登陆热带气旋维持的次天气尺度环流特征

971 1 (Winnie)和 94 0 6 (Tim)是 2个在中国登陆后长久维持 (2～ 3d)并产生严重降水的热带气旋。在深入内陆过程中 ,Winnie变性并再次加强为一个温带气旋 ,Tim则衰减消亡。采用移动坐标以及云顶亮温 (TBB)和常规资料 ,对它们在陆上维持期间的次天气尺度环流特征及其与次天气尺度系统之间的相互作用进行对比分析和诊断。结果表明 :(1 )Winnie和Tim登陆过程中具有螺旋波状的次天气尺度云系 ,这种螺旋波结构有利于热带气旋的维持。陆上维持后期 ,Winnie的螺旋云系继续维持并有所加强 ,Tim的螺旋云系趋于零散、消亡。Winnie的螺旋波特征比Tim明显 ,因而维持更长时间 ;(2 )热带气旋次天气尺度环流也具有环绕热带气旋中心的明显波动特征 ,此波动结构能否维持与热带气旋活动的天气尺度背景密切相关。在与西风槽相互作用过程中 ,Winnie的次天气尺度波动结构维持 ,而Tim的次天气尺度波动结构遭到破坏 ;(3)作为登陆后长久维持热带气旋 ,Winnie和Tim均从次天气环流中获得正涡度 ,有助于维持其气旋性环流 ,但Winnie获得的正涡度比Tim明显的大。此外 ,Winnie从次天气尺度环流中获得动能补充 ,Tim则只有次天气尺度环流对其动能的耗散。因此 ,陆上维持后期Winnie再度发展而Tim逐渐消亡     

冬季一次次天气尺度渤海气旋的动能制造

应用FGGE-Ⅲ_b资料对1979年11月24日—25日一次快速发展并造成渤海二号船翻沉事故的次天气尺度渤海气旋进行了局地动能收支分析。 气旋发展期间通过垂直气柱侧边界的动能、势能净通量是辐散的,气旋发展的能源主要依赖于动能产生项、动能转换项以及网格区域不能分辨的尺度运动作用。气旋控制期间边界层风场的增强,其外部能源主要依赖于通过侧边界的动能、势能净通量辐合,内部主要依赖于动能产生项和动能转换项。 与前人所研究过的天气尺度气旋相比较,这次气旋在发展阶段的动能产生和剩余源项[E]的数值都较大。     

一种分离暴雨过程天气尺度和次天气尺度特征的方法

作者提出利用奇异谱主分量重建技术进行气象变量场尺度分离的新构想,并设计出尺度分离的具体实施方法.使用此方法对1998年7月下旬长江流域强暴雨过程的卫星观测亮温(TBB)场进行了试验性尺度分离.结果表明,该分离技术可以将这次暴雨过程天气尺度和次天气尺度系统的基本结构清晰地分离出来.在天气尺度场上,长江流域呈现出明显的切变线上连续性对流云系的特征.在次天气尺度场上,可以清楚地显现出偶极子系统的演变特征,其活动与暴雨过程有很好的对应.     

一次次天气尺度气旋性风场扰动的特大暴雨过程

雨季对流层中下部的涡旋或地面气旋是极为重要的暴雨系统,为广大气象工作者所注意。但有时暴雨的产生既没有出现这些明显的暴雨系统,也没有天气尺度的锋面或低压相伴随。松本诚一[1]等提出了中间尺度的天气系统,指出了带有暴雨团的中、小尺度系统和中间尺度夭气系统有密切的关系,认为中间尺度天气系统是中、小尺度对流系统动量输送形成的。中、小尺度天气系统在中间尺度系统流场作用下不断发生发展和替换。     

台风异常北上时期的天气和次天气尺度环境场特征

本文利用一个空间滤波器、将台风环境场分解为天气和次天气尺度。在此基础上,对两个异常北上的台风路径（8211号台风（Cecil）和8305号台风（Abby））进行诊断分析。结果表明：台风异常北上时期出现在天气尺度环境场发生环流调查过程中,在500 hPa高度场上,台风异常北上时,表现出向着次天气尺度扰动中心传播方向移动的趋势,在天气尺度环境场作用明显减弱时期,这可能是导致台风路径异常的重要因素;同时,在动能场上,台风则表现出向着正值的次天气尺度动能制造区伸展方向移动。     

热带气旋外围环流中次天气尺度系统及其与天气尺度系统相互作用的诊断分析

本文应用带通滤波的方法,分离出热带气旋外围环流中的天气尺度和次天气尺度系统。发现热带气旋外围强降水与低层次天气尺度系统的辐合关系相当密切。文中还计算了两种尺度系统间的动能和涡度转换。得出:在650hPa以上基本上是天气尺度系统向次天气尺度系统提供动能,在650hPa以下基本上是次天气尺度系统向天气尺度系统提供动能,整层积分的结果是天气尺度系统向次天气尺度系统提供动能。在900hPa和400hPa之间的涡度转换为次天气尺度系统向天气尺度系统转换,即涡度转换的结果是使得次天气尺度系统气旋性减弱,天气尺度系统气旋性增强。900hPa以下和400hPa以上则相反。整层积分的结果是次天气尺度系统向天气尺度系统提供正涡度。      

夏季江淮气旋的结构

本文用1980年6月23—25日和8月23—25日的常规观测资料,分析两次江淮气旋的运动场和热力场的平均结构.分析中使用了活动坐标网格,对风、温度、湿度和降水等气象要素进行合成.研究指出,这类气旋的波长为2000—2500公里,水平闭合环流的尺度为100—1500公里,垂直伸展高度达7—8公里左右,气旋轴线随高度显著地向北倾斜.气旋性环流和气旋性涡度在对流层中层的700毫巴附近最强.锋区在对流层上部明显,在对流层低层反而较弱;在气旋中心附近及其北侧,在700毫巴附近及以下仅有一狭窄的冷带.强降雨区出现在低     

对我国梅雨次天气尺度系统的一些认识

为说明本文研究问题的基本观点,首先简略讨论了梅雨次天气尺度扰动的一些基本的天气动力学特点。继而综合讨论一批梅雨期暴雨个例分析的结果。对于青藏高原东侧的西南低涡和夏季江淮切变线发生的机制——特别是高原的动力和热力影响在其中起着什么样的作用;暖性低涡东移和切变线向东延伸的机制;江淮切变线维持的机制;低涡转化为江淮气旋波的天气动力过程等问题,提出一些新的探索性的意见。     

一次特大暴雨形成中天气尺度和次天气尺度系统的作用

采用中尺度数值模式MM5V2对1998年6月下旬发生在长江流域持续的暴雨过程进行分析研究。通过尺度分离与数值模拟对比试验,着重分析了暴雨过程中天气尺度与次天气尺度各物理量场的结构特征,提出本次暴雨过程形成的物理机制：天气尺度流场与水汽场为降水提供持续的远距离水汽输送通道,次天气尺度流场形成稳定的经向强辐合,为水汽的抬升与凝结提供动力条件;在有利的高、低空急流的配置下,暴雨区落在高空急流轴以南、低空急流轴以北;次天气尺度温度场下暖上冷的热力不稳定层结促进了热力不稳定的发展,促使暴雨增幅;特大暴雨发生地区上空的次天气尺度湿度的高值中心,有利于湿空气在上升运动中释放潜热,形成暴雨的反馈机制。数值试验分离模式初始场不同尺度系统信息,揭示了不同尺度系统在暴雨发生过程中的动力作用,没有中尺度系统的配合,仅有天气尺度系统信息,或只有次天气尺度系统信息,没有大尺度系统的配合,暴雨的强度及范围都将有所消减。分析及数值试验结果表明大暴雨是在天气尺度和次天气尺度系统的共同作用下才得以产生和维持的。     

夏季季风平均纬向气流的正压和斜压不稳定度

本文采用10层准地转模式对7月份水平和垂直切变的平均季风气流的正压和斜压不稳定度进行了数值研究。结果得出,其最不稳定型具有3000公里左右的波长和15米/秒左右向西的相速度,最主要的能量转换是由纬向动能变为涡动动能。最不稳定型的结构是这样的,最大振幅集结在150毫巴左右,而其最低层的振幅却小得可以忽略不计。150毫巴纬向气流的正压不稳定似乎是最不稳定型的主要激发机制,它与季风季节在对流层上层所观测到的向西传播的波动情况是相类似的。其结果进一步指出,平均季风气流的正压和斜压不稳定不能解释季风低压的形成问题,这个季风低压在低层有着最大的振幅,而在200毫巴却很少被发现。     

Effects of the East Asian summer monsoon on tropical cyclone genesis over the South China Sea on an interdecadal time scale

Tropical cyclone (TC) genesis over the South China Sea (SCS) during 1965-2004 was analyzed.The locations of TC genesis display evident seasonal changes,with the mean position of formation situated nort...     

Water vapour flux divergence over the Arabian Sea during 1987 summer monsoon using satellite data

The evaporation rates over the Arabian Sea (AS) for the summer monsoon months (June to September) of 1987 have been computed using the bulk-aerodynamic formula. The satellite derived precipitation from the INSAT-1B VHRR (Very High Resolution Radiometer) sensor operating in the wavelength 10.5–12.5 m has been used for computing the precipitation over the AS. The net water vapour flux divergence (NFD) over AS has been computed as the difference between evaporation and precipitation. The estimates being -0.02 × 10¹⁰, 2.55 × 10¹⁰, 0.70 × 10¹⁰ and 0.44 × 10¹⁰ tons/day respectively for the months June, July, August and September. The NFD over AS was found to be positively and significantly correlated with the mean monsoon rainfall along the west coast of India.     

Insolation over the Arabian Sea during the southwest monsoon

The relationship between monsoon cloud cover and incoming solar radiation in the Arabian Sea is examined utilising the available observations of daily mean total cloud amount and solar radiation collected during the summer monsoon. With these data sets, various cloud correction formulae are evaluated. For the estimation of solar radiation, the formulation of Laevastu (1960) is best, with a minimum error of -4%. A multiple polynomial regression equation based on cloud cover and noon altitude of the sun is developed for estimation of daily radiation. The error between estimated and observed radiation is -2%.     

Relationships between interannual variability in the Arabian Sea and Indian summer monsoon rainfall

Summary The interannual variability of the monthly mean upper layer thickness for the central Arabian Sea (5°N-15° N and 60° E-70° E) from a numerical model of the Indian Ocean during the period 1954–1976 is investigated in relation to Indian monsoon rainfall variability. The variability in the surface structure of the Somali Current in the western Arabian Sea is also briefly discussed. It is found that these fields show a great deal of interannual variability that is correlated with variability in Indian monsoon rainfall. Model upper layer thickness (H) is taken as a surrogate variable for thermocline depth, which is assumed to be correlated with sea surface temperature. In general, during the period 1967 to 1974, which is a period of lower than normal monsoon rainfall, the upper ocean warm water sphere is thicker (deeper thermocline which implies warmer surface water); in contrast, during the period 1954–1966, which is a period of higher than normal monsoon rainfall, the upper warm water sphere is thinner (shallower thermocline which implies cooler surface water). The filtered time series of uppper layer thickness indieates the presence of a quasi-biennial oscillation (QBO) during the wet monsoon period, but this QBO signal is conspicuously absent during the dry monsoon period.Since model H primarily responds to wind stress curl, the interannual variability of the stress curl is investigated by means of an empirical orthogonal function (EOF) analysis. The first three EOF modes represent more than 72% of the curl variance. The spatial patterns for these modes exhibit many elements of central Arabian Sea climatology. Features observed include the annual variation in the intensity of the summer monsoon ridge in the Arabian Sea and the annual zonal oscillation of the ridge during pre- and post-monsoon seasons. The time coefficients for the first EOF amplitude indicate the presence of a QBO during the wet monsoon period only, as seen in the ocean upper layer thickness.The variability in the model upper layer thickness is a passive response to variability in the wind field, or more specifically to variability in the Findlater Jet. When the winds are stronger, they drive stronger currents in the ocean and have stronger curl fields associated with them, driving stronger Ekman pumping. They transport more moisture from the southern hemisphere toward the Indian subcontinent, and they also drive a greater evaporative heat flux beneath the Findlater Jet in the Arabian Sea. It has been suggested that variability in the heat content of the Arabian Sea drives variability in Indian monsoon rainfall. The results of this study suggest that the opposite is true, that the northern Arabian Sea responds passively to variability in the monsoon system.With 10 Figures     

阿拉伯海低压形成和结构的个例分析

利用1979年夏季季风试验(Summer MONEX)得到的资料,对一个阿拉伯海低压的形成和结构进行了分析,得到了以下重要结果: (1)低压的形成和发展与低空急流的活动,尤其是其中的最大风速中心有很密切的关系。低压是在东西两支急流间的强正涡度区中形成和发展的。 (2)低压的结构有明显的不对称性。强烈的质量辐合、水汽辐合和上升运动等位于低压东侧和南侧。 (3)低压本身最强的环流位于对流层中层(700—500毫巴)。在风场、湿度场、垂直运动场等分布上有类似中层气旋之处,但在其他方面也有许多差别。 (4)低压是从一个十分暖湿的中层热带扰动发展而来。干空气的侵入可能是造成低压减弱的一个重要因子。 (5)暖心的建立是从上层向下层进行的,这说明积云对流的重要性。 (6)最后给出了低压的三维气流结构。     

Moisture transport over the Arabian Sea associated with summer rainfall over Pakistan in 1994 and 2002

In this study,we aimed to elucidate the critical role of moisture transport affecting monsoon activity in two contrasting summers over the Arabian Sea during the years 1994,a relatively wet year,and 2002,a relatively dry year.A comprehensive diagnostic evaluation and comparisons of the moisture fields were conducted;we focused on the precipitation and evaporation as well as the moisture transport and its divergence or convergence in the atmosphere.Monthly mean reanalysis data were obtained from the National Centers for Environmental Prediction(NCEP-I and-II).A detailed evaluation of the moisture budgets over Pakistan during these two years was made by calculating the latent energy flux at the surface(E P) from the divergence of the total moisture transport.Our results confirm the moisture supply over the Arabian Sea to be the major source of rainfall in Pakistan and neighboring regions.In 1994,Pakistan received more rainfall compared to 2002 during the summer monsoon.Moisture flow deepens and strengthens over Arabian Sea during the peak summer monsoon months of July and August.Our analysis shows that vertically integrated moisture transport flux have a significant role in supplying moisture to the convective centers over Pakistan and neighboring regions from the divergent regions of the Arabian Sea and the Bay of Bengal.Moreover,in 1994,a deeper vertically integrated moisture convergence progression occurred over Pakistan compared to that in 2002.Perhaps that deeper convergence resulted in a more intense moisture depression over Pakistan and also caused more rainfall in 1994 during the summer monsoon.Finally,from the water budget analysis,it has been surmised that the water budget was larger in 1994 than in 2002 during the summer monsoon.     

The effect of Arabian Sea optical properties on SST biases and the South Asian summer monsoon in a coupled GCM

This study examines the effect of seasonally varying chlorophyll on the climate of the Arabian Sea and South Asian monsoon. The effect of such seasonality on the radiative properties of the upper ocean is often a missing process in coupled general circulation models and its large amplitude in the region makes it a pertinent choice for study to determine any impact on systematic biases in the mean and seasonality of the Arabian Sea. In this study we examine the effects of incorporating a seasonal cycle in chlorophyll due to phytoplankton blooms in the UK Met Office coupled atmosphere-ocean GCM HadCM3. This is achieved by performing experiments in which the optical properties of water in the Arabian Sea—a key signal of the semi-annual cycle of phytoplankton blooms in the region—are calculated from a chlorophyll climatology derived from Sea-viewing Wide Field-of-View Sensor (SeaWiFS) data. The SeaWiFS chlorophyll is prescribed in annual mean and seasonally-varying experiments. In response to the chlorophyll bloom in late spring, biases in mixed layer depth are reduced by up to 50% and the surface is warmed, leading to increases in monsoon rainfall during the onset period. However when the monsoons are fully established in boreal winter and summer and there are strong surface winds and a deep mixed layer, biases in the mixed layer depth are reduced but the surface undergoes cooling. The seasonality of the response of SST to chlorophyll is found to depend on the relative depth of the mixed layer to that of the anomalous penetration depth of solar fluxes. Thus the inclusion of the effects of chlorophyll on radiative properties of the upper ocean acts to reduce biases in mixed layer depth and increase seasonality in SST.     

Atmospheric boundary layer sources for upper tropospheric air over the Asian summer monsoon region

利用TRAJ3D模拟亚洲夏季风区空气的边界层来源。30天后向轨迹的统计结果显示,150hPa上,源于边界层的空气主要集中在亚洲夏季风反气旋南侧的深对流区及其下风向,而不是反气旋中心;将边界层源分为海洋(20°N以南的中国南海和西太平洋)和陆地(10–30°N之间的孟加拉湾、印度、环阿拉伯海地区)分别进行考察,携带高浓度污染物的陆地边界层空气在150hPa上的集中位置与卫星观测到的CO高值中心相对应,洁净的海洋边界层空气对反气旋东南侧的高浓度污染物起到稀释作用。     

强弱南海夏季风活动及大气季节内振荡

应用ＮＣＥＰ再分析资料和中国降水资料，分析研究了对应南海强、弱夏季风的环流形势及其与之相应的中国东部的降水异常。其结果表明，由强、弱夏季风所引起的中国气候异常是完全不同（甚至反相）的。分析大气季节内振荡（ＩＳＯ）的活动还表明，对应大气强（弱）南海夏季风，南海地区 ８５０ ｈＰａ也有强（弱）大气 ＩＳＯ；而强、弱南海夏季风环流（２００ ｈＰａ和 ８５０ ｈＰａ）主要由异常的大气ＩＳＯ所激发。本研究还揭示了南海地区大气ＩＳＯ的变化往往与江淮地区大气ＩＳＯ的变化反相，例如南海地区的强（弱）大气ＩＳＯ常与江淮流域的弱（强）大气ＩＳＯ相对应。对于大气ＩＳＯ的强度，一般多表现出局地激发特征，经向传播相对较弱。     

Observations of a quasi-tropical cyclone over the Black Sea

A rare atmospheric phenomenon in the Black Sea region is described: a mesoscale cyclone with all main properties of tropical cyclones. The cyclone developed in the southwestern part of the sea and existed for about five days. General characteristics of the cyclone are presented along with its effect on thermodynamic structure of the sea upper layer.