2018年1月北大西洋上一个具有“T”型锋面结构的超强爆发性气旋的分析

利用欧洲中期天气预报中心（ECMWF）提供的0.5°×0.5° ERA-Interim再分析资料，麦迪逊-威斯康星大学气象卫星研究所（CIMSS）提供的地球静止环境业务卫星（GOES-EAST）红外卫星云图和天气预报模式（WRF）的模拟结果，对2018年1月3—6日发生在北大西洋上的一个具有“T”型（T-bone）锋面结构的超强爆发性气旋进行分析。该爆发性气旋在较暖的湾流上空生成，沿海表面温度大值区向东北方向快速移动，生成后6 h内爆发性发展，24 h中心气压降低48.7 hPa。高空槽加深、涡度平流加强和低层较强的大气斜压性为气旋快速发展提供了有利的环流背景场。由于气旋发展迅速，低层相对涡度急剧增大，低压中心南部来自西北方向的干冷空气随气旋式环流快速向东推进，与东南暖湿气流汇合，锋生作用较强。较暖的洋面对西北冷空气的加热作用使得交汇的冷、暖空气温度梯度较小。减弱东移的冷锋与暖锋逐渐形成近似垂直的“T”型结构。用Zwack-Okossi方程诊断分析表明，非绝热加热、温度平流和正涡度平流是该爆发性气旋发展的主要影响因子。气旋初始爆发阶段，西北冷空气进入温暖的洋面，海洋对上层大气感热输送和潜热释放较强，非绝热加热对气旋快速发展有较大贡献。气旋进一步发展，“T”型锋面结构显著，温度平流净贡献较大，对气旋的发展和维持起重要作用。      

Impact of Mid- and Upper-Level Dry Air on Tropical Cyclone Genesis and Intensification: A Modeling Study of Durian (2001)

The impact of mid- and upper-level dry air, represented by low relative humidity (RH) values, on the genesis of tropical cyclone (TC) Durian (2001) in the South China Sea was investigated by a series of numerical experiments using the Weather Research and Forecasting model. The mid-level RH was lowered in different regions relative to TC Durian (2001)'s genesis location. Results suggest that the location of dry air was important to Durian (2001)'s genesis and intensification. The rapid development of the TC was accompanied by sustained near-saturated mid- and upper-level air, whereas low humidity decelerated its development. Water vapor budget analysis showed that moisture at mid and upper levels was mainly supplied by the vertical convergence of moisture flux and the divergence terms, and consumed by the condensation process. The horizontal convergence of moisture flux term supplied moisture in the air moistening process but consumed moisture in the air drying process. With a dryer mid- and upper-level environment, convective and stratiform precipitation were both inhibited. The upward mass fluxes and the diabatic heating rates associated with these two precipitation types were also suppressed. Generally, convection played the dominant role, since the impact of the stratiform process on vertical mass transportation and diabatic heating was much weaker. The vorticity budget showed that the negative vorticity convergence term, which was closely related to the inhibited convection, caused the vorticity to decrease above the lower troposphere in a dryer environment. The negative vorticity tendency is suggested to slow down the vertical coherence and the development rate of TCs.     

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.     

Contrasting the impact of dynamic data assimilation on the numerical simulations of cyclogenesis during GALEIOP 10 and IOP 1

Summary The nudging assimilation scheme described in the companion paper by Brill et al. is applied to study oceanic cyclogenesis during GALEIOP 10 on 27–28 February 1986. A 36-h control simulation statically initialized from 0000 UTC 27 February 1986 data moves the cyclone too far north and east in the 12-h period of most rapid deepening limiting the usefulness of the simulation for diagnostic study. The use of nudging to dynamically assimilate special 3-h and routine 12-h rawindsonde and dropsonde data into the model during the entire 36-h forecast period failed to deepen the cyclone as it moved northeast off the Atlantic seaboard beyond the area covered 3-h by sounding data. Subjectively analyzed mean sea-level pressures (MSLP) were included in the data base to allow the model to nudge toward 3-h surface pressure analyses extended to cover the region of cyclogenesis over the ocean. The assimilation of 3-h surface data over the ocean is insufficient to produce a realistic simulation of cyclogenesis. This result motivated the use of the nudging technique to assimilate surface pressure and upper air data over land during the 12-h pre-cyclogenetic period (i.e. dynamic initialization) and compare the subsequent 24-h simulation with one initialized statically at the same synoptic time.Dynamic initialization produced the best simulation of the occanic cyclone based upon the standard statistical scores and positions of the MSLP minima. This simulation is used to diagnose differences between cyclogenesis during GALEIOP 1 and IOP 10. Isentropic analyses and vertical cross sections are derived from the model simulations and are used to contrast the strength of the upper tropospheric forcing and the low-level static stability associated with each case. The results of the diagnostic analyses reveal that stronger surface response (based upon MSLP minima) to weaker upper-level forcing during GALEIOP 10 (compared with GALEIOP 1) was associated with differences in the lower tropospheric static stability and thermal advection patterns and their interaction with upper tropospheric features.With 19 Figures     

A Diagnostic Study of Explosive Development of Extratropical Cyclone over East Asia and West Pacific Ocean

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A CASE STUDY OF FRONTAL CYCLOGENESIS AND ITS SENSITIVITY TO COASTAL INITIAL CONDITIONS*

In this study,the predictability and physical processes leading to the rapid frontal cyclogenesis,that took place in the east coast of the U.S.during 3-4 October 1987,are examined using a nestedgrid.mesoscale model with a fine-mesh grid size of 25km.It is shown that the model reproduces reasonably well the cyclogenesis in a coastal baroclinic zone.its subsequent deepening and movement as well as the pertinent precipitation.It is found that the frontal cyclogenesis occurs in a favorable large-scale environment with pronounced thermal advection in the lower troposphere and marked potential vorticity(PV) concentration aloft associated with the tropopause depression.The transport of warm and moist air from the marine boundary layer by the low-level in-shore flow provides the necessary energy source for the observed heavy precipitation and a variety of weather phenomena reported in the cold sector.Several 24-h sensitivity simulations are performed to examine the relative importance of diabatic heating,adiabatic dynamics and various initial conditions in the frontal cyclogenesis.It is found that latent heat release,even though quite intense,accounts for only 25% of the cyclone's total deepening in this case:the weak impact seems due to the occurrence of latent heating in the cold sector and the upward lifting of the dynamical tropopause by diabatic updrafts.Vorticity budgets show that the lowlevel thermal advection dominates the incipient stage,whereas the vorticity advection determines the rapid deepening rate at the mature stage.The results reveal that the predictability of the present storm is closely related to the vertical coupling between the surface cyclone and the upper-level PV core,which is in turn determined by initial offshore perturbations in the lower troposphere.     

两例爆发性东北低压的对比诊断分析

该文选择了发展变化机制有一定差异的两例春季爆发性东北低压（分别是1983年4月25～26日气旋（简称A例）和1983年4月28～29日气旋（简称B例）），进行了对比诊断分析。结果表明:（1）非绝热加热和局地斜压不稳定对A例气旋发展来说是十分关键的因子，而空正IPV平流的显著增强及其与低层IPV分布中两个局地最大值的垂直耦合是B例气旋增强的一个重要原因；（2）两个风暴最大不同点在于非绝热加热效应在影响气旋增强的程度上有所不同。另外，B例事件中对流层中部产生的较强高空锋生可以在低压范围内导致深厚的上升运动并使高空锋向下游的正涡度平流得以加强，这对系统的发展是十分有利的。     

季风低压对台风生成影响的观测分析

选取2007年和2009年发生的4个季风低压个例, 利用FNL资料和CMORPH卫星反演的降水资料, 采用多尺度环流分析法, 对西北太平洋季风环流的多尺度特征进行了分析, 研究季风低压对台风生成的可能影响。分析发现:季风低压生成于季风槽中, 其天气尺度波列的气旋性环流中。虽然以季风槽为特点的低频环流为台风生成提供大尺度气候条件, 但是季风低压通过进一步提供较大的正相对涡度, 可以有效减小Rossby变形半径, 促进热带低压中中尺度对流系统的相互作用和合并, 有利于台风的生成。     

Growth and Decay of an Extra-Tropical Cyclone’s PV-Tower

Summary The surface low of a mature extra-tropical cyclone is often surmounted by a troposphere-spanning column of anomalously high potential vorticity (PV). In this study the growth and decay of such a PV-tower is traced for one major North Atlantic frontal-wave cyclone using the ECMWF analysis fields and adopting both Eulerian and Lagrangian frameworks. A tower’s structure and composition relates intimately to the strength, scale and structure of the associated surface cyclone. It is shown that the tower comprised a vertical superposition of three elements: (?) a quasi-seclusion of stratospheric air extruded from an upper-level trough, (ℬ) a mid-tropospheric layer of intermingled air from diverse sources, but with a substantial component originating from the system’s cold front, and (?) a low-tropospheric layer of diabatically-induced PV that was linked to and originated from flow along a bent-back warm front. An examination of the tower’s growth and decay helps identify the factors influencing the onset and rapidity of the cyclogenesis. There was first an in-phase development of a surface baroclinic wave with the precursor of element (?), and also the emergence of element (ℬ) in the form of a low-level elongated band of PV aligned along the cold front. Thereafter a short period of rapid growth was marked by the appearance of a low-level band of PV along the warm front (element ?), and it co-spiraled with and beneath the upper-level stratospheric intrusion (element ?). Demise of the tower followed a loss of amplitude of its central portion and a loss of coherency aloft. Evidence of the modulating as opposed to the dominating influence of diabatic processes upon the cyclone’s structure and strength is derived from consideration of: the tower’s durable and ephemeral potential vorticity, the PV production along the warm front, and sets of model simulations of the event that selectively suppress diabatic PV production. Received July 9, 1999 Revised December 2, 1999     

Sensitivity of Tropical Cyclone Intensity and Structure to Planetary Boundary Layer Parameterization

The advanced weather research and forecasting model is used to investigate the influence of planetary boundary layer (PBL) processes on intensity and structure of the storm Phailin (2013). Five simulations are conducted with five PBL schemes; Yonsei University (YSU), Mellor?Yamada?Nakanishi?Niino order2.5 (MYNN2), Assymetric Convective Model2 (ACM2), Medium Range Forecast (MRF), and Bougeault and Lacarrere (BouLac). The simulation duration includes the pre???intensification and rapid intensification phase of Phailin before landfall. Results indicate that during the pre???intensification phase, storm’s track and intensity are not much sensitivity to PBL but structural changes are noted. A significant sensitivity of track and intensity to PBL parameterizations are found during rapid intensification phase. BouLac and MRF produced two extremes with 39 hPa intense and 16 km compact storm for BouLac than MRF. Further analysis reveals an outward movement of air parcel just above the boundary layer which causes spin-down for YSU and MYNN2. BouLac is associated with stronger eddy diffusivity and moisture fluxes within the boundary layer and stronger cyclonic vorticity just above the boundary layer than other experiments. Stronger cyclonic vorticity above the boundary layer in BouLac favors intense updraft, facilitating more moisture transport from the boundary layer to upper layers aiding stronger secondary circulation and robustly intensifying the storm. A relatively deeper and drier inflow layer associated with weaker cyclonic vorticity just above the boundary layer reduces the moisture transport and weaken the secondary circulation for MRF than others.     

Intraseasonal modulation of tropical cyclogenesis in the western North Pacific: a case study

The temporal clustering of the western North Pacific tropical cyclogenesis and its modulation by the Madden–Julian oscillation (MJO) during the 1991 summer were examined based on the tropical cyclone best track, outgoing longwave radiation, and NCEP/NCAR reanalysis datasets. The wavelet analysis shows that convective activities around the monsoon trough in the western North Pacific possessed a distinct MJO with a period of 20–60 days. Two or more tropical cyclones were observed to form successively during each active phase of the MJO, and tropical cyclones tended to generate around the southeastern part of the maximum vorticity of the low-frequency cyclonic circulation during the developing and peak stages of the active MJO phase. But tropical cyclogenesis scarcely occurred during inactive MJO phases. Thus the MJO was a major agent in modulating repeated development of tropical cyclones in the western North Pacific during the 1991 summer. The MJO in circulation was characterized by a huge anomalous cyclone (anticyclone) in the lower troposphere existing alternately over the western North Pacific, leading to an enhanced (weakened) monsoon trough. An examination of the meridional gradient of absolute vorticity associated with the zonal flow indicates that the zonal flow in the monsoon trough region satisfied the necessary conditions for barotropic instability, with both zonal flow and the meridional gradient of absolute vorticity varying on the similar MJO timescale. The intraseasonal oscillation of such an unstable zonal flow might thus be an important mechanism for temporal clustering of tropical cyclogenesis in the western North Pacific. The barotropic conversion could provide a major energy source for the formation and growth of tropical cyclones in the western North Pacific during active MJO phases, with the eddy kinetic energy generation being dominated by both terms of eddies interacting with zonal and meridional gradients of the basic zonal flow.     

用Zwack-Okossi方程对一次爆发性气旋的诊断分析

利用ＥＣＭＷＦ资料作初始场,ＭＭ４模式输出的结果和Ｚｗ ａｃｋ－ Ｏｋｏｓｓｉ方程作诊断工具,对１９８１年１２月２０～２１日生成在西北太平洋的一次爆发性气旋进行了数值试验和诊断分析。得到：气旋的爆发性发展主要是由正涡度平流和非地转场激发,其中涡度平流对气旋发展贡献最大,温度平流的影响则较小,两者主要是在对流层高层起作用,而非地转场则在对流层低层起主要作用。由水汽造成的非绝热加热对本次爆发性气旋的生成影响不大,积云对流潜热的反馈作用更小。另外次天气尺度系统对爆发性气旋形成贡献较小     

西风带高空槽对登陆我国变性热带气旋的影响及其机理研究

应用日本气象厅1979~2008年的热带气旋资料以及日本25年 (JRA-25) 再分析资料, 本文首先对登陆我国变性加强和变性减弱的两类热带气旋进行了合成对比分析, 发现热带气旋变性后的强度变化与相应的西风带高空槽的强弱有很好的对应关系。然后, 我们选取了2004年登陆我国的热带气旋Haima为研究对象, 通过中尺度模式模拟再现了其登陆后变性演变过程, 采用片段位涡反演方法改变了模式初始高空槽的强度, 研究了高空槽强度的变化对Haima变性过程的影响。研究表明: (1) 高空槽加强 (减弱) 后, Haima移速明显加快 (减慢), 此外深 (浅) 槽对应的Haima变性加强过程中心气压降幅较大 (小); (2) 不同强度的高空槽与Haima相互作用的过程中, 深槽对应的高空急流范围较大, 强度更强, 相应的高空强辐散有利于Haima明显的再发展; (3) 另外深槽对应着较强的高层正位涡带, 正位涡向下伸展诱发低层Haima正位涡明显增长, 从而导致低层锋区的强烈发展和低层气旋的明显加强。     

ANALYSIS OF A CASE OF EAST ASIA COASTAL CYCLOGENESIS*

The evolution of an explosive cyclone off the East Asia coast in March 1979 is described.A shortwave trough in the southern branch of upper-level westerlies initiated the incipient cyclone.Later,a polar trough in the north amplified and became in phase with the southern shortwave to form a major trough.This major trough was responsible for the rapid intensification of the surface cyclone.In the early development stage,warm and moist air was transported northward to the developing area by a strong low-level jet.The ageostrophic wind associated with the low-level jet contributed to the frontogenesis,creating a favorable low-level environment for the rapid deepening.A low-level positive potential vorticity anomaly was created prior to the onset of rapid deepening.It was a result of frontal cloud condensation.The cyclone intensified rapidly when stratospheric air with high potential vorticity penetrated to the mid-troposphere.The rapid deepening took place at a location under the left-exit region of an amplifying jet streak behind the major trough and the right-entrance region of another anticyclonically-curved subtropical jet streak in a quasi-stationary ridge overJapan.Due to the blocking effect of the Tibetan Plateau,two shortwave disturbances were observed in the upper-level westerlies on the north and south sides of the Plateau.The southern disturbance initiated the incipient surface cyclone,while the amplifying northern disturbance was responsible for the rapid deepening.Thus,the evolution of the explosive cyclone in this case can be regarded as consecutive Petterssen's "type-B" cyclogenesis in two separate stages.     

西北太平洋热带气旋变性阶段强度变化的比较研究

选取西北太平洋上两个生命史中发生变性的热带气旋Yagi和Francisco,前者变性后有一个24小时的再增强过程,而后者则继续减弱直至消亡。利用日本气象厅提供的热带气旋资料和美国环境预报中心(NCEP)提供的FNL全球分析资料,对比分析两个TC在变性阶段的形势场,发现两者在高低层的环境场均具有明显的差异:Yagi在变性阶段其高空槽较强且在低层有一个与中纬度原先存在的温带气旋合并的过程;而Francisco在变性阶段其高空槽较弱,且变性后自行消亡。另外探讨了导致Yagi变性增强的原因,结果表明:(1)Yagi变性阶段与高空槽前的急流相互作用时,高空急流入口区左侧和出口区右侧的次级环流将产生高空辐散低空辐合的趋势,有利于低层TC低压的发展。同时,当Yagi在穿越急流的过程当中,垂直风切变的增加将导致斜压不稳定增强,低层锋区强烈发展,锋区内的斜压能量可能向TC动能转化,从而使得Yagi发展增强;(2)高空槽所对应的高层湿位涡下传可使得低层正涡度增长,从而在低层诱生出气旋性环流,有利于Yagi变性后重新发展;(3)Yagi与中纬度原先存在的温带气旋发生合并,温带气旋所带来的较高纬度冷空气的入侵增强了低层的水平温度梯度,使得低层锋区强烈发展,从Yagi以一个锋面气旋的形式而再度发展,促使其变性后进一步增强。而这些特征都是Francisco所不具备的。     

Structure and evolution of a tropopause fold during GALE IOP-1: An eta model study

Summary A fine-mesh regional model simulation of upper-level cyclogenesis is carried out to examine the structure and evolution of the accompanying tropopause fold and its relationship to the surface and upper-level cyclones. The initial state for the simulation, conducted using the 80-km, 16-level version of the National Meteorological Center Eta model, uses the Level III-b gridded dataset for 1200 UTC, 18 January 1986, during the First Intensive Observing Period (IOP-1) of the Genesis of Atlantic Lows Experiment (GALE) project.Results are presented from a 48 hour integration of the model. The emphasis is on the examination of the synoptic scale evolution and structure of the upper-level cyclone and tropopause fold, both of which were successfully simulated in the model. The potential vorticity structure associated with a propagating jet-streak displayed distinctive structure, with its tilt reversing as the jet-streak moved around the base of an amplifying upper-level trough. In addition, the model simulates the intrusion of dry, stratospheric air containing high potential vorticity anomalies into the lower troposphere as well as subsidence warming when the folding of the tropopause occurs. the model also predicts upper-level frontogenesis as a result of a thermally indirect secondary circulation in the exit region of the jet-streak. The success of the model simulation is most likely the result of comprehensive physics and the fine grid resolution employed and, more importantly, the excellent distribution of subsynoptic scale initial data during the GALE project.With 16 Figures     

季风槽中热带气旋生成初期扰动的扰动动能收支分析

热带气旋总是发生在天气尺度扰动中,本文利用NCEP/NCAR提供的FNL资料,选取了2004年8月11日—9月10日期间季风槽中5个热带气旋生成初期扰动,通过计算动能收支分析这些初期扰动的发展。其中4个热带气旋都是生成在向西北方向传播的天气尺度波列的气旋性环流中,气旋性环流可以和呈东北—西南方向倾斜西传的MRG波的逆时针环流耦合。动能收支计算表明,初期扰动动能在热带气旋生成前12~72 h不断增加,扰动位势通量的辐合对扰动动能增长起了主要作用。在季风槽东端的合流区时,能量聚集项有重要作用,随着扰动移入季风槽内,低频纬向风切变项成为能量增加的一个重要来源。Sarika生成于季风槽西撤阶段,非线性作用项对扰动发展起了关键作用。     

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.     

Sensitivity of hurricane intensity forecasts to physical initialization

Summary Intensity forecasts of a hurricane are shown to be quite sensitive to the initial meso-convective scale precipitation distributions. These are included within the data assimilation using a physical initialization that was developed at Florida State University. We show a case study of a hurricane forecast where the inclusion of the observed precipitation did provide reasonable intensity forecasts. Further experimentation with the inclusion or exclusion of individual meso-convective rainfall elements, around and over the storm, shows that the intensity forecasts were quite sensitive to these initial rainfall distributions. The exclusion of initial rain in the inner rain area of a hurricane leads to a much reduced intensity forecast, whereas that impact is less if the rainfall of an outer rain band was initially excluded.Intensity forecasts of hurricanes may be sensitive to a number of factors such as sea surface temperature anomalies, presence or absence of concentric eye walls, potential vorticity interactions in the upper troposphere and other environmental factors.This paper is a sequel to a recent study, Krishnamurti et al., 1997, on the prediction of hurricane OPAL of 1995 that was a category III storm over the Gulf of Mexico. In that study we showed successful forecasts of the storm intensity from the inclusion of observed rainfall distributions within physical initialization. In that paper we examined the issues of diabatic potential vorticity and the angular momentum in order to diagnose the storm intensity. All of the terms of the complete Ertel potential vorticity equation were evaluated and it was concluded that the diabatic contributions to the potential vorticity were quite important for the diagnosis of the storm's intensity. The present paper addresses some sensitivity issues related to the individual mesoconvective precipitating elements.With 4 Figures     

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。