大气对热带热源低频响应的数值研究

本文设计—关于基本气流线性化的二层球面模式研究大气对不同类型赤道热源的低频响应,分析了全球大气40—50天低频振荡的结构和传播特点。结果表明:全球大气对热带热源响应特征是在热带地区表现为东西向非对称的热源东侧的Kelvin响应和西侧的Rossby响应,高低层反位相;在中高纬响应是具有低频振荡的二维Rossby波列,且具有相当正压结构。低频振荡的传播特征表明热带大气对移动性热源的响应更有利于振荡的向东传播,且该振荡可以沿波列路径向中高纬度传播,然后再折向低纬。二维Rossby波列是联系着热带和中高纬度地区低频振荡的基本动力学途径。该波列的形成取决于基本气流的分布,冬半球波列振幅较大。因此本文认为40—50天低频振荡是全球尺度的现象,它是一涉及到热带对流加热、赤道Kelvin波、亦道Rossby波、二维Rossby波列以及基本气流等动力学相互作用的过程。     

热带大气季节内振荡激发El Nino的机制

资料分析了表明,热带大气季节内振荡同Ｅｌ Ｎｉｎｏ发生有密切的关系。在Ｅｌ Ｎｉｎｏ事件发生之前,热带大气（尤其是赤道西太平洋地区）季节内振荡异常加强;伴随着Ｅｌ Ｎｉｎｏ的发生,热带大气季节内振荡动能明显增加。简单海－气耦合模式的分析表明,只有在年陵时间尺度大气外强迫作用下,海－气系统才可以产生类似ＥＮＳＯ模的耦合波。资料和理论模式分析和结果相结合,说明热带大气季节内振荡激发Ｅｌ Ｎｉｎｏ的机制     

2010年海洋和大气环流异常及对中国气候的影响

为了及时总结气候异常发生的成因,提高气候预测准确率,本文利用历史和实时观测资料以及物理机制诊断等方法,对我国2010年气候异常的成因进行了初步分析.结果表明,2010年是进入21世纪以来气候最为异常的一年.海洋异常特征主要有:2009年6月至2010年4月,赤道太平洋发生一次中等强度的厄尔尼诺事件,2010年7月又迅速进入拉尼娜状态;而热带印度洋海温距平的发展经历了全区一致型暖海温异常和负偶极型海温模态两个阶段;北大西洋海温距平表现为"三极子"型特征.受海温异常强迫和海气相互作用的影响,北半球大气环流的主要特征有:西太平洋副热带高压在10月之前受厄尔尼诺影响而异常偏强偏西,之后受拉尼娜影响而异常偏弱偏东,副高脊线位置也表现出明显的阶段性特征;夏季中高纬地区出现明显的阻塞形势;南海夏季风为1951年以来最弱的一年,东亚夏季风也异常偏弱.此外,2009/2010年冬季北极涛动出现近60年来最强负异常.在海温异常强迫和大气内部动力过程共同作用下的环流异常是造成2010年中国气候异常的主要原因.     

热带大气季节内振荡的异常与1997年El Ni~／no事件的发生

利用美国NCEP资料分析热带大气季节内振荡（ISO）NSO的关系，揭示了1997年El Ni~/no事件上的发生，与赤道中西太平洋地区大气ISO在1996年冬到1997年春期间的异常增强有重要关系。而且该地区ISO的异常增强并不主要由赤道印度洋地区移来，主要表现为ISO在印度尼西亚上空被激发增强和东传统。印度尼西亚地区ISO的被激发，则是由于东亚冬季风强异常在该地区引起的强对流活动的结果。     

热带印度洋上层洋流的动力统计诊断

作者对热带印度洋上层洋流作了空间的三维经验正交函数(EOF)分析,揭示其与印度洋偶极子和ENSO循环的关系.结果表明:热带印度洋上层流场偏差的前3个三维模态都具有赤道俘获波的性质,第一、二、三模态均具有2～4年的准周期,第一、三模态分别对应于第一、二类印度洋偶极子模态,第二模态则是ENSO在印度洋的延伸模态.由三维EOF各模态可直接计算各模态的垂直速度场.印度洋海温的年际变化主要取决于印度洋地区的海气耦合状态,然而ENSO循环也有很大影响,其影响也许是通过沃克环流的啮合作用来实现的.     

青藏高原动力和热力作用对热带大气环流影响的数值研究

应用在CCM3气候模式基础上发展的一个CCM3(R15L9)长期预报模式 ,进一步研究了青藏高原热力和动力作用对夏季热带地区大气环流的影响。结果表明 :在 6月初夏季节 ,青藏高原动力和热力作用在 30°N和 30°S一带有明显的增温效果 ,有利于北半球副热带西风减弱北移、热带高层东风增强北进、南半球西风带北压和赤道中低层西风形成和加强。加速了季节转换过程 ,有利于增强越赤道气流和南北半球的大气交换作用 ,还有利于在南海、菲律宾以东海面上热带气旋的形成和发展 ,以及140°E以东热带太平洋地区的东风波动的形成和发展     

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。     

A STUDY OF CLIMATOLOGICAL ASPECTS OF FLOW FIELD AND HEAT EXCHANGE ON TROPICAL PACIFIC SURFACE IN THE EL NINO AND LA NINA EVENTS

In this paper, based on the 2°× 2° grid data COADS from 1950—1987 the flow field and heatexchange anomalies on the tropical (11°S—11°N, 120°E—80°W) Pacific surface (TPS) are studiedin El Nino and La Nina events. During E1 Nino, the zonal pressure gradient and the trade windsdecrease on the TPS, the tropical convergence strengthens on the TPS, especially on the centralTPS, the sensible and latent heat exchanges increase, the net longwave radiation and incident solarradiation decrease and the net gain (loss) of heat reduces (increases) on the central and easternTPS. During La Nina the results turn out the contrary. Finally, two feedback mechanisms whichinclude the dynamic, thermal and hydrological processes during E1 Nino and La Nina are summa-rized and a conceptive model for El Nino-La Nina cycle is given.     

STUDY ON AIR-SEA HEAT EXCHANGE MECHANISM IN EL NINO AND LA NINA EVENTS

2°×2° mean monthly COADS grid data in 1974 and 1987 of E1 Nino and La Nina years are used to compute thesensible and latent heat fluxes,the net longwave radiation,the incident solar radiation and heat budget on the tropicalPacific surface(30°S—30°N).The difference of the heat budget between El Nino and La Nina mainly occurred on theequatorial ocean surface,especially the water area west of Ecuador and Peru.During El Nino,the sensible and latentheat exchange increased,the net longwave radiation and incident solar radiation decreased and the net gain(loss) of heatreduced(increased) on the ocean surface.During La Nina,the circumstances were opposite.Finally an ideal model ofair-sea heat exchange mechanism for the El Nino-La Nina cycle is summarized. Key words:El Nino,La Nina,air-sea heat exchange,COADS grid data     

El Nino年和La Nina年的非线性临界层与副高的形成、维持和振荡

采用欧洲中心１９８２年１２月、１９８３年４月、１９８４年１０月和１９８５年４月的月平均纬向风场实际观测资料,作为非线性临界层模式的基本气流进行数值积分,得到：用１９８２年１２月和１９８３年４月的基流模拟出的副高强、范围大、数目少,维持２￣３个单体,且向西移,东西振荡周期１－２个月。用１９８４年１０月和１９８５年４月的基流模拟出的副高弱、范围小,成带状分布,数目多达４个单体,副高合并、分裂得较快,亦     

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.     

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.     

厄尔尼诺年和反厄尔尼诺年热带大气环流及几个主要系统的特征

对近十年出现的3个厄尔尼诺年和2个反厄尔尼诺年中4—10月的夏季热带平均流场及几个主要系统作了定量综合分析和对比,得到:它们的沃克环流和哈得莱环流、对流层低层ITCZ和对流层高层TUTT的位置以及40—50°E、145°155°E处的低层越赤道气流强度均和常年不同,它们各自的年际和月际之间的平均环流和主要系统的特征也有差别。      

厄尔尼诺和反厄尔尼诺事件与西北太平洋台风活动

用统计相关和典型年合成方法分析了厄尔尼诺和反厄尔尼诺事件与西北太平洋台风活动的关系，指出厄尔尼诺年台风活动减少，反厄尔尼诺年台风活动增加，而且台风活动与厄尔尼诺、反厄尔尼诺事件起始和终止时间、强度、台风生成区域有关。利用厄尔尼诺和反厄尔尼诺年台风活动频数的统计特征，及台风频数与海温等要素的时滞相关关系，为台风频数的预测提供了有益的信息。还应用奇异值分解方法，分析了高度场和海温场的相关关系。结果表明，厄尔尼诺年海气耦合作用将造成不利于台风发展的环流条件，因此台风偏少，反厄尔尼诺年则出现相反的情况。     

THE ROLE OF TROPICAL CONVECTION IN VARIATION OF INTRASEASONAL TELECONNECTIONS OF TROPICAL AND EXTRATROPICAL CIRCULATIONS

Based on ECMWF objective analysis data, the relationships between tropical convective activi-ties and extratropical circulation, as well as the low frequency kinetic energy, have been investigat-ed by making use of diagnostic analysis methods on the intraseasonal time scale in winters of 1983/1984 and 1986/1987. From this study, it is found that the different intensities of the tropical con-vective activities may bring about both the different intraseasonal teleconnection wave trains be-tween the tropics and the extratropics and the different dispersions of the low frequency wave ener-gy. Moreover, the tropical convection can be an important junction factor for the teleconnection ef-fect of the tropical and extratropical circulations on the intraseasonal time scale.     

NUMERICAL SIMULATIONS OF THE PACIFIC MERIDIONAL MODE IMPACTS ON TROPICAL CYCLONES ACTIVITY OVER THE WESTERN NORTH PACIFIC

Based on analyses of the relationship between Pacific Meridional Mode (PMM) and number of tropical cyclones (TCs) activity over the western North Pacific, the impacts of the PMM on Tc activity over the western North Pacific are studied using numerical simulations with an Atmospheric General Circulation Model (CAM3) of National Center for Atmospheric Research (of USA). The result shows that the PMM has impacts on the large-scale generating environment of TCs, thus affecting their number and strength. The numerical simulations using the NCAR CAM3 indicate that with the inclusion of the forcing from sea surface temperature (SST) of the PMM, there appears a decreased magnitude of the vertical zonal wind shear, large proportion of relative humidity, anomalous westerly wind at low levels and anomalous easterly wind at high levels, in association with anomalous cyclonic circulation at low levels and anomalous anti-cyclonic circulation at high levels over the tropical western Pacific. Thus, the PMM provides favorable environment for the typhoon genesis. In the sensitivity experiment, TCs have larger strength, lower SST at the center, stronger tangential wind at 850 hPa and intensified warm cores at high levels. In this paper, the simulation results are similar to that in the data analyses, which reveals the important impact of the PMM on TC activity over the western North Pacific.