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1.
锋生作用对2011年梅汛期湖北暴雨的影响 总被引：3，自引：1，他引：2
利用常规气象资料、湖北人工气象站和自动气象监测站雨量资料、NCEP再分析0.5°×0.5°等资料,对锋生函数在2011年6月中上旬梅雨期三次暴雨过程中的作用进行了诊断分析。结果表明:(1)2011年湖北梅雨在单阻型环流场形成和维持的过程中,先后出现了三种不同特征的暴雨过程。三次过程均在中层出现锋生。(2)中层锋生主要由垂直锋生造成,有利于对流不稳定的发生。低层锋生主要由水平锋生造成,有利于水汽输送和辐合抬升。当中层和低层均有锋生,且中层为垂直锋生、低层为水平锋生时,有利于降雨强度的加强。(3)先出现中层锋生后出现低层锋生可能为短时降雨,先出现低层锋生后出现中层锋生可能为长历时降雨。(4)低层的垂直锋消与水平锋生完全抵消说明低层水平辐合不够强,且对流稳定,不利于强降雨的发生。 相似文献
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Analytical solution for two-dimensional thermal plume updraft velocity is obtained under the assumption of a uniform temperature excess inside the plume. In this way, the thermal plume motion is modeled in both mixed layer and entrainment zone. Also, a semi-analytical solution is obtained using an empirical model for the plume temperature excess in the mixed layer. In addition, an analytical model for entrainment zone thickness is obtained by computing the overshoot distance of the modeled plumes, and a semi-analytical model by using the empirical model for plume temperature. By using a nonlinear profile for the lapse rate in the surface layer based on the Monin–Obukhov similarity theory, our model predicts that the characteristics of the surface layer plays an important role in the structure of the entrainment zone. Finally, our solutions for plume velocity allow us to consider the effect of the lateral entrainment on the plume excess temperature and velocity in the convective boundary layer. It is shown that the lateral entrainment has an important role on the plume dynamics and the solutions in the zero entrainment limit offer large overestimated values for the plume velocity, which also result in overestimated values of the entrainment zone thickness. 相似文献
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Presented is a review of quantitative characteristics of atmospheric frontogenesis that describe it as the process of variations of the vector of the horizontal temperature gradient (both in value and in direction) in an individual particle. The frontogenesis that strives for recovering the thermal wind balance disturbed in the case of inhomogeneous advection, generates vertical circulation which is both thermally direct (warm air ascends relative to cold air) and thermally opposite (upward motions in the cold air). Given are the expressions for computing frontogenesis using the data on temperature, pressure, and wind. Used is the resolution of the frontogenetic vector function into components along the isoline of potential temperature both on and across the constant-pressure surface. The first component describes the change in the temperature gradient vector due to the rotation of isotherms (rotational frontogenesis), and the second component, the variations of the absolute value of the gradient (scalar frontogenesis). Quantitative characteristics of frontogenesis are efficient diagnostic parameters both for understanding weather processes and weather forecast specification and for the verification and enhancement of numerical models. 相似文献
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作者的目的是分析地形对由于热力差异所引起的局地锋生现象和地转适应过程的影响．为此，分别用零位涡流和均匀位涡流来近似代替实际大气，并借助位涡、绝对动量、位温的守恒关系，就地形对适应锋生和适应过程中能量转换等问题进行了简单讨论。初始位温扰动的水平分布及其相对于地形的位置对适应锋生有重要影响。当初始热力扰动主要位于地形迎风坡山脚时，地形不利于锋面形成，这时要形成锋面不连续，初始位温梯度的水平变化必须非常显著；当初始热力扰动主要位于山顶附近时，地形促进流体运动的辐合，有利于锋面不连续的形成，这时即使初始位温梯度的水平变化不是很大，也可能会形成锋面；当初始热力扰动主要位于背风坡时，地形是否有利于锋面不连续的形成取决于流体的层结情况，如果流体的基本层结很弱，地形促进锋面不连续的形成，反之，地形不利于锋面不连续的形成，这种差异主要是由于在这两种情况下，地形引起的下沉增温效应的强弱是不同的。另外，地形对地转适应过程中动能和位能之间的能量转换率也有影响，与没有地形的情况相比，当初始热力差异显著区位于迎风坡时，能量转换率减小，当不平衡场位于背风坡时，能量转换率增加，原因是在迎风坡流体要克服重力作功，在背风坡重力对流体作正功。 相似文献
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Summary The problem of along-stream ageostrophic frontogenesis is studied by employing a numerical model at meso-alpha and meso-beta scales in simulations of the downstream circulations over the Front Range of the Rocky Mountains. Three-dimensional real data simulations at these two scales of motion are used to diagnose the transition from semigeostrophic cross-stream frontogenesis accompanying a propagating baroclinic upper-level jet streak to midtropospheric along-stream ageostrophic frontogenesis. This along-stream ageostrophic frontogenesis results from the perturbation of the jet streak by the Rocky Mountain range. The case study represents an example of internal wave dynamics which are forced by the drag of the Rocky Mountains on a strong jet streak in the presence of a low-level inversion.The simulation results indicate that, unlike semi-geostrophic frontogenesis, a front (which is alligned perpendicular to the axis of the jet stream) may form when significant adiabatic heating occurs within a stratified shear flow over horizontal length scales shorter than the Rossby radius of deformation. The mechanism responsible for the frontogenesis is the growth of the divergent along-stream wind velocity component which becomes coupled to the front's along-stream pressure gradient force. This nonlinear interaction produces hydrostatic mesoscale frontogenesis as follows: 1) vertical wind shear in the along-stream plane strengthens resulting in the increasingly nonuniform vertical variation of horizontal temperature advection as the ageostrophic wind component grows in magnitude downstream of the meso-scale terrain-induced adiabatic heating, 2) increasing along-stream differential vertical motions (i.e., along-stream thermally indirect circulation with warm air sinking to the west and cold air rising to the east) tilt the vertical gradient of isentropes into the horizontal as the vertical temperature gradient increases due to the previous process in proximity to horizontal gradients in the along-stream component of the ageostrophic wind, 3) as tilting motions act to increase the along-stream horizontal temperature gradient, the along-stream confluence acts to nonuniformly increase the along-stream frontal temperature gradient which increases the along-stream pressure gradient force resulting in further accelerations, ageostrophy, and frontal steepening as part of a scale contraction process.The evolution of the aforementioned processes results in the three-dimensional hydrostatic frontogenesis accompanying the overturning of isentropic surfaces. These adjustments act to turn air parcels to the right of the southwesterly geostrophic wind vector at successively lower atmospheric levels as the scale contraction continues. This simulated along-stream front is verified from diagnostic analysis of the profiler-derived temperature and wind fields.With 17 Figures 相似文献
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利用常规气象资料、自动气象站降水资料和NCEP再分析1°×1°等资料,对福建2017年6月初一次强降水过程进行多尺度分析。结果表明:(1)冷空气与暖湿气流相互作用形成持续性暴雨,中尺度系统的活动导致短时暴雨。(2)较大的风暴相对螺旋度,低层的正涡度和中低层的上升运动有利于中尺度对流系统(MCS)的发展和维持;强烈的热力不稳定和较强的垂直风切变是中尺度对流发展的环境特征。(3)强的整层水汽通量和水汽辐合为暴雨区提供水汽来源和水汽条件。(4)锋生的大小和位置对降水的强度和落区有很好的指示作用;低层以水平锋生为主,中层以垂直锋生为主,有利于成片暴雨的发生。(5)中尺度系统对天气尺度的水汽辐合和边界层对流不稳定条件有增幅作用;上下两支次级环流的上升支叠加,有利于低层不稳定能量的释放,促进中尺度系统的发展。 相似文献
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利用地面常规观测、NCEP/NCAR0.25°×0.25°再分析及风廓线雷达等资料，诊断分析了2018年10月17—18日乌鲁木齐极端暴雪天气过程的锋面特征。结果表明：在欧洲高压脊衰退，中亚长波槽分段东移的背景下，天山北坡强烈锋生并持续近30小时，此次锋生是热力和动力共同作用的，天山附近锋面呈带状准垂直分布，动力锋生激发的次级环流使垂直运动维持发展，为大暴雪提供动力条件； 400～600 hPa西南和地面～850 hpa西北路径输送的水汽，在600～800 hPa强烈辐合，为乌鲁木齐暴雪提供充沛水汽。风廓线雷达监测资料水平风向风速的垂直变化、Cn2能够反映锋生和水汽的演变特征，也从观测事实上证实了锋面对动力抬升及水汽辐合的重要作用。 相似文献
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采用T213产品中的物理量资料和天气图、卫星云图和雷达回波资料,对2007年7月1日江汉平原和鄂东的大暴雨天气过程的环流背景及其动力、热力、水汽条件进行了综合分析。结果表明：乌山低槽分裂出的冷空气东移,在华北东北部形成气旋波,其后部冷空气南下与副热带高压北上携带的暖湿气流相对峙所形成的湿度锋锋生和低层低涡、切变线是造成本次大暴雨天气过程的主要天气系统。有利强降水的各物理量场配合是降水云团迅速发展加强的有利条件。有能量锋区配合的θse高能区和K指数≥39℃的区域是有利大暴雨产生的区域。 相似文献
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Climatological Characteristics of Frontogenesis and Related Circulations over East China in June and July 总被引：1，自引：0，他引：1 
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下载免费PDF全文 Based on daily precipitation data from 212 stations in East China and NCEP/NCAR daily global final analysis data in June and July from 2000 to 2010, the climatological characteristics of frontogenesis and related circulations have been analyzed. The results demonstrate that frontogenesis function distributes nonuniformly in East China. The different terms of the kinematic frontogenesis show different intensities and distributions of frontogenesis. The strongest frontogenesis integrated from different kinematic frontogenesis terms is observed in the Jianghuai area. Frontogenesis events are separated into four types as per the different shear and convergence types of horizontal wind along the strong frontogenesis band at 850 hPa. The four types include the warm shear type, cold shear type (with two subtypes), west wind convergence type, and east wind convergence type. The events in different frontogenesis types occur with different frequencies over the past decade. The warm shear type occurs most frequently. Different types of frontogenesis have distinctive horizontal and vertical structures. Strong frontogenesis is featured with 340-K contour of θse parallel to the frontal zone in the vertical. Varied large-scale circulation patterns manifested in shifted location and strength of cyclone or anticyclone, wind convergence, as well as vertical circulation structure are associated with different types of frontogenesis. Moreover, a strong positive correlation between frontogenesis and precipitation is found, i.e., the stronger the frontogenesis, the more precipitation there is. Daily precipitation related to the warm shear type frontogenesis is the largest, and often occurs inside the frontal zone with the same orientation with the strong frontogenesis belt. The second largest daily precipitation occurs with the cold shear type frontogenesis, and related rainfall is usually observed to the south of the frontal zone, with the rain belt extending northeastward. Precipitation related to the west wind convergence type frontogenesis is the third largest, occurring mostly in the south of the frontal zone. 相似文献
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A generalized frontogenesis function and its application 总被引：3，自引：0，他引：3
With the definition of generalized potential temperature, a new generalized frontogenesis function, which is expressed as the Lagrangian change rate of the magnitude of the horizontal generalized potential temperature gradient, is derived. Such a frontogenesis function is more appropriate for a real moist atmosphere because it can reflect frontogenesis processes, in which the atmosphere in a frontal zone is typically characterized by neither completely dry nor uniform saturation. Furthermore, by derivation, the expression of generalized frontogenesis function includes both temperature and humidity gradients, which is different from and superior to the traditional frontogenesis function in moist processes, which also uses equivalent potential temperature. Diagnostic studies of real cases are performed and show that the generalized frontogenesis function in non- uniformly saturated moist atmosphere indeed provides a useful tool for frontogenesis, compared to using the traditional frontogenesis function. The new frontogenesis function can be used in situations involving either a strong temperature or moisture gradient and is closely correlated with precipitation. 相似文献
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基于中国东南沿海冬季强降水的统计分析,采用EOF、REOF、North检验等方法对2011—2016年冬季(12、1、2月)欧洲中期天气预报中心降水资料进行分类,选取位于内陆的第1、第4 REOF模态,对该两模态的降水样本进行合成分析,合成的降水中心与东南沿海福建的多年统计暴雨中心吻合。与强降水相配合,1 000 hPa上有自北向南的渐近线型辐合气流,并伴有锋区,从而形成天气尺度渐近线型锋生辐合线,强降水位于辐合轴线左侧气旋式风切变处。这是一类以前未曾受到关注和讨论的东南沿海地区冬季暴雨系统。利用客观判定方法和建立系统坐标系,以确认并诊断该系统的结构。在冷干少雨、低层盛行偏北风的冬季,此类系统兼有锋区热力抬升与辐合气流动力抬升,在雨区形成旺盛的上升运动;同时,通过辐合线正交风分量将邻近的海面水汽汇集到降水区,与中高层副高边缘偏南气流相向而行,构成较为深厚的交汇式水汽输送层;通过非绝热加热,形成深厚的热力对流不稳定,并通过干区向湿气团下楔入,形成下干上湿的湿动力不稳定,以及假相当位温随高度增加而递减,形成上暖湿、下冷干的对流不稳定层。因此,该系统对冬季强降水的发生发展及落区具有重要影响。通过WRF模式的模拟结果探讨环境热力机制的影响,结果显示,凝结潜热加热可影响辐合线的辐合位置和强度、锋生区的位置及强度,进而影响系统的活跃程度。中层潜热加热抑制平流感热冷却进入暖气团,维持降雨区的热力不稳定和降水强度。渐近线型锋生辐合线有利于东南沿海冬季大范围降水出现暴雨,其中凝结潜热释放具有重要贡献。 相似文献
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The adaptive wavelet collocation method(AWCM)is a variable grid technology for solving partial differential equations(PDEs)with high singularities.Based on interpolating wavelets,the AWCM adapts the grid so that a higher resolution is automatically attributed to domain regions with high singularities. Accuracy problems with the AWCM have been reported in the literature,and in this paper problems of effciency with the AWCM are discussed in detail through a simple one-dimensional(1D)nonlinear advection equation whose analytic solution is easily obtained.A simple and effcient implementation of the AWCM is investigated.Through studying the maximum errors at the moment of frontogenesis of the 1D nonlinear advection equation with different initial values and a comparison with the finite difference method(FDM) on a uniform grid,the AWCM shows good potential for modeling the front effciently.The AWCM is also applied to a two-dimensional(2D)unbalanced frontogenesis model in its first attempt at numerical simulation of a meteorological front.Some important characteristics about the model are revealed by the new scheme. 相似文献
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利用中国气象局热带气旋年鉴、FY-2D（0.1°×0.1°）云顶亮温、逐时自动气象站降雨量、常规观测资料和NCEP/NCAR再分析资料,运用锋生函数对台风“麦德姆”（Matmo,1410）影响辽东半岛和山东半岛期间的降水特征进行了诊断分析。结果表明：1）Matmo影响辽东半岛和山东半岛期间,其低压环流与西风带高空槽相互作用,在其西侧和东北侧分别有冷锋和暖锋锋生,两条锋带均向东移。强锋生区首先在低层生成,随后尽管高空锋区向下延伸,但并未与低层冷锋重合,低层冷锋锋生强度减弱。2）山东半岛和辽东半岛的降水均发生在台风低压环流的锋生过程中,但山东半岛的降水明显多于辽东半岛。这与锋生强度密切相关,辽东半岛的锋生强度和垂直运动较山东半岛明显偏弱。3）强降水与台风环流内冷、暖平流活动密切相关,冷暖平流交汇之处对强降水有较好的示踪作用。山东半岛始终处于冷暖平流交汇处,其西侧斜压不稳定加强,上升运动发展,强降水出现在冷锋带上暖平流区内;而辽东半岛由冷平流转为暖平流时,对流运动向其东北方向发展,强降水位于辽东半岛东北部。 相似文献
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利用常规气象观测资料、NCEP FNL分析资料（水平分辨率为1°×1°,时间分辨率为6 h）,对2013年7月21-22日和2014年7月8-9日两次陕北暴雨过程成因进行热力动力诊断,结果表明:两次陕北暴雨与高低空急流关系密切,暴雨带位于低空急流左侧的水汽辐合区,“0721”过程低空急流更强,在高低空急流耦合的强上升运动区（延安）出现大暴雨。降水前期,两次过程大气均存在对流不稳定,切变线触发对流,产生强降水,而其释放的凝结潜热加热形成中低层大气的热力不连续面,湿斜压性及锋生增强,造成整层饱和大气的抬升,维持强降水。“0721”过程前期对流降水的潜热释放更大,由此反馈的低空急流及锋生更强,出现大暴雨天气。广义对流涡度矢量垂直分量很好地描述了两次暴雨过程高低空急流耦合作用以及凝结潜热释放增强的锋生作用,其变化趋势能够反映降水的发展和减弱过程。暴雨出现在湿热力平流参数垂直积分大值中心及南侧的高梯度区,大值中心出现后约6 h会产生强降水,这对于强降水落区的预报有一定指示意义。 相似文献
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利用ERA-Interim 0.125°×0.125°高分辨率逐6小时再分析数据,选取昆明准静止锋2008年1~2月长时间维持过程诊断分析了锋生函数及其各分项在锋面生消过程中的作用与贡献,并结合2016年1月20~27日锋面增强西进过程和1979年1月14~20日锋面减弱东退过程进行了比较分析。结果表明:（1）非绝热加热项对锋面生消作用较小,但存在显著的日变化。在辐射作用下,非绝热加热项日间表现为锋消,夜间为锋生。（2）西移冷气团在被高原大地形抬升过程中存在局地地形迫使冷气团下沉的情况,并导致垂直运动倾斜项表现为锋生。由于地形固定不变,局地锋生形成次级锋生带。次级锋生带与昆明准静止锋的形成、维持和东西摆动有密切的联系。（3）辐合辐散项和水平形变项是锋生函数变化的主要贡献项,其中水平形变项中的切变变形作用以锋生为主,而伸缩变形项在纬向产生锋生,在经向产生锋消。 相似文献
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A new frontogenesis function is developed and analyzed on the basis of a local change rate of the absolute horizontal gradient of the resultant deformation. Different from the traditional frontogenesis function, the newly defined deformation frontogenesis is derived from the viewpoint of dynamics rather than thermodynamics. Thus, it is more intuitive for the study of frontogenesis because the compaction of isolines of both temperature and moisture can be directly induced by the change of a flow field. This new frontogenesis function is particularly useful for studying the mei-yu front in China because mei-yu rainbands typically consist of a much stronger moisture gradient than temperature gradient, and involve large deformation flow. An analysis of real mei-yu frontal rainfall events indicates that the deformation frontogenesis function works remarkably well, producing a clearer mei-yu front than the traditional frontogenesis function based on a measure of the potential temperature gradient. More importantly, the deformation frontogenesis shows close correlation with the subsequent(6 h later) precipitation pattern and covers the rainband well, bearing significance for the prognosis or even prediction of future precipitation. 相似文献
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冷锋雨带中湿物理过程与非绝热锋生的相互作用 总被引：3，自引：0，他引：3
利用包含冰相微物理过程参数化方案的三维非静力中尺度／云模式（ARPS）模拟了与冷锋有关的冷锋雨带（NCFR）结构，着重分析了锋面云系发展演变的主要特征。模拟结果表明，锋面云系是由位于锋面前沿处的锋面次级环流的上升运动激发的；锋面强度与冷锋云（雨）带中的潜热释放之间的正反馈引起的持续非绝热锋生是锋面以及冷锋雨带得以长时间维持的主要物理机制。进一步分析表明，锋区两侧位温梯度的增加是与沿着冷锋表面的倾斜上升运动引起的云水及水汽的再分布密切相关的，即在冷气团中由云水蒸发发冷却形成冷池，而在暖气团中由水汽凝结以及雨滴冻结等形成暖池，这种冷／暖池在冷／暖气团上的叠加是引起非绝热锋生的关键。 相似文献