风应力的旋转和辐散分量有ENSO循环中作用的数值试验研究

将1960－1991年的月平均FSU风应力资料分解为旋转部分和辐散辐合部分,分别用以强迫模式海洋,所用的模式为一个2层热带太平洋区域海洋模式。结果表明,就季节变化而言,不论是用志分量还是散合分量强迫海洋,都不能产生合理的冷舌,哪怕将旋转或散合分量放大一倍或缩小二分之一,也不能使冷舌的强度和分布得到合理的改善,若采用气候平均的含有季节变化的风应力（未对旋转和辐射分量进行分离）,则可产一与帝际相符的海表温度分布。在此基础上,分别叠加旋转和辐散分量的年际异常部分,通过海洋的强迫,可产生海表温度异常。在年限异常旋转分际异常风应力的强迫下,则产生较弱的SSTA,且振荡频率较高,ENSO周期不很明显。这些结果说明,风应力的涡旋和辐散辐合分量在海温季节变化和年际变化的形成海洋方可产生,而仅有异常风应力的旋转强迫就可产生合理的FL Nino/La Nina现象,同时,风应力的辐散辐合分量在海洋平均状态的形成过程中是重要的,但在EN－SO过程中就对海洋的作用而言则不如旋转分量重要。     

热带西太平洋风应力异常在ENSO循环中作用的数值试验

利用一个中等复杂程度的海气耦合模式来研究热带西太平洋地区风应力异常对ENSO循环的影响,并以1997/1998年的El Nino事件为例,分析了模式结果中热带西太平洋地区风应力异常对El Nino事件形成影响的动力学及热力学作用.结果表明,热带西太平洋地区的风应力异常对ENSO循环有很重要的作用.在耦合模式中,当热带西太平洋地区的风应力异常由观测给定时,耦合模式基本上可以模拟出自1971年以来的EI Nino事件,观测与模拟的Nino 3区海面温度异常(SSTA)的相关系数可达0.63.赤道西太平洋地区的风应力异常可加强该地区大气的辐合,从而加强了大气的加热场,进而加强了海气相互作用的不稳定.赤道西太平洋地区西风异常激发出来的Kelvin波及水平平流对EI Nino事件初始阶段的发展起重要作用;海气相互作用及东边界的反射对EI Nino事件的发展及维持起重要作用.     

季节背景对ENSO循环过程中SSTA增/减幅作用的数值试验研究

利用热带太平洋地区 2层区域海洋模式和再分析资料探讨了大气 /海洋的季节背景对ENSO时间尺度上海温异常的增幅或减幅作用。结果表明 :不论什么季节背景下 ,就海洋变化而言 ,El Nino/La Nina事件均可存在 ,说明 El Nino/La Nina事件的存在和维持并没有季节性选择 ;模式海洋的西太平洋赤道地区次表层海水温度异常变化位相明显超前于东太平洋SSTA且在空间上自西向东传播 ,同时有位相超前的量还包括模式第 1层厚度异常及热容量异常 ,这些对 ENSO的预测和机制研究具有重要意义。 SSTA的振幅在不同的季节背景下可受到不同的调节。以春季为背景 ,同样的异常风应力作用于海洋 ,可使 NINO3区 SSTA较正常季节背景下该区的 SSTA振幅明显增大 ;而在冬季背景下可使 SSTA受到一定程度的减幅 ,这说明 El Nino/L a Nina现象的发生和消亡有季节选择倾向。与春季背景下 NINO 3区SSTA的增幅倾向相反 ,模式第 1层厚度异常的振幅则受到削弱。而西太平洋赤道地区 ,模式海洋混合层的厚度异常则有所增强。这种与 SSTA增 /减幅反相关的现象需要进一步研究     

有限区域旋转风与辐散风分解方案的选择

介绍一种具有“收敛”特性的有限区域旋转风与辐散风分解方案，并与目前常用后一些差分方案进行了比较，实际个例的计算和对比表明，该方案不仅考虑了区域内部强迫函数的作用，而且在迭代过程中加入边值的影响，因此具有极好的重建风场的能力，分解后的旋转风和辐散风在有关的诊断分析中使结果更为合理。     

ENSO对黑潮海区风应力异常影响的初步探讨

利用近50a黑潮海区风应力场与Nino3区海温指数序列进行相关分析后发现,ENSO对黑潮海区经向风应力影响的“关键时段”为秋、冬季至次年初夏时期,对纬向风应力影响的“关键时段”为冬季至次年春季。黑潮海区风应力距平场与赤道中东太平洋SSTA场的扩展SVD分析及相应的合成分析揭示了ENSO期间黑潮海区风应力异常结构的演变：秋季,中国的东海、琉球群岛附近海域首先出现南风应力异常;冬季,吕宋岛以北、台湾以东的海域出现西南风应力异常,其影响范围和强度在次年2月前后达到最强,其后迅速减弱,至5月,风应力异常基本消失。赤道中东太平洋SSTA对黑潮海区经向风应力异常的影响范围较大,强度更显著。     

与ENSO相联系的热带太平洋典型风应力异常场结构

利用多年逐月海温距平和风应力距平观测资料,运用线性回归和EOF分析方法,分析了与ENSO相联系的热带太平洋典型风应力异常场结构。结果显示,与ENSO线性相关的风应力异常场在时间尺度上表现为低频变化,在水平结构上主要表现为四个典型分布。其中,分布型1主要表现为日界线以东赤道地区东风异常和赤道风应力场辐散;分布型2主要表现为日界线以东赤道地区西风异常和经向异常风应力向赤道气流;分布型3主要表现为日界线以东赤道偏南地区西风异常和风应力场辐合,日界线以西为东风异常;分布型4主要表现为160°W以东的弱东风异常和160°W以西的西风异常。与ENSO线性无关的风应力场主要表现为高频过程,在水平空间结构上其典型场主要位于赤道外地区。还用与ENSO有关的那部分回归风应力异常场强迫海洋距平模式,成功地再现了ENSO的主要信号。这表现观测揭示的典型风应力异常型对于El Nino的产生是根本性的。      

风应力对SST气候场和年际变率作用的诊断及数值研究

相关方法分析Nino3区SSTA和风应力的关系，发现前期风应力距平场与Nino3区SSTA有很好的相关关系，这种相关性超前8个月时就有所显现。影响Nino3区SSTA的主要风应力区域的位置随风应力超前的时间缩短均向中太平洋扩展。数值试验方法研究不同区域的风应力对热带太平洋SST作用的结果表明，强相关区域的风应力对形成和维持热带太平洋SST的气候场的作用不明显，而对SST的年际变率有重要贡献；相反，强相关区域以外的风应力对形成和维持热带太平洋SST的气候场起重要作用，但是对SST的年际变率所起的作用很不理想。     

无旋转风分量在台风"桑美"急剧增强和急剧减弱过程中的分析和应用

利用日本气象厅区域谱模式(RSM)的20 km分辨率再分析资料,对2006年第8号台风"桑美"在近海急剧增强和登陆后急剧减弱时的高低层辐散、辐合特征进行了对比分析.结果表明,利用调和-余弦计算方法得到的无旋转风分量较散度场能更明显地反映台风"桑美"在近海急剧增强和登陆后急剧减弱时的风场变化特征.在台风急剧增强过程中,台...     

模拟的超级单体雷暴旋转和辐散分量的动能收支

一、引言实际发展中的强风暴,尤其是产生陆龙卷的强风暴的一般特点是,准定常旋转环流相对平均气流是倾斜的.Lilly(1982,1983)提出,旋转的发展首先是扩大风暴范围,进而使风暴结构稳定.在他1986年的文章里,他用线性分析方法指出了三维浮力对流元对平均气流垂直切变有反应,即增加绕垂直轴的旋转,从平均气流中获得旋转动能.通过进     

海洋对ENSO和其他时间尺度上风应力振荡的响应

利用带通滤波方法，将FSU风应力资料分离成ENSO时间尺度上的分量及其剩余部分，将这两部分分别作用于模式海洋（2层热带太平洋区域模式），研究海洋对不同时间尺度大气变化的响应。结果表明：尺管ENSO时间尺度上的风应力分量只占风应力扰动总方差的30％左右，它却能激发出全部异常风应力强迫海洋时所产生的El Nino/La Nina现象和十分相近的SSTA变化周期与振幅。而其余占总异常风应力方差60％以上的部分强迫海洋仅能产生振幅较小的海表温度异常，在非ENSO和ENSO时间尺度上的风应力强迫下，海洋中可产生相近振幅的Kelvin波，但SSTA振幅却存在显著差别，表明海洋对大气扰动信号的频率非常敏感，这里从理论上对该现象作了解释和说明。     

NUMERICAL STUDY ON THE ROLE OF VORTICAL AND DIVERGENT COMPONENTS OF WIND STRESS IN ENSO CYCLE

The 1960-1991 monthly mean FSU (Florida State University)wind stress data aredecomposed into a vortical and a divergent component with each of which to force the model oceanin the context of a two-layer tropical Pacific model.Evidence suggests that for the seasonalvariation the ocean forcing does not produce a realistic cold tongue using either of the componentsand the tongue will not be effectively improved in its intensity and pattern even if the componentsare doubled or halved:the utilization of climatic mean wind stress(no decomposition is done of thewind stress)that contains its seasonal variation will lead to a realistic SST distribution on which isimposed,separately,the interannual anomalies of each of the components so as to get the SSTApattern:under the action of the interannual anomaly of the vortical(divergent)component therearises qnite intense SSTA oscillation marked by noticeable ENSO periods(feeble SSTA withhigher oscillation frequency for obscure ENSO periods),thereby illustrating that the roles of thetwo components differ from each other in the genesis of SST variation on a seasonal and aninterannual basis such that a realistic cold tongue pattern follows under the joint effects on themodel ocean of the two components of wind stress while rational E1 Nino/La Nina phenomenaresult under the forcing of an anomalous wind stress vortical component.Moreover,the divergentcomponent is innegligible in generating a mean climatic condition of the ocean sector but of lessimportance compared to the vortical component in ENSO development.     

NUMERICAL STUDY ON THE ROLE OF VORTICAL AND DIVERGENT COMPONENTS OF WIND STRESS IN ENSO CYCLE*

The 1960-1991 monthly mean FSU (Florida State University)wind stress data are decomposed into a vortical and a divergent component with each of which to force the model ocean in the context of a two-layer tropical Pacific model.Evidence suggests that for the seasonal variation the ocean forcing does not produce a realistic cold tongue using either of the components and the tongue will not be effectively improved in its intensity and pattern even if the components are doubled or halved:the utilization of climatic mean wind stress(no decomposition is done of the wind stress)that contains its seasonal variation will lead to a realistic SST distribution on which is imposed,separately,the interannual anomalies of each of the components so as to get the SSTA pattern:under the action of the interannual anomaly of the vortical(divergent)component there arises qnite intense SSTA oscillation marked by noticeable ENSO periods(feeble SSTA with higher oscillation frequency for obscure ENSO periods),thereby illustrating that the roles of the two components differ from each other in the genesis of SST variation on a seasonal and an interannual basis such that a realistic cold tongue pattern follows under the joint effects on the model ocean of the two components of wind stress while rational E1 Nino/La Nina phenomena result under the forcing of an anomalous wind stress vortical component.Moreover,the divergent component is innegligible in generating a mean climatic condition of the ocean sector but of less importance compared to the vortical component in ENSO development.     

NUMERICAL EXPERIMENT OF THE INFLUENCES OF HEAT AND WIND STRESS ON THE EQUATORIAL OCEAN CIRCULATION

A time-dependent linear model on the equatorial beta plane is developed in this paper.Its verticalstructure consists of two active layers with equal density and temperature above the thermocline and aquasi-stationary layer with constant density below the thermocline.The results of nurnericat experiments show that the direct influence of heat on the equatorial ocean ismuch smaller than that of wind stress.Nevertheless,through the tropical ocean-atmosphere interaction,the change of wind stress resulting from the thermal forcing may set a determinant effect on the equilibriumand anomalous development of the ocean-almosphere circulation.     

NUMERICAL EXPERIMENT OF THE INFLUENCES OF HEAT AND WIND STRESS ON THE EQUATORIAL OCEAN CIRCULATION*

A time-dependent linear model on the equatorial beta plane is developed in this paper.Its vertical structure consists of two active layers with equal density and temperature above the thermocline and a quasi-stationary layer with constant density below the thermocline.The results of nurnericat experiments show that the direct influence of heat on the equatorial ocean is much smaller than that of wind stress.Nevertheless,through the tropical ocean-atmosphere interaction,the change of wind stress resulting from the thermal forcing may set a determinant effect on the equilibrium and anomalous development of the ocean-almosphere circulation.     

ON WESTERLY WIND BURSTS IN EQUATORIAL WESTERN PACIFIC BEFORE AND DURING THE ONSET AND INITIAL DEVELOPMENT PHASES OF ENSO

By means of NCEP/NCAR reanalysis dataset,the origins of westerly wind anomalies at lowlevel over equatorial western Pacific Ocean before and during the onset and initial developmentphase of ENSO are explored.Evidences show that westerly anomalies in the equatorial westernPacific(140—180°E)are characterized by two remarkable enhancements in the spring and summerof the year when El Nine emerges.The enhancements are not only.to some extem.due to theeastward propagation of low-level westerlies in equatorial Indian Ocean.but also predominantlyresulting from Ihe intense convergence of the meridional wind from both hemispheres.Thelatitudinal convergence leads to the local intensification of zonal pressure gradient so as to cause thereinforcement and bursts of westerly wind over warm pool.Besides,by virtue of the effect ofearth rotation,the northeasterlies(southeasterlies)from the Northern(Southern)Hemisphereturn into northwesterlies(southwesterlies)progressively in the near-equatorial zone.whichdirectly strengthens the westerly velocity.Comparing the contributions of the meridional windfrom both hemispheres to westerly wind bursts,is seems that southeasterlies from the SouthernHemisphere are much stronger and more stable than northwesterlies of Northern Hemisphere.It isevident that the southeasterlies to the east of Australia originate from the southern mid-and highlatitudes and are in close association with the Southern Oscillation.     

THE ROLE OF MERIDIONAL WIND STRESS IN THE TROPICAL UNSTABLE AIR-SEA INTERACTION

1INTRODUCTIONAsshowninobservationalfacts,theevolutionofElNi駉displaysastheamplitudeexpansionandmigrationofanomalousdisturbancesinair-seacouplingsystems.Theoreticaladdressofthephenomenonhasbeenattemptedfromtheaspectofcouplingdynamics.Theresultsshowthattheair-seainteractionsystemincludesakindofunstablemode,whichispropagatingindirectionsdeterminedbyfactorsgoverningSSTchanges.Withanair-seacouplingmodel,Lau[1]wasamongtheearliestpeoplewhodiscoveredunstablestationarywavemodesintheair-seaintera…     

ENSO及其年代际异常对全球及亚洲季风降水影响的数值研究

根据诊断分析结果,利用ＬＡＧＳ改进的Ｌ９Ｒ１５气候谱模式,设计了３个数值试验,讨论了不同的年代际背景下ＥＮＳＯ异常对全球降水,特别是对亚洲季风降水的影响。试验结果表明,在年代际的冷、暖背景下,当出现ＥＮＳＯ事件时,降水响应的异常场在ＥＮＳＯ的不同发展阶段上,表现显著不同。出现这种差异的物理过程可以用与垂直环流相联系的势函数的变化来表示。暖背景下,当ＥＮＳＯ处于发展时期,比冷背景下更容易出现强烈反Ｗａｌｋｅｒ的环流,但在ＥＮＳＯ处于衰减期更容易产生强烈的Ｗａｌｋｅｒ环流,这就意味着暖背景时的ＥＮＳＯ异常对大气影响的幅度更大。     

偏北大风的数值预报释用方法研究

本文利用欧洲中心中期数值预报结果，从不同侧面选取因子，建立了日最大平均风速的四种统计预报方程，在此基础上设计了几种集成方法对预报结果进行集成，结果表明，我们设计的最大值－阀值综合集成法取得了很好的效果，特别是2－3天的大风预报准确度较高。