Evolution Mechanism of a Severe Squall Line Triggered by the Coupling of a Sea Breeze Front and a Gust Front

In the present study, a severe squall line(SL) was analyzed by using intensive observational surface data and radar monitoring products. In this process, mesoscale convergence lines, such as the sea breeze front(SBF), gust front and dry line, served as the main triggering and strengthening factors. The transition from convection triggering to the formation of the initial shape was mainly affected by the convergence line of the SBF, which combined with thermal convection to form the main parts of the SL. In the later stage, the convergence line of the gust front merged with other convergence lines to form a series of strong convective cells. The SBF had good indicative significance in terms of severe convective weather warnings. The suitable conditions of heat, water vapor and vertical wind shear on the Shandong Peninsula were beneficial to the maintenance of the SL. Before SL occurrence, tropopause folding strengthened, which consequently enhanced the baroclinic property in the middle and upper troposphere. The high sensible heat flux at the surface easily produced a positive potential vorticity anomaly in the low layer, resulting in convective instability, which was conducive to the maintenance of these processes. In the system, when precipitation particles passed through the unsaturated air layer, they underwent strong evaporation, melting or sublimation, and the cooling effect formed negative buoyancy, which accelerated the sinking of the air and promoted the sustained development of the surface gale. Together with the development of lowlevel mesocyclones, the air pressure decreased rapidly, which was conducive to gale initiation.

Atypical Occlusion Process Caused by the Merger of a Sea-breeze Front and Gust Front

An atypical occlusion process that occurred in North China on 14 July 2011 is studied based on both observations and a real-data Weather Research and Forecasting （WRF） model simulation. The results show that this atypical occlusion process was significantly different from the traditional, synoptic-scale occlusion process that occurs within extratropical cyclones. It was caused by the merger of two cold-type mesoscale fronts. One of the fronts developed from the gust front of convective storms, while the other was a sea-breeze front. As the two fronts moved towards each other, the warm air between them was squeezed and separated from the surface. An atypical occluded front was formed when the two fronts merged, with the warm air forced aloft. This kind of occlusion is termed a ＂merger＂ process, different from the well-known ＂catch-up＂ and ＂wrap-up＂ processes. Moreover, local convection was found to be enhanced during the merger process, with severe convective weather produced in the merger area.

Gust Front Statistical Characteristics and Automatic Identification Algorithm for CINRAD

Gust front is a kind of meso-and micro-scale weather phenomenon that often causes serious ground wind and wind shear. This paper presents an automatic gust front identification algorithm. Totally 879 radar volume-scan samples selected from 21 gust front weather processes that occurred in China between 2009 and 2012 are examined and analyzed. Gust front echo statistical features in reflectivity, velocity, and spectrum width fields are obtained. Based on these features, an algorithm is designed to recognize gust fronts and generate output products and quantitative indices. Then, 315 samples are used to verify the algorithm and 3 typical cases are analyzed. Major conclusions include： 1） for narrow band echoes intensity is between 5 and 30 dBZ, widths are between 2 and 10 km, maximum heights are less than 4 km （89.33%are lower than 3 km）, and the lengths are between 50 and 200 km. The narrow-band echo is higher than its surrounding echo. 2） Gust fronts present a convergence line or a wind shear in the velocity field;the frontal wind speed gradually decreases when the distance increases radially outward. Spectral widths of gust fronts are large, with 87.09% exceeding 4 m s-1 . 3） Using 315 gust front volume-scan samples to test the algorithm reveals that the algorithm is highly stable and has successfully recognized 277 samples. The algorithm also works for small-scale or weak gust fronts. 4） Radar data quality has certain impact on the algorithm.

An Algorithm for Automated Identification of Gust Fronts from Doppler Radar Data

Gust fronts are weak narrow-band echoes of increased reflectivity at the background levels in the low-elevation fields of Doppler radar. An automated approach to gust front detection that relies on the image features of radar observations is presented in this paper. The algorithm is not sensitive to the variations in reflectivity values and gust front widths. The approach includes the following steps. First, a novel local binary with dual-template(LBDT) algorithm is designed as the fundamental algorithm to identify the potential areas of narrow-band echoes. Second,based on the disadvantages of the LBDT algorithm, several modifications are made, including splitting the intersecting lines, connecting the fragments, and filtering the edges and radial interference noise. Third, an optical flow method is used to determine whether a weak narrow-band echo is a gust front according to the prior knowledge that a gust front usually propagates in front of the associated generating storm. The results of experiments show that the proposed method can automatically identify gust fronts with a high probability of detection and a low false alarm rate. The automatic identification of gust fronts is potentially useful for accurate short-term weather forecasting, particularly in the forecasting of storm winds.

Observation of a Straight-Line Wind Case Caused by a Gust Front and Its Associated Fine-Scale Structures

A straight-line wind case was observed in Tianjin on 13 June 2005,which was caused by a gust front from a squall line.Mesoscale analyses based on observations from in-situ surface stations,sounding,and in-situ radar as well as fine-scale analyses based on observation tower data were performed.The mesoscale characteristics of the gust front determined its shape and fine-scale internal structures.Based on the scale and wavelet analyses,the fine-scale structures within the gust front were distinguished from the classical mesoscale structures,and such fine-scale structures were associated with the distribution of straight-line wind zones.A series of cross-frontal fine-scale circulations at the lowest levels of the gust front was discovered,which caused a relatively weak wind zone within the frontal strong wind zone.The downdraft at the rear of the head region of the gust front was more intense than in the classical model,and similar to the microburst,a series of vertical vortices propagated from the rear region to the frontal region.In addition,strong tangential fine-scale instability was detected in the frontal region.Finally,a fine-scale gust front model with straight-line wind zones is presented.

Adaptive Wind Gust and Associated Gust-factor Model for the Gust-producing Weather over the Northern South China Sea

Wind gusts are common environmental hazards that can damage buildings,bridges,aircraft,and cruise ships and interrupt electric power distribution,air traffic,waterway transport and port operations.Accurately predicting peak wind gusts in numerical models is essential for saving lives and preventing economic losses.This study investigates the climatology of peak wind gusts and their associated gust factors(GFs)using observations in the coastal and open ocean of the northern South China Sea(NSCS),where severe gust-producing weather occurs throughout the year.The stratified climatology demonstrates that the peak wind gust and GF vary with seasons and particularly with weather types.Based on the inversely proportional relationship between the GF and mean wind speed(MWS),a variety of GF models are constructed through least squares regression analysis.Peak gust speed(PGS)forecasts are obtained through the GF models by multiplying the GFs by observed wind speeds rather than forecasted wind speeds.The errors are thus entirely due to the representation of the GF models.The GF models are improved with weather-adaptive GFs,as evaluated by the stratified MWS.Nevertheless,these weather-adaptive GF models show negative bias for predicting stronger PGSs due to insufficient data representation of the extreme wind gusts.The evaluation of the above models provides insight into maximizing the performance of GF models.This study further proposes a stratified process for forecasting peak wind gusts for routine operations.

廊坊市雷暴大风多普勒雷达特征指标预警应用分析

利用北京、天津和沧州多普勒天气雷达对2010—2019年廊坊市发生的29次雷暴大风天气过程中的阵风锋、径向速度大值区、垂直累积液态水含量(VIL)≥40 kg·m^(-2)等预警指标进行验证分析,结果表明:51.9%的站次出现了阵风锋,其中61.0%的雷暴大风出现在主体回波移动前方中部到右侧;17 m·s^(-1)以上大风速区作为预警指标,预警的平均提前量达47.2 min。100%的弓形回波雷暴大风出现前上游及可能影响区域存在≥17 m·s^(-1)的大风速区,以此发布预警可提前37.1 min;71.4%的雷暴大风站点上空或10 km范围内VIL≥40 kg·m^(-2),平均预警提前量最高,达到52.7 min;依据带状回波前侧或右前侧出现阵风锋发布预警的平均提前量为60.6 min。73.7%的块状回波雷暴大风天气上游及可能影响区域有≥17 m·s^(-1)的大风速区。结合上游及可能影响区域≥17 m·s^(-1)和≥20 m·s^(-1)大风速区、阵风锋、VIL≥40 kg·m^(-2)出现位置可以提前30~60 min发布雷暴大风预警信号,且可更加精准地预测灾害性大风的落区、出现时间和强度。

冷涡影响下杭州湾一次区域性极端大风的演变和机制分析

利用常规气象探空观测、地面自动气象站逐分钟观测、风廓线雷达以及多普勒天气雷达等多源观测资料,分析了2021年4月30日傍晚到夜间浙江北部和杭州湾沿海地区一次区域性极端大风的天气特征,重点探讨了对流系统移入杭州湾后的中尺度演变特征和大风增强的原因。结果表明,此次过程是典型的多尺度相互作用的结果,在高空深厚的东北冷涡影响下,配合中层西北急流和较强的地面暖低压促使飑线后部对流系统发展,形成雷暴大风天气。对流单体在经过杭州湾水系后明显增强,其阵风锋前侧有西南暖湿入流,后部冷池发展强盛,气压涌升,叠加地面环境风场和杭州湾水面的热动力条件,从而触发不稳定能量促使单体发展。系统经过杭州湾后辐散下沉出流明显增强,将中高层的动量更快地下传至地面,对于杭州湾南部风力增强效应显著。杭州湾光滑下垫面、喇叭口等特殊地形也是造成极端大风出现的原因之一。同时,逐分钟变温相比于极大风出现时间提前了约7~10 min,对于局地极端大风监测预警有一定的指示意义。

一次阵风锋碰并作用触发短时强降水过程观测分析

对足够精细的观测资料做详尽的分析有助于澄清对流组织与增强的动力机制。本文利用机场跑道两端的分钟雨量资料、常规观测资料、加密自动站、ERA5再分析和S波段双偏振、X波段双偏振相控阵雷达资料,对2022年7月15日厦门机场出现的一次短时强降水天气进行了分析。结果表明:此次过程因阵风锋在传播过程中与地面辐合线交叉碰并而触发抬升,在500 hPa与850 hPa假相当位温差的负大值区和低层高温高湿的环境下激发出新的对流,给厦门机场带来罕见的短时强降水天气,期间分钟雨量最大达2.5 mm、跑道能见度降至400 m,两者呈反相关,但当分钟雨量大于1.6 mm时两者反相关性减弱,能见度谷值则晚于雨量峰值出现。观测分析表明,径向速度的气旋性切变与分钟雨量的变化趋势较为一致,两者有较好的对应关系。当2~5 km高度存在气旋性切变时雨量显著增加,当有两个高度层的切变强度达到2×10~(-3)s~(-1)以上时分钟雨量可达约2 mm,为本次短时强降水的组织特征。

A simulation-based study on longitudinal gust response of flexible flapping wings

Winged animals such as insects are capable of flying and surviving in an unsteady and unpredictable aerial environment.They generate and control aerodynamic forces by flapping their flexible wings.While the dynamic shape changes of their flapping wings are known to enhance the efficiency of their flight,they can also affect the stability of a flapping wing flyer under unpredictable disturbances by responding to the sudden changes of aerodynamic forces on the wing.In order to test the hypothesis,the gust response of flexible flapping wings is investigated numerically with a specific focus on the passive maintenance of aerodynamic forces by the wing flexibility.The computational model is based on a dynamic flight simulator that can incorporate the realistic morphology,the kinematics,the structural dynamics,the aerodynamics and the fluid-structure interactions of a hovering hawkmoth.The longitudinal gusts are imposed against the tethered model of a hovering hawkmoth with flexible flapping wings.It is found that the aerodynamic forces on the flapping wings are affected by the gust,because of the increase or decrease in relative wingtip velocity or kinematic angle of attack.The passive shape change of flexible wings can,however,reduce the changes in the magnitude and direction of aerodynamic forces by the gusts from various directions,except for the downward gust.Such adaptive response of the flexible structure to stabilise the attitude can be classified into the mechanical feedback,which works passively with minimal delay,and is of great importance to the design of bio-inspired flapping wings for micro-air vehicles.

Characteristics of daily extreme wind gusts on the Qinghai-Tibet Plateau, China

Severe wind is a major natural hazard and a main driver of deserdficadon on the Qinghai-Tibet Plateau. Generally, studies of Qinghai-Tibet Plateau＇s wind climatology focus on mean wind speeds and its gust speeds have been seldom investigated. Here, we used observed daily maximum gust speeds from a 95- station network over a 5-year period （2008-2012） to analyze the characteristics of extreme wind speeds and directions by fitting Weibull and Gumbel distributions. The results indicated the spatial distribution of extreme wind speeds and their direction on the Qinghai-Tibet Plateau is highly variable, with its western portion prone to greater mean speeds of extreme wind gusts than its eastern portion. Maximum extreme wind speeds of 30.9, 33.0, and 32.2 m/s were recorded at three stations along the Qinghai Tibet Railway. Severe winds occurred mostly from November to April, caused primarily by the westerly jet stream. Terrain greatly enhances the wind speeds. Our spatial analysis of wind speed data showed that the wind speeds increased exponentially with an increasing altitude. We also assessed the local wind hazard by calculating the return periods of maximum wind gusts from the observational data based on the statistical extreme value distributions of these wind speeds. Further attention should be given to those stations where the yearly maximum daily extreme wind speed increased at a rate greater than that of mean value of daily extreme wind speeds. Severe extreme wind events in these regions of the plateau are likely to become more frequent. Consequently, building structural designers working in these areas should use updated extreme wind data rather than relying on past data alone.

Operational Safety Assessment of a High-Speed Train Exposed to the Strong Gust Wind

The operational safety characteristics of trains exposed to a strong wind have caused great concern in recent years.In the present paper,the effect of the strong gust wind on a high-speed train is investigated.A typical gust wind model for any wind angle,named“Chinese hat gust wind model”,was first constructed,and an algorithm for computing the aerodynamic loads was elaborated accordingly.A vehicle system dynamic model was then set up in order to investigate the vehicle system dynamic characteristics.The assessment of the operational safety has been conducted by means of characteristic wind curves(CWC).As some of the parameters of the wind-train system were difficult to measure,we also investigated the impact of the uncertain system parameters on the CWC.Results indicate that,the descending order of the operational safety index of the vehicle for each wind angle is 90°-60°-120°-30°-150°,and the worst condition for the operational safety occurs when the wind angle reaches around 90°.According to our findings,the gust factor and aerodynamic side force coefficient have great impact on the critical wind speed.Thus,these two parameters require special attention when considering the operational safety of a railway vehicle subjected to strong gust wind.

Near ground wind characteristics during typhoon Meari:Turbulence intensities, gust factors, and peak factors

Wind data were collected during the 2011 typhoon Meari at heights of 10, 20, 30, and 40 m above the ground using a 40 m high anemometer tower in the coastal area near Shanghai Pudong International Airport. Wind speeds and directions, turbulence intensities, gust factors, and peaks were analyzed using the time records of wind speed. The results show that turbulence intensity components in longitudinal, lateral, and vertical directions decrease with mean wind speed, regardless of elevations, and the turbulence intensities are in a linear relationship with mean wind speeds. The ratios of three turbulence intensity components(i.e. Iu, Iv, Iw) at heights of 10, 20 and 40 m were calculated and equal to be 1:0.88:0.50, 1:0.84:0.57, and 1:0.9:0.49, respectively. In addition, the gust factors in three directions exhibit a reduction with increasing mean wind speed. The peak factors at different heights show a similar trend and slightly decrease with mean wind speed; average peak factors for all 10-min data from Typhoon Meari are 2.43, 2.48, and 2.47, respectively.

一次强对流过程中两种不同类型风暴导致的极端对流大风分析

利用多源观测资料,对2021年4月30日发生在黄淮地区的一次强对流过程中由不同类型风暴系统造成的极端对流大风进行了探讨。研究表明,此次强对流过程发生在东北冷涡背景下的强风垂直切变和层结不稳定环境中,地面气旋及锋面触发了初始对流,在之后近10 h的传播过程中经历了组织化发展、孤立风暴新生、发展、合并与重组等不同阶段。期间,由两种不同类型风暴产生了特征相异的对流性大风:第一阶段,以江苏淮安站为代表,苏中极端对流性大风(36.2 m/s)是由发展强烈的超级单体风暴引发下击暴流所致。对流风暴低层呈现出明显的钩状回波特征,对应深厚的具有显著气旋性旋转的中气旋,在地面极端大风临近时刻,中气旋存在同时向上和向下拉伸、水平尺度快速收缩过程。贯穿整个风暴的下沉气流位于风暴钩状回波后侧,这支强下沉气流至地面附近迅速向外辐散,伴随风暴内强反射率核快速下降,导致淮安产生时、空尺度小且空间分布显著不连续的极端大风。第二阶段,以江苏南通地区为代表,苏东南地区极端大风的发展过程涉及多尺度天气系统的相互作用。线状对流系统前部存在明显的阵风锋,造成较大范围10级以上的地面大风;南通通州湾极端大风(47.9 m/s)发生在阵风锋后侧,其形成一方面是由于线形对流风暴造成的强冷池与地面冷锋相叠加,形成更强的气压梯度,另一方面与地面中尺度气旋入海过程中的快速发展以及风暴后侧倾斜向前的下沉气流导致的高空风动量下传有关。

Modeling Technique of the Aircraft Unsteady Aerodynamics Due to the Travelling Gust

The main equations for computing the unsteady aerodynamics of the aircraft undergoing the travelling gust are derived.Research and simulation on a specific example aircraft are performed,the results indicate that the modeling technique of the aircraft unsteady aerodynamics is correct,and it can meet the requirements due to the head⁃on and tail⁃on travelling gusts.

湖北雷暴阵风锋特征及其对流触发作用分析

基于2016—2021年湖北多普勒雷达及加密自动气象站资料,对湖北雷暴阵风锋特征进行分析。结果表明:(1)湖北阵风锋主要出现在6—8月,占总数的96%,其中8月最多;一天中主要发生时段为15:00—18:00(北京时,下同),峰值在17:00;大多数阵风锋持续时间为1.5~3.0 h;产生阵风锋的母雷暴中35%为多单体雷暴,40%为多单体雷暴群,25%为飑线。(2)阵风锋主要有5个生成区域,分别为省外、鄂东北、江汉平原、鄂西北的襄阳和鄂西南的宜昌,相同区域生成的阵风锋移动方向有较好的规律性。鄂东北生成的阵风锋最多,占总数的33%。(3)不是所有母雷暴及其阵风锋都能引发地面大风,69%的母雷暴和9%的阵风锋产生的地面极大风速大于等于17.0 m·s^(-1)。在多单体和多单体雷暴群中,母雷暴的回波强度越强,母雷暴及其阵风锋产生的地面大风概率越大,阵风锋产生的地面风速强度与其回波强度、空间尺度关系不大。(4)阵风锋有较强对流触发能力,91%的阵风锋在其后部、附近和前侧触发对流单体。母雷暴与其阵风锋反馈作用不同,对流触发与阵风锋的相对位置有差别,正反馈型大多在阵风锋后部触发对流,负反馈型在阵风锋后部、附近和前侧均可触发对流,29%的触发对流回波强度大于等于55 dBZ。35%的阵风锋与周边已有雷暴合并发展形成合并型阵风锋,此型在鄂东北发生次数最多。

秦岭北麓两次下山雷暴不同演变特征分析

2018年7月26日和29日,秦岭北麓雷暴下山形成阵风锋并均在关中平原造成强对流天气,雷暴下山后强度、移动速度以及影响范围差异大,预报难度大。利用多源观测资料及ERA5再分析资料分析这两次过程(分别简称为7·26过程和7·29过程)的差异及成因。结果显示:7·26过程雷暴组织化程度高、生命史长、冷池小时最大变温为16℃,产生大范围短时强降水和雷暴大风;7·29过程以孤立普通单体的生消为主,冷池小时最大变温为8℃,仅造成秦岭沿山局地短时强降水。7·26过程发生在副热带高压西北侧,中低层暖平流发展使不稳定能量增长,关中平原上升运动及北山地形抬升为雷暴移入后发展加强提供了有利的动力条件;7·29过程发生在副热带高压南侧,关中平原以下沉运动为主,不利于雷暴移入后进一步发展加强。7·26过程阵风锋移动方向与边界层风向相反,又与风暴承载层平均风向相同,有利于对流垂直发展,对流发展过程中低层垂直风切变逐步增大,与冷池强度保持同步增长;7·29过程阵风锋移动方向和边界层风向相同,低层辐合弱,整个过程中0~3 km风矢量差始终不足5 m·s^(-1),不利于对流组织化发展。特殊地形对冷池的移动方向及强度产生了影响:7·26过程强的西南出流使冷池呈东北—西南狭长带状沿平原南边界向东北推进,冷池势力集中,移速快,强的辐合触发新对流发展;7·29过程冷池在黄土台塬地形过渡区扩散传播,东南风和西南风出流使对流分裂,冷池强度减弱,不利于新对流触发。

北京地区雷暴阵风锋触发对流新生的环境场特征分析

为了加强对雷暴阵风锋触发对流新生环境场特征的认识,利用北京地区常规探空观测资料、地面加密自动站、 S波段多普勒天气雷达及多种新型探测资料对北京地区雷暴阵风锋触发对流新生的两种典型个例的环境场特征进行分析。结果表明:(1)Ⅰ型为多条阵风锋相遇或阵风锋与其他边界层辐合线相遇,在高对流有效位能CAPE和高湿区域触发对流(即碰撞型触发)。此类型中,两条阵风锋相遇时产生了比单条阵风锋大得多的垂直速度,强烈的上升运动为对流触发提供了良好的抬升条件。(2)Ⅱ型为阵风锋移动至高CAPE区域触发对流(即非碰撞型触发)。此类型阵风锋在移动方向上与环境风有强辐合,同时,垂直于阵风锋剖面内的风分布有利于触发对流的上升气流倾向于竖直。(3)阵风锋触发对流新生的环境场中,用CAPE表示的深厚湿对流潜势普遍较未触发对流的个例高,对流抑制能量CIN低;大部分个例高层有干冷平流、低层有暖湿平流,垂直方向上的静力不稳定较强;大部分新生的对流出现在低层风向切变或风速辐合以及高CAPE地区。(4)未触发对流的个例中,环境场在垂直方向上的分布不利于对流的新生和发展,阵风锋经过的地区为辐散区或低CAPE高CIN的地区,动力和热力条件配合不理想,不利于对流触发。

2018年8月13日天津静海龙卷的雷达特征和发生条件

利用常规观测资料、地面自动气象站资料、多普勒天气雷达和风廓线雷达资料等,对2018年8月13日17:30左右发生在天津静海的EF2级龙卷天气进行分析,重点分析龙卷发生前后的环境背景条件、局地不稳定条件、触发抬升条件及雷达回波特征等。结果表明:这次龙卷天气发生在500 hPa高空槽东移、副热带高压加强西进及台风摩羯北上的过程中;龙卷发生前环境大气处于明显不稳定状态,对流有效位能为1797 J·kg^(-1)(对流抑制能量为0 J·kg^(-1))、0~6 km风矢量差约为14 m·s^(-1),且存在较低抬升凝结高度;同时龙卷发生地局地存在较大对流有效位能(最大值超过4000 J·kg^(-1))和较低抬升凝结高度,且龙卷发生前抬升凝结高度出现突降现象(最低降到897 hPa附近)。龙卷发生前后上下游两站近地层(0~1 km高度及以下)垂直风切变值均出现先迅速增大后又迅速减小的特征,且垂直风切变值的迅速减小是由上层开始并迅速向下,而0~1 km以上高度的垂直风切变值没有明显变化。多普勒天气雷达观测表明,龙卷回波单体尺度小(正负速度中心直径为2 km左右)、正负速度中心最大旋转速度为24 m·s^(-1)、垂直涡度为2.4×10^(-2)s^(-1),回波具有明显悬垂结构和有界弱回波区及龙卷涡旋(TVS)等特征,后侧低层入流也非常强,应是微超级单体龙卷。海风锋移动到本地与上游雷暴单体出流形成的阵风锋相遇发生碰撞,触发局地不稳定能量强烈释放、激发雷暴单体新生并发展为有组织的强雷暴单体,应是此次龙卷发生的直接触发条件。

一次由线状风暴和阵风锋引发的致灾大风成因

2018年6月13日,多条线状风暴和阵风锋造成山东多地出现致灾大风,基于常规、加密气象观测资料、卫星云图和多普勒天气雷达资料,对此次大风成因进行了分析。结果表明:(1)冷涡后部横槽转竖引导冷空气叠加在低层暖脊之上,850 hPa与500 hPa温差高达34.7℃,同时925~600 hPa的干层与地面至925 hPa的近饱和层相叠置,上下层大气之间温、湿差异显著,形成强热力不稳定,持续并增强的低层逆温层使不稳定能量得到积累,显著干层和低层强温度垂直递减率为夹卷和蒸发冷却过程提供了有利条件。(2)线状风暴各生命期强阵风是由内嵌其中的普通单体或超级单体下击暴流所引发。单体间下沉气流合并使地面大风的影响范围和强度有所增大。强阵风均伴随较强降雨和降雹,雨滴和冰雹的拖曳是产生下击暴流的重要原因,极大风速与5 min降水量具有正向相关性,青岛34.8 m·s^(-1)的极端大风出现时5 min降水量达19 mm。(3)山东东南部的初生对流在地面辐合线、海风锋、对流云街上被接连触发,遇阵风锋后生命史延长,得以并入到主风暴,使风暴发展壮大,而风暴中的下沉气流又驱动多股阵风锋加速向南推进,增强地面风速,阵风锋与风暴主体之间存在相互促进机制。在对流潜势较高的条件下,需关注边界层辐合线对对流的触发作用。