“10.7”安庆特大暴雨及中尺度低涡结构的数值模拟与分析

采用常规气象观测、地面加密降水资料、FY-2E卫星逐时T_BB资料以及WRFV3.3高分辨率模式输出资料,对2010年7月12—13日安庆罕见特大暴雨过程的中尺度对流系统的发生发展、结构特征及形成原因进行了综合分析。WRFV3.3中尺度非静力模式很好地模拟了此次切变线暴雨的雨带走向、几个暴雨中心的位置和强度,以及中尺度对流系统的整个发展过程。分析结果表明:此次特大暴雨是在高层200 hPa强大的南亚高压稳定少动,中层500 hPa的短波槽的生成、转向和发展与副高的维持,低层的700 hPa和850 hPa中尺度低涡、切变线以及地面梅雨锋扰动的共同作用下造成的;700 hPa低涡、切变线以及沿切变线相继生成和强烈发展的β中尺度对流系统是这次特大暴雨的直接制造者。细网格模拟结果揭示,安庆特大暴雨与850 hPa上的β中尺度对流系统(MβCS)的生成和强烈发展直接相关。该MβCS具有明显的动力—热力结构特征,显示:强上升运动与饱和气柱的耦合,强散度柱与强涡柱的耦合发展,强上升运动与位势不稳定的耦合发展,湿静力不稳定与湿对称不稳定共存。     

“10.7”安庆特大暴雨及中尺度低涡结构的数值模拟与分析

采用常规气象观测、地面加密降水资料、FY-2E卫星逐时TBB资料以及WRFV3.3高分辨率模式输出资料,对2010年7月12-13日安庆罕见特大暴雨过程的中尺度对流系统的发生发展、结构特征及形成原因进行了综合分析.WRFV3.3中尺度非静力模式很好地模拟了此次切变线暴雨的雨带走向、几个暴雨中心的位置和强度,以及中尺度对...     

一次华南暴雨过程的数值模拟———中尺度对流系统形成发展机制

2008年6月11-13日在华南地区出现了特大暴雨,这主要是由一系列中尺度对流系统(MCS)的相继生成,合并和强烈发展导致的.该研究利用新一代中尺度数值模式WRF对此次暴雨过程进行数值模拟,重点研究此次强降水过程中MCS发生、发展和演变过程及其相关物理机制.在MCS的生成过程中,由于西南涡的存在导致MCS始终处于正涡度环境中,正涡度导致的低层辐合与大气静力不稳定都是重要的MCS启动机制,这两者的共同作用有利于MCS的生成与加强.MCS形成后,在强垂直切变的环境中,倾斜抬升机制发生作用,更进一步加强了环境涡度,形成有利的正反馈过程,造成MCS迅速发展.这些加强的MCS和大尺度环境流场相互作用,造成了它们的合并.在MCS的分裂过程中,马氏力起着重要作用.     

Formation and evolution of mesoscale convective systems that brought the heavy rainfall over Seoul on September 21, 2010

An investigation has been carried out using observational data and a numerical model to explain the formation and development of heavy precipitation systems on September 21, 2010. These systems were responsible for heavy rainfall over the middle Korean peninsula, with a maximum 24-h rainfall amount greater than 290 mm in the Seoul metropolitan area. Both observational analysis and a numerical simulation indicate that an important starting condition for this heavy rainfall event is the presence of a pressure trough over the Shandong peninsula and the Yellow Sea. Convective cells formed in the early morning over this trough area, grew into larger systems as they moved eastward, and induced the formation of a meso low over the Yellow Sea around 0000 UTC on September 21, 2010. A stationary front with significant vertical circulation developed in response to the deformation of flow associated with the meso low. In the meantime, multicell-type convective systems continuously developed and moved along the front. These storms developed further and produced heavy rainfall over the middle Korean peninsula, which includes the Seoul metropolitan area. According to observations, the band structure appeared to change after 0700 UTC as a narrow convection band developed over the sea, upstream of the existing band of multicell storms. Numerical simulation showed a similar transition. However, it failed to reproduce the stationary behavior of the observed band.     

2005年6月华南特大连续性暴雨的环境条件和中尺度扰动分析

利用常规观测站、地面加密站资料、卫星红外云图TBB和NCEP再分析资料,对2005年6月19—24日发生在广东的特大连续性暴雨过程进行了分析。天气分析表明：高空南亚高压前部的强辐散场,500 hPa河套阻塞高压以及低层低涡切变线横卧在江淮一带、低空急流源源不断地向华南输送暖湿气流的这种大尺度环流形势和相应的大范围动力热力及水汽条件,决定了暴雨的多发时期和持续性;区域暴雨多发期内5次强降水的具体发生和间歇,则与暴雨区大气动力、热力及水汽条件的5个 α 中尺度时间变化与震荡密切联系并受其影响;暴雨区动力条件的α中尺度时间变化与特定的大尺度环流背景下高低空急流的演变有密切的关系。降水的中尺度特征分析表明：暴雨过程中5场暴雨的发展和间歇对应5个 α 中尺度系统的发展和减弱,暴雨是由19个 β 中尺度系统直接造成19个 β 中尺度大雨团形成。进一步分析表明：强降水主要发生在地面静止锋和锋前暖区的中尺度切变线（或中尺度辐合线）和中尺度涡旋或中尺度辐合中心附近,中尺度涡旋内的降水是由飑线上 γ 中尺度对流单体形成的“列车效应”产生的,而中尺度切变线附近的降水则是飑线的发展合并加强产生的。发生在冷式切变线附近的强降水移动速度较快,发生在暖式切变线附近的强降水移动缓慢,发生在辐合中心的强降水在原地发展达最强后随辐合中心转为切变线减弱或直接在原地减弱消失而结束。     

Impact of 4DVAR assimilation of rainfall data on the simulation of mesoscale precipitation systems in a mei-yu heavy rainfall event

The multi-scale weather systems associated with a mei-yu front and the corresponding heavy precipitation during a particular heavy rainfall event that occurred on 4 5 July 2003 in east China were successfully simulated through rainfall assimilation using the PSU/NCAR non-hydrostatic, mesoscale, numerical model （MM5） and its four-dimensional, variational, data assimilation （4DVAR） system. For this case, the improvement of the process via the 4DVAR rainfall assimilation into the simulation of mesoscale precipitation systems is investigated. With the rainfall assimilation, the convection is triggered at the right location and time, and the evolution and spatial distribution of the mesoscale convective systems （MCSs） are also more correctly simulated. Through the interactions between MCSs and the weather systems at different scales, including the low-level jet and mei-yu front, the simulation of the entire mei-yu weather system is significantly improved, both during the data assimilation window and the subsequent 12-h period. The results suggest that the rainfall assimilation first provides positive impact at the convective scale and the influences are then propagated upscale to the meso- and sub-synoptic scales.
Through a set of sensitive experiments designed to evaluate the impact of different initial variables on the simulation of mei-yu heavy rainfall, it was found that the moisture field and meridional wind had the strongest effect during the convection initialization stage, however, after the convection was fully triggered, all of the variables at the initial condition seemed to have comparable importance.     

Life cycle of mesoscale convective systems

Radar observations of the evolution and hierarchy of Cb clouds in different regions of the Earth are generalized to present the concept of a life cycle of a mesoscale convective system; during the life cycle, the separate Cb clouds develop into hierarchic coordinated mesoscale clusters, which recurrently originate and are localized in fixed places in the system which moves as a unit. The rising dominant clusters generate quasi-periodic oscillations of maximum intensity and wavelike space structure of the precipitation field. The methodological principles of the concept are used for objective classification of precipitation systems based on morphological and evolutional features. They can be used in techniques of very-short-range forecasting of hazardous convective weather.     

大尺度环境中中尺度对流系统生成的数值模拟试验

对1983年6月11日20时(北京时)实测资料进行低通滤波处理,取其大尺度部分作为初值,用七层原始方程模式对江淮气旋内中尺度对流系统的生成过程进行数值模拟试验.结果表明,从大尺度背景场出发,可以模拟出中尺度对流系统的生成.在西南低空急流十分潮湿的情况下,中尺度对流系统可以在江淮气旋暖区、低空急流大风速中心的前部、位势稳定度倾向维持负值的地区生成和发展.它的动力、热力结构,降水分布,以及发生、发展过程等,都与暖季(3—9月)在美国中部频繁出现的中尺度对流复合体(MCC)十分相似.     

NUMERICAL SIMULATION OF THE GENERATION OF MESOSCALE CONVECTTVE SYSTEMS IN LARGE－SCALE ENVIRONMENT

The generation of mesoscale convective systems is simulated by a 7-level primitive equation model. The large-scale parts of observed, data at 1200 Z June 11, 1983, which are obtained by low-pass filter, are used as the initial data. The results show that the generation of mesoscale convective systems can be simulated from fields of meteorological variables on the large-scale background. When the low-level south-west jet stream is very moist, mesoscale convective systems can develop ahead of the wind speed maximum in the warm sector of Jiang-Huai (Changjiang-Huaihe Rivers) cyclone, where the potential stability tends to remain negative. Furthermore, they are similar to the mesoscale convective complex (MCC), which appears frequently in the central part of the United States during the warm season (March to September), in dynamical and thermal structure, distribution of precipitation and the process of generation and development.     

The structure of mesoscale convective systems in central Russia

Described is the organization of 216 summertime mesoscale convective systems (MCSs) in Moscow region. Initially, the horizontal radioecho fields corresponding to the stage of MCS reflectivity maximum were divided into 92 lines with the length of more than 200 km and 124 nonlinear MCSs. Subsequently, three types of lines were separated: lines with solid segments of reflectivity of more than 40 dBZ of ∼100 km long, discontinuous convection bands representing the combinations of linear and node-like amorphous thunderstorms, and convex or concave bow-shaped systems frequently forming the families of spirals or occlusions. The nonlinear MCSs contain circular radar cells (similar to open mesoscale cells) or small bow segments of ∼30 km; however, the most intensive storms have a propagation axis connecting the major MCSs. Finally, an objective classification of MCSs is proposed based on the quantiles of climatological distributions of various parameters describing the intensity, morphology, and kinematics of MCSs.     

中尺度强对流云系相互作用与热带气旋形成的数值模拟

本文是热带气旋形成的多尺度组合理论的续篇它以新的方法——数值模拟的结果支持了这一理论。特别是它进一步证实了“热带大气涡旋增幅效应”的存在,也进一步定量地解释了热带气旋前期低压环流的形成。     

Passive microwave and infrared structure of mesoscale convective systems

Summary The precipitation structure of mature Mesoscale Convective Systems (MCS) is examined in both the midlatitudes and the tropics using SSM/I microwave measurements, geostationary satellite observations, and ground-based radar observations. Discussion includes qualitative comparisons between midlatitude and tropical MCS cases, with particular emphasis on the delineation of convective and stratiform regions and the characterization of microwave polarization difference temperatures in the MCSs. Implications are given regarding the importance of the vertical precipitation structure on top of the atmosphere (TOA) microwave temperatures and for rain retrieval algorithms using measurements from space.Some of the principle findings include the ability of passive microwave brightness temperature measurements to distinguish stratiform and convective regions of MCSs for both tropical and midlatitude cases and over land and ocean backgrounds. Convective regions typically had low differences between the vertical and horizontal brightness temperatures while the stratiform regions have larger differences, and these differences are likely related to the spatial microphysical variations in the upper levels of the precipitation region. Several cases were found in midlatitudes and one case in the tropics where the lowest infrared (IR) brightness temperatures were displaced into the anvil region and were not colocated with the coldest microwave temperatures. Life cycle dependence of the displacement is suggested, but the SSM/I measurements with a maximum of twice daily coverage over the same location were inadequate to answer this question.With 10 Figures     

Synoptic controls of outer mesoscale convective systems with high impact rainfall in western north pacific tropical cyclones

The generality of our conceptual model of Outer Mesoscale Convective System (OMCS) formation in western North Pacific Tropical Cyclones (TCs) that was based on a case study of Typhoon Fengshen (2008) is examined with a data base of 80 OMCSs during 1999-2009. Formations of 41 “Intersection type (Itype)” OMCSs are similar to our conceptual model in that the key feature is an elongated moisture band in the northerly TC circulation that interacts with the southwest monsoon flow. Two subtypes of these I-type OMCSs are defined based on different formation locations relative to the TC center, and relative to the monsoon flow, that lead to either outward or more cyclonic propagation of the OMCSs. Twenty-five “Upstream type (U-type)” OMCSs form in a similar moisture band, but upstream of the intersection of the outer TC circulation with the monsoon flow. Another 12 “Monsoon type (Mtype)” OMCSs are different from our conceptual model as the formation locations are within the monsoon flow south to the confluence region of TC northerly circulation with the monsoon flow. In all of these OMCSs, the monsoon flow is an important contributor to their climatology and synoptic environment. Expanded conceptual models of where the threat of heavy rainfall associated with the four types of OMCSs may be expected are provided based on different OMCS formation locations relative to the TC center and different propagation vectors in a storm-relative coordinate system.     

江淮流域一种中间尺度暴雨系统的研究

通过一次江淮流域暴雨天气过程的分析,发现在对流层低层存在一种中间尺度扰动。它形成于对流层低层的冷锋锋区上,其流场的气旋性环流特征和结构在600—900米高度上最明显。它是产生江淮流域暴雨的主要天气系统之一。6小时雨量可达15—35毫米,一次扰动过程的总降水量约100—120毫米,水汽辐合主要集中在900米—700毫巴层。扰动的时间尺度为1—2天,计算结果表明,这类扰动的发生、发展与对流层低层锋区斜压性的位能释放有较好的关系。     

The role of the convective “trigger function” in numerical forecasts of mesoscale convective systems

Summary Three-dimensional numerical model simulations of a mesoscale convective system are performed to evaluate the sensitivity of the simulations to differences in the convective trigger function. The Penn State/NCAR mesoscale model with the Kain-Fritsch convective parameterization scheme is used as the modeling system for the study. All simulations are performed on the June 10–11, 1985 squall line from the OK PRE-STORM field experiment. Individual simulations differ only in their specification of the trigger function within the Kain-Fritsch scheme. Comparison of results from 12 hour simulations indicates that the position, timing, and intensity of convective activity and mesoscale features vary substantially as a function of the trigger function formulation. The results suggest that the convective trigger function is an integral part of the overall convective parameterization problem, and that great care must be exercised is designing realistic trigger function formulations, especially as model resolutions approach the scale of individual convective clouds.With 7 Figures     

散度变化在中尺度对流系统分析预报中之应用

本文介绍了近年来国内外进行中尺度系统的分析和预报中,对风场的散度变化的研究和应用。提出中尺度散度扬的配置及变化与中尺度天气(如强天气和暴雨)有十分密切的关系,它往往能预示中尺度天气的出现。在此基础上,还介绍了利用散度方程某些特征项来研究未来中尺度散度扬的变化,从而达到定性地应用的目的。从近年来国内外的应用看,这种努力是成功的。     

青藏高原上中尺度对流系统(MCSs)的个例分析及其比较

对1995年7月25—28日高原上连续数日出现MCSs的现象进行了红外云图特征及其演变、大尺度环境背景场和对流有效位能的分析。可以发现，所有这些MCSs有着相似的日变化演变过程；它们的初始对流在中午由于日射加热开始活跃，之后迅速发展，这些MCSs在后下午形成，在傍晚达到最强，之后逐渐减弱。其中26日MCS最为强大，它是在单一的强大的近于圆形的高原反气旋高压背景下受强的低层热力强迫和条件不稳定的驱动而发生的。这些发生条件都与高原本身的热力作用紧密相关，所以它的发生发展主要与高原特有的较为纯粹的热力因子相联系。28日MCS是另一个很强的MCS，它明显地受到中纬度西风槽的斜压区的影响，这二个很强的MCS有着不同的发展机制和显著不同的表现特征。     

线状中尺度对流系统的多普勒雷达统计特征分析

利用济南CINRAD/SA新一代多普勒天气雷达资料,统计分析了2004—2015年约15万km2区域内发生的148个线状中尺度对流系统（linear mesoscale convective systems,简称LMCSs）的多普勒雷达回波特征。主要分析了LMCSs的年和月分布、典型尺度、典型回波强度的统计特征以及初始回波出现时间、位置、LMCSs持续时间、演变过程回波合并特征、移动速度和方向、发展后期回波演变特征、组织类型等。LMCSs存在明显的年际变化,不同年份之间有很大的差别,而每年的6月和7月是LMCSs的高发期;80%的LMCSs是大于50 km的中-β尺度,20%属于中-α尺度,成熟期97.3% LMCSs的最大回波强度在55～70 dBz间;10—22时之间易开始形成LMCSs,14—16时是峰值,凌晨不易形成LMCSs,而LMCSs持续时间在2～18 h之间,6～8 h是峰值;一半的LMCSs在演变过程出现回波合并,合并过程可以分为与孤立对流单体合并、与对流回波群合并和与对流回波带合并三类;地形对LMCSs的触发有重要影响,太行山脉、鲁中山区的北麓和西麓容易触发形成LMCSs。这些研究为认识LMCSs发生、演变、减弱各阶段的特征,进一步提高对LMCSs的实时监测、短时预警水平提供了基础。