爆发性气旋的锋生位涡反演诊断

本文采用基于埃特尔位涡反演诊断和锋生函数诊断的锋生位涡反演诊断方法,对一次发生在西太平洋地区的爆发性气旋过程进行了诊断分析和机制研究。本文主要从锋生演变的角度,定量诊断了与对流层顶折迭现象相联系的高层位涡扰动,由凝结潜热释放造成的中层位涡扰动,与低层锋区扰动相联系的低层位涡扰动以及以低层水平辐合辐散为主要成份的非平衡风场在气旋发生发展的不同阶段所起的作用和影响,并对以上各物理过程相互作用,造成气旋爆发性发展的机制进行了分析讨论。     

凝结潜热释放对温带气旋相对涡度倾向的影响

潜热释放的作用在温带气旋的研究中一直是研究的重点。江苏省气象台沈阳等以一个产生极端降水的温带气旋为研究对象,基于全型涡度方程,计算了凝结潜热释放对气旋相对涡度倾向的贡献。结果表明,对流凝结潜热加热率最大可达稳定凝结潜热加热率的40倍。两类潜热加热中心均位于700 hPa以上,加热率垂直梯度在对流层低层为正,因而在加热中心下方形成正涡源中心。对流凝结潜热垂直梯度引发的涡度倾向比稳定凝结潜热高出1个数量级。虽然总的凝结潜热水平梯度引发的涡度倾向可以贡献气旋涡度实际增长值的65%,但对流凝结潜热垂直梯度的贡献高达其2倍。凝结潜热释放不仅能够直接引发涡度倾向,亦可通过改变位温梯度,进一步造成涡度倾向。     

海上快速发展气旋的动力诊断分析

应用等熵位涡收支方程对发生于西北太平洋日本东海附近的爆发性气旋进行了位涡及位涡收支诊断分析.发现爆发性气旋不同于普通气旋发展机制, 主要是由于平流层底位涡异常对对流层扰动产生较集中凝结加热, 使上下系统耦合打通的结果.从位涡收支来看, 气旋爆发性发展伴随着对流层顶上空有强的涡度平流作用, 而对流层中层存在着较集中的大尺度凝结结构和对流天气系统.     

西北太平洋地区一次爆发性气旋的诊断分析

采用NCEP 2.5°×2.5°每6 h再分析格点资料,对1979年1月9—12日西北太平洋地区一次爆发性气旋进行了诊断分析,重点讨论了气旋爆发的天气学特征和动力因子。结果表明：爆发性气旋的发展具有明显的非地转特性,高低空急流的耦合作用、涡度平流和凝结潜热的释放是气旋爆发性发展的主要强迫因子;爆发性气旋处于高空急流之下的对流层锋区,大气的斜压性很强,斜压能量是气旋初期生成和发展动能的主要来源。     

一次入海气旋快速发展的动力和热力学特征分析

利用扩展Zwack-Okossi方程(扩展Z-O方程)对2007年3月3-5日黄、渤海海上快速发展的温带气旋进行了诊断分析。结果表明,潜热释放和暖平流在气旋发展初期起主要作用,潜热释放是气旋接近爆发性发展的最主要强迫项,这与以往研究的主要受涡度平流强迫的中国沿海温带气旋不同,说明在中国近海快速发展的一部分温带气旋主要是由潜热释放项强迫的。绝对涡度平流在气旋发展后期才成为主要强迫项。进一步利用MM5模式模拟了潜热释放的作用以及其他一些影响气旋发展的因素,海表面热通量、水汽通量以及气旋路径上的地形对这次气旋的发展有积极贡献,但作用相对潜热释放较小。由于这种在中国近海接近爆发性发展的温带气旋容易造成风暴潮,因此利用动能方程对气旋发展中期的渤海大风进行了诊断分析。结果表明,动能水平平流是动能增加的主要作用项,但动能达到最大值后渤海海域的动能主要由有效位能转换和动量下传提供。     

东海地区温带气旋爆发性发展的动力学分析

本文对东海地区两个气旋波的爆发性发展过程进行了动力学分析。结果表明:明显的对流层中下部增温、增温以及不稳定的大气层结和强高空西风急流,及其有关的次级环流的作用是气旋爆发性发展的重要条件。在气旋爆发性发展过程中,上升运动、正涡度以及高空辐散和低空辐合的散度场皆达到最强。加热场的计算也表明非绝热加热特别是凝结潜热释放也在气旋爆发时刻达到最强,最大加热区位于气旋的东北象限内。这时涡动动能的增加十分显著,它主要是由涡动有效位能向涡动动能的转换造成,这说明气旋的爆发性发展是与斜压发展密切有关。     

一次东海气旋爆发性发展数值模拟

在2006年6月1日发生在东海的爆发性气旋的天气学分析基础上,进行数值模拟,以进一步认识其爆发性发展的物理机制。结果表明:这次东海气旋的地面系统来自台湾岛附近的海上倒槽,在浙北沿海遇到高空比较深厚的低槽,大尺度高空槽通过槽前正涡度输送和槽前后冷暖平流对斜压不稳定的加强作用为气旋发展和维持提供有利的环境。同时,高空急流也通过其出口区的辐散和暖平流为气旋发展和维持提供有利的环境。中低层在舟山海域的强涡度平流的抬升作用产生降水,并通过水汽凝结引起潜热释放,进一步造成地面气旋系统的发展,此时气旋和降水形成正反馈机制。潜热释放被高空槽前斜压不稳定和急流出口区右侧辐散共同引起的上升运动激发后,对气旋的发展起着重要作用。     

2014年11月上旬西北太平洋一次极端强度爆发气旋的数值模拟和分片位涡反演分析

基于NCEP 6 h一次,0.5°（纬度）×0.5°（经度）水平分辨率的GFS（Global Forecasting System）再分析数据,利用数值模式WRF（Weather Research and Forecasting）,对2014年11月上旬西北太平洋一次极端强度的爆发气旋事件进行了模拟。在成功复制爆发气旋主要特征的基础上,较详细的分析了本次爆发气旋快速发展的有利环境条件,并利用分片位涡反演的方法,对此次爆发气旋的快速发展过程进行了研究,主要结论如下:（1）本次爆发气旋的爆发性发展阶段维持了约27 h,其最大加深率约为3.98 Bergeron（气旋加深率单位）,最低中心气压约为919.2 hPa。（2）爆发气旋的快速发展与对流层高层高空急流对热量的输送,对流层中层西风带短波槽槽前暖平流和正涡度平流的有利准地转强迫,以及对流层低层暖锋伴随的暖平流过程密切相关。（3）分片位涡反演的结果表明,对流层顶皱褶对应的平流层大值位涡下传和降水凝结潜热过程造成的正位涡异常是本次爆发气旋快速发展的主导因子,而对流层低层的斜压过程贡献相对较小。在气旋爆发期的前期和强盛期,降水凝结潜热释放是爆发气旋发展的最重要因子,而在爆发期后期,随着降水的减弱和爆发气旋的东北向移动,对流层顶皱褶作用所造成的正位涡异常成为维持气旋快速发展的最有利因子。     

位涡扰动与气旋的发展

通过对1991－07－05T08－07－06－T20江淮流域的一次气旋发生发展过程的分析，讨论了在气旋发展的不同阶段高低层位涡场分布及垂直结构的演变特征，并从气旋发展过程中的凝结潜热释放着手，研究了高低层位涡场之间的联系。结果表明，潜热的释放将促使高层的高位涡向下传输，导致低层气旋加深发展，并进而讨论了江淮气旋发展的一种可能机制。     

台风暴雨相当位涡诊断分析

位势涡度作为热力学与动力学相结合的物理量,能更有效地显示出暴雨系统的一些特点,国内外气象学者曾用位涡来分析诸如龙卷、冰雹等强对流天气,杨大升曾用位涡成功地研究过印度季风的爆发问题,并将位涡应用于我国的暴雨诊断分析上,但暴雨过程不可能是干绝热过程,将有大量的凝结潜热释放,而潜热释放对天气系统的发生发展起着重要的反馈作用,所以将位涡应用于暴雨诊断时还应考虑水汽凝结潜热的作用。为了弥补位涡的局限性,本文从Ertel广义位涡方程出发导出了相当位涡的     

Development mechanisms of an explosive cyclone over East Sea on 3–4 April 2012

The development mechanisms of the explosive cyclone that occurred during 3–4 April 2012 over East Sea (Sea of Japan) are examined through numerical simulation and sensitivity experiments using the Weather and Research Forecasting (WRF) model. The characteristics of this explosive cyclone are different from typical cyclonic features observed in this region, including its intensity, deepening rate, and formation time. Numerical simulation, reanalysis data, upper and surface weather charts, and satellite data indicate that the strong baroclinic instability and temperature advection associated with upper-level cut-off low and the interaction of potential vorticity (PV) anomalies between the lower- and upper-level are essential to explosive cyclogenesis.The sensitivity experiments of the explosive cyclone show that latent heat release (LHR) is an important factor in explosive cyclogenesis. The intensification, extent, and movement speed of the cyclone are amplified by LHR as well as the formation of an upper-level cut-off low. The role of LHR is primary important in the generation and evolution of the cyclone. Especially, the LHR contributes to roughly 50% of decrease in sea level pressure (SLP) and 50% of the central cyclone’s low-level PV generation in initial stage. During a 48-h simulation, the contributions of the LHR, surface heat flux, and their interaction on the decrease of SLP of the cyclone are found to be 40.6, −8.2, and 10.5%, respectively. These results reveal that the explosive cyclone has larger deepening rates than OJ cyclones, and develops with a large amount of LHR near the cyclone center.     

Numerical simulations on the explosive cyclogenesis over the kuroshio current

In this paper, the Pennsylvania State University-NCAR Mesoscale Model (MM4) is used to investigate the explosive oceanic cyclone of 14-15 March 1988 over the warm Kuroshio Current. A series of numerical simulations on this cyclogenesis indicates that the favorable weather condi-tions and strong baroclinity in the low- and middle-level are essential to its explosive development. The explosive cyclogenesis occurred over a wide range of sea surface temperatures (SST’s), which was then characterized by strong baroclinity, the low-level jet (LLJ) was initially formed under the favorable atmospheric circulation and then this LLJ advected the moisture and heat northward for the explosive development of the cyclone, the LLJ played an important role in the process of cyclogenesis. Sensitivity experiments show that the latent heating was a key factor to explosive cyclogenesis, the latent heating deepened the short-wave trough, which resulted in the rapid intensification of the cyclone; while in the explosive intensification stage and continuous de-velopment stage, there was less contribution of local surface processes for the explosion of the cy?clone.     

2018年一次温带气旋入海爆发性增强时期的集合预报对比分析

基于实况观测资料、欧洲中期天气预报中心(European Centre for Medium-Range Forecast, ECMWF)0.5°（纬度）×0.5°（经度）水平分辨率的再分析数据和集合预报数据,对2018年2月一次入海爆发性气旋在黄海南部的爆发性增强时期的动力和热力因子进行了对比分析。根据气旋路径、强度和海面风的检验结果挑选出两组集合成员——好成员组和坏成员组。通过组间对比分析得到如下主要 结论 1）在气旋入海之后爆发性增强时,500 hPa高空槽和850 hPa中低层低涡迅速加强,同时低层和高层的西南急流均明显加大,中高层系统快速增强,上述因子均为气旋出现爆发性发展提供有利条件。2）气旋入海之后上升运动快速增强,这加剧了低层辐合与高层辐散,有利于地面降压,促使地面气旋的爆发性发展。水汽在中低层辐合后随气流上升发生凝结并释放潜热,这加强了高层辐散、低层辐合以及上升运动,促使气旋进一步爆发性发展。与此同时,对流层顶的高值位涡下传增强,低层大气斜压性受气旋上空冷暖平流的增强而增大,导致垂直稳定度减小,地面气旋性涡度增强,也有利于气旋爆发性发展。最终此次气旋快速增强并达到中等爆发性气旋的强度。3）虽然集合预报两组成员的平均场均比分析场弱,但是好成员组抓住了气旋上空中高层天气系统的快速增强过程,以及垂直运动、温度平流、水汽条件、位涡等预报因子和物理量的快速增强过程,其预报效果在气旋强度和路径等方面均显著优于坏成员组。     

The rapid growth and decay of severe cyclone JAL (2010) over the Bay of Bengal

This study investigates the life cycle of Bay of Bengal cyclone JAL, characterized by a rapid fluctuation in its intensity during 60-h interval. The cyclone JAL underwent a period of rapid intensification during 24-h from 0000 UTC 05 November to 0000 UTC 06 November 2010. It was quasi-static during subsequent 24 h followed by a 12-h period of unusually rapid decay. During the rapid cyclogenesis phase, the system intensified (by 25 kt) from deep depression (DD) to severe cyclonic storm (SCS) and weakened (by 30 kt) from SCS to DD during the 12-h period of rapid cyclolysis. European Centre for Medium Range Weather Forecasts (ECMWF) model analysis field is used to analyze the Q vectors, K index and potential vorticity (PV) to diagnose the life cycle of this unusual cyclone. The analysis reveals that the 500–700 hPa column-averaged Q-vector convergence above the surface cyclone had strengthened and very high values of the K index produced a burst of heavy precipitation during the development stage of the cyclone. The associated latent heat release produced a substantial diabatic positive PV anomaly in the lower and middle troposphere that caused rapid cyclogenesis. The rapid cyclolysis is coincident with the weakening of the upper and lower PV anomalies and the westward shearing of the upper PV from the cyclone centre. Thus, the very latent heat release that assisted the rapid development of the cyclone also played an important role in its subsequent rapid decay. ECMWF model forecast for track and intensity is also verified.     

Impact of tropical cyclone development on the instability of South Asian High and the summer monsoon onset over Bay of Bengal

This paper analyzes the evolution of the South Asian High (SAH) during and after the development of tropical cyclone Neoguri over the South China Sea (SCS) in mid-April 2008, the formation of tropical storm Nargis over the Bay of Bengal (BOB) in late April, and the Asian summer monsoon onset, as well as their interrelationships. Numerical sensitivity experiments are conducted to explore the underlying mechanism responsible for these seasonal transitions in 2008. It is demonstrated that strong latent heating related with tropical cyclone activities over the SCS can enhance the development of the SAH aloft and generate zonal asymmetric potential vorticity (PV) forcing, with positive vorticity advection to its east and negative advection to its west. Following the decay of the tropical cyclone, this asymmetric forcing leads to instability development of the SAH, presenting as a slowly westward-propagating Rossby wave accompanied by a westward shift of the high PV advection. A strong upper tropospheric divergence on the southwest of the SAH also shifts westward, while positive PV eddies are shed from the high PV advection and eventually arrives in the southern BOB. Such synoptic patterns provide favorable pumping conditions for local cyclonic vorticity to develop. The latent heating release from the cyclogenesis further intensifies the upper-layer divergence, and the lower and upper circulations become phase locked, leading to the explosive development of the tropical cyclone over the southern BOB. Consequently, a tropical storm is generated and the BOB summer monsoon commences.     

Potential Vorticity Structure and Inversion of the Cyclogenesis Over the Yangtze River and Huaihe River Valleys

In this paper, the potential vorticity structure and inversion of the cyclogenesis over the Yangtze River and Huaihe River valleys during 21 23 June 2003 are investigated with a potential vorticity （PV） framework. The cyclogenesis is manifested by a lower-tropospheric PV anomaly over the Yangtze River and Huaihe River valleys at early stages mainly due to latent heat release, which greatly affects the evolution of the associated lower-tropospheric geopotential height and wind fields as demonstrated by piecewise PV inversion. At later stages, an upper-tropospheric PV anomaly develops, resulting in the growth of ridges over the cyclone in both the upstream and downstream, which provide a favorable background field for the low-level cyclone development. But the effect of a surface thermal anomaly always impedes the development of the cyclone to different extents during this cyclogenesis. It is further demonstrated that the position and the strength of the PV anomaly are closely related to the low-level cyclone development, and the lower-tropospheric PV anomaly seems to constitute the most significant feature, for instance, contributing about 60% to the low-level jet （LLJ）.     

西北太平洋爆发性气旋的诊断分析

本文对一年中26个西北太平洋爆发性气旋形成的大尺度条件做了统计研究。结果表明:海洋上空大气层结的不稳定、高空急流出口区北侧的动力辐散,冬季副高位置偏北时其西侧的强暖平流以及中低层的强斜压区等都是气旋急剧发展的有利因素。 另外,本文利用完全的ω-方程和Sawyer-Eliassen次级环流方程对1983年1月6—9日发生在西北太平洋上的一次爆发性气旋做了诊断分析,得到:(1)大尺度加热是使气旋强烈发展的主要物理因子;积云对流加热也是重要的物理因子。(2)温度平流是使前两者起作用的先决因子,它对气旋的初期发展起了某种启动作用。     

东北太平洋一次强爆发性气旋发展的机制分析

使用FNL Analysis全球格点资料,对东北太平洋一次强爆发性气旋的特殊性进行了分析,发现气旋对其西北部低压系统的吸收合并是其爆发性发展过程中的典型特征,斜压强迫对其快速发展的作用较弱,与西北太平洋爆发性气旋的发展过程存在显著差异。同时,使用Zwack-Okossi诊断方程,从影响爆发性发展的动力和热力因子方面,对其发展机制作了深入的探讨。研究表明,正涡度平流、暖平流和非绝热加热的共同作用使气旋开始爆发性发展,由潜热释放导致的非绝热加热的贡献最大,非绝热加热是其快速发展的主导因子,其中正涡度平流贡献主要来自于中高层,暖平流的贡献主要来自于中低层和高层,而非绝热加热主要发生在中低层,这为东北太平洋爆发性气旋的发展机制提供了一个新的认识。