地区所出现的Gill模态的异常环流分布从冬季一直发展到夏季,并因此在海洋和大气之间形成了局地的强烈正反馈,不仅使得异常环流得以持续发展,而且也使得暖海温得以维持,成为影响1999年环流异常的最强前期信号。随着从冬到夏的季节演变,大气基本态对上述持续性异常环流的影响导致了冬、夏异常环流呈现出不同的纬向非对称,诱发了盛夏期间东亚到北美沿岸的遥相关波列。在东亚沿岸异常气旋性环流的影响下,大尺度异常东风在东亚沿岸的维持形成了极不利于季风西风在南海北部转向的条件,导致了季风在中国东部北进的异常偏弱和低纬西风转向位置的异常偏东。     

东亚冬季风与中国夏季气候变化

选取NCEP再分析高度场和风场资料、地面长波辐射(OLR)资料以及中国160个测站的降水资料，利用相关分析和合成分析方法，从资料分析入手来研究东亚冬季风异常变化及其对中国夏季降水的影响。研究表明：东亚冬季风有明显的年际和年代际变化特征，1950年代～1980年代中期为强冬季风时段，1980年代中期以后，季风明显减弱，为弱冬季风期。冬季风异常对中国大部分地区，特别对中国长江中下游地区的降水影响较大。分析进一步揭示了强弱东亚冬季风年后期海温分布和夏季流场明显不同的变化特征，并结合以前的许多研究对长江中下游地区降水异常形成的可能原因作了解释，指出正是由于这种不同的海温分布以及夏季环流的异常变化使得中国长江中下游地区在强(弱)冬季风年的夏季降水偏少(偏多)。     

INTERDECADAL VARIATIONS OF INTERACTION BETWEEN NORTH PACIFIC SSTA AND EAST ASIAN SUMMER MONSOON

Identification of key SST zones is essential in predicting the weather / climate systems in East Asia. With the SST data by the U.K. Meteorological Office and 40-year geopotential height and wind fields by NCAR / NCEP, the relationship between the East Asian summer monsoon and north Pacific SSTA is studied, which reveals their interactions are of interdecadal variation. Before mid-1970's, the north Pacific SSTA acts upon the summer monsoon in East Asia through a great circle wavetrain and results in more rainfall in the summer of the northern part of China. After 1976, the SSTA weakens the wavetrain and no longer influences the precipitation in North China due to loosened links with the East Asian summer monsoon. It can be drawn that the key SST zones having potential effects on the weather / climate systems in East Asia do not stay in one particular area of the ocean but rather shift elsewhere as governed by the interdecadal variations of the air-sea interactions. It is hoped that the study would help shed light on the prediction of drought / flood spans in China.     

亚洲夏季风建立格局和南海季风爆发特征及其成因初探

使用１９８０￣１９８６年欧洲中期预报中心（ＥＣＭＷＦ）格点资料和１９８０￣１９９２年日本地球静止气象卫星（ＧＭＳ）观测到的黑体辐射（ＴＢＢ）资料，分析了南海季风爆发和亚洲夏季风建立格局及其可能机制。发现亚洲夏季风建立征兆最早出现在中南半岛－南海地区，随后自该地区分别向西、向东扩展；中南半岛地区是东亚季风和印度季风的天然分界线，其两侧夏季风的建立特征和形成机制迥然不同。亚洲夏季风自东向西逐渐建立的格     

SEASONAL DEPENDENCE OF LOCAL AIR-SEA INTERACTION OVER THE TROPICAL WESTERN PACIFIC WARM POOL

Based on the air-sea interface heat fluxes and related meteorological variables datasets recently released by Objectively Analyzed Air-Sea Fluxes (OA Flux) Project of Woods Hole Oceanographic Institution, as well as the outgoing longwave radiation and surface wind datasets from National Oceanic and Atmospheric Administration, the seasonal dependence of local air-sea interaction over the tropical western Pacific warm pool (referred to the region (1o-6oN, 144o-154oE)) is revealed and the probable impacts of remote forcing on the air-sea interaction are examined. The results indicated the dominance of oceanic forcing with the significant impact of ENSO in March and that of atmospheric feedback without notable influence of remote forcing in June. While the interannual variability of sea surface temperature anomaly (SSTA) is larger than that of SSTA tendency when oceanic forcing is dominant, the opposite is true when atmospheric feedback is dominant. The magnitude of the oceanic forcing of the atmosphere tends to decrease in March with the occurrence of ENSO, though ENSO has little influence on the atmospheric feedback to the ocean in June. The local air-sea interaction is substantially the same before and after the removal of the effect of Indian Oceanic Dipole. The reduction of shortwave radiation fluxes into the western Pacific warm pool, due to the enhanced overlaying convection in March associated with ENSO, leads to the decline of SST tendency that will weaken the oceanic forcing of the atmosphere.     

A STUDY ON RELATION BETWEEN EAST ASIAN WINTER MONSOON AND CLIMATE CHANGE DURING RAINING SEASON IN CHINA

1 INTRODUCTION The Asian monsoon and its anomalies play an important role in the global general circulation and climatic change. As an essential component of the monsoon system, the East Asian winter monsoon is not only the most vigorous across the globe …     

东亚夏季风在中国东北区建立的标准、日期及其主要特征分析

文中利用中国东北区 80个测站 ,1980年以来近 2 0a逐日降水和同期NCEP/NCAR逐日再分析资料 ,提出了东亚夏季风在中国东北区建立和撤退的标准 ,即取 85 0hPa候平均资料 ,作沿 12 2 .5°E时间 纬度剖面图 ,将θse的336K和南风 4m/s等值线同时越过 4 0°N的候定义为东亚夏季风在中国东北区建立的日期 (候 ) ,持续及累积的总候数为影响时间 ;该年θse的 336K等值线永久撤离到 4 0°N以南的候为东亚夏季风从中国东北区撤退的日期 ;如果某年θse的 336K和南风 4m/s等值线没有同时北移越过 4 0°N的候出现 ,确定为东亚夏季风在中国东北区没有建立的年份。文中相应给出 1980～ 2 0 0 0年建立、持续及累积和撤退的时间年历表 ,经计算东亚夏季风在中国东北区建立的平均日期为第 4 1候 ( 7月第 5候 ) ,累积平均影响候数为 3.6候 ( 18d左右 ) ,开始撤退的平均日期为第 4 5候( 8月第 3候 ) ;东亚夏季风在中国东北区建立前后的候降雨量增加和撤退前后候降雨量递减十分显著 ,建立时水汽场由辐散转变为辐合。文中还定义了中国东北区强夏季风的年份 (建立的时间早 ,且累积候≥ 4候的年份 )为1981,1988,1990和 1994年 ,与国内学者定义的强夏季风年基本一致 ;在中国东北区没有建立东亚夏季风的年份为1980 ,1983,1987,1991,     

西太平洋暖池的跃变及其气候效应

用SST（COADS，NCEP）资料研究热带西太平洋暖池的年代际变化和跃变特征，讨论其气候效应。结果表明：西太平洋暖池有显著的10-20年周期的年人际变化和40-50年周期的气候跃变：一百多年来西太平洋暖池发生了4次大跃变，在1910年代中期和1950年代中期，西太平洋暖池由异常发展转为异常减弱，1930年代初和1980年代初，西太平洋暖池由异常减弱转为异常发展：西太平洋暖池在1980年代初的跃变，具明显的效应，跃变后热带中东太平洋海温显著升高，大范围海域升温超过0.5℃，夏季西太平洋副高加强西伸，脊线偏南，我国汛期降水呈南方偏多、北方偏少的分布趋势，与跃变前基本相反。研究结果还表明：在西太平洋暖池异常发展期，El Nino事件出现多且强于La Nina事件，而在西太平洋暖池异常减弱期，La Nina事件出现多且强于El Nino事件。