Typhoon-Induced Ocean Waves and Stokes Drift:A Case Study of Typhoon Mangkhut(2018)

Ocean waves and Stokes drift are generated by typhoons.This study investigated the characteristics of ocean waves and wave-induced Stokes drift and their effects during Typhoon Mangkhut using European Centre for MediumRange Weather Forecasts(ECMWF)ERA5 datasets and observational data.The results revealed that the typhoon generated intense cyclones and huge typhoon waves with a maximum wind speed of 45 m/s,a minimum pressure of955 h Pa,and a maximum significant wave height of 12 m.The Stokes drift caused by typhoon waves exceeded 0.6m/s,the Stokes depth scale exceeded 18 m,and the maximum Stokes transport reached 6 m^(2)/s.The spatial distribution of 10-m wind speed,typhoon wave height,Stokes drift,Stokes depth,and Stokes transport during the typhoon was highly correlated with the typhoon track.The distribution along the typhoon track showed significant zonal asymmetry,with greater intensity on the right side of the typhoon track than on the left side.These findings provide important insights into the impact of typhoons on ocean waves and Stokes drift,thus improving our understanding of the interactions between typhoons and the ocean environment.This study also investigated the contribution of Stokes transport to the total net transport during typhoons using Ekman-Stokes Numbers as a comparative measure.The results indicated that the ratio of Stokes transport to the total net transport reached up to 50%within the typhoon radius,while it was approximately 30%outside the radius.Strong Stokes transport induced by typhoon waves led to divergence in the transport direction,which resulted in upwelling of the lower ocean as a compensation current.Thus,Stokes transport played a crucial role in the vertical mixing of the ocean during typhoons.The findings suggested that Stokes transport should be paid more attention to,particularly in high latitude ocean regions,where strong winds can amplify its effects.

Different responses of two adjacent artificial beaches to Typhoon Hato in Zhuhai,China

Major differences in beach erosion between two neighboring artificial beaches Xiangluwan Beach(XL beach)and Meiliwan Beach(ML beach)in Zhuhai,China,were studied after Super Typhoon Hato.In this study,a fully nonlinear Boussinesq wave model(FUNWAVE)-Total Variation Diminishing(TVD)was used to distinguish the main impact factors,their relative contributions,and the hydrodynamic mechanisms underlying the different beach responses.Results show that compared to the ML beach,the main reason for the relatively weak erosion on Xiangluwan(XL)beach was the smaller beach berm height(accounting for approximately 75.9%of the erosion response).Regarding the beach with a higher berm,the stronger wave-induced undertow flow,along with the higher sediment concentration,led to a higher offshore sediment transport flux,resulting in more severe erosion relative to the beach with a smaller berm height.The second most important reason explaining the weak erosion on XL beach was the absence of seawalls(accounting for approximately 17.9%of the erosion response).Wave reflection induced by the seawall could cause higher suspended sediment concentration,resulting in a toe scouring near the seawall.The offshore submerged breakwater protected XL beach slightly(accounting for approximately 6.1%of the erosion response).Due to the higher water level induced by storm surge,most of the wave energy could penetrate through the submerged breakwater.The effect of the larger berm width of XL beach was negligible.Compared to the beach with a larger berm width,the erosion/deposition regions in the beach with a narrower berm width showed shoreward migration,without significant changes in the erosion/deposition extent.Despite of this,the larger berm width could reduce the wave energy reaching the shoreline.This study of the storm stability of artificial beaches may be applied to beach restoration design.

Probability Distribution Characteristics of Strong Nonlinear Waves Under Typhoon Conditions in the Northern South China Sea

The generation and propagation mechanism of strong nonlinear waves in the South China Sea is an essential research area. In this study, the third-generation wave model WAVEWATCH Ⅲ is employed to simulate wave fields under extreme sea states. The model, integrating the ST6 source term, is validated against observed data, demonstrating its credibility. The spatial distribution of the occurrence probability of strong nonlinear waves during typhoons is shown, and the waves in the straits and the northeastern part of the South China Sea show strong nonlinear characteristics. The high-order spectral model HOS-ocean is employed to simulate the random wave surface series beneath five different platform areas. The waves during the typhoon exhibit strong nonlinear characteristics, and freak waves exist. The space-varying probability model is established to describe the short-term probability distribution of nonlinear wave series. The exceedance probability distributions of the wave surface beneath different platform areas are compared and analyzed. The results show that with an increase in the platform area, the probability of a strong nonlinear wave beneath the platform increases.

Investigation of Maxima Assumptions in Modelling Tropical Cyclone- Induced Hazards in the South China Sea

The present study aims to examine the suitability of two commonly used assumptions that simplify modelling metoceanconditions for designing offshore wind turbines in the South China Sea (SCS). The first assumption assumes thatjoint N-year extreme wind and wave events can be independently estimated and subsequently combined. The secondone assumes peak wind and waves can be modelled as occurring simultaneously during a tropical cyclone (TC) event.To better understand the potential TC activity, a set of 10000 years synthetic TC events are generated. The wind fieldmodel and the Mike 21 spectral wave model are employed to model the TC-induced hazards. Subsequently, theeffect of the assumptions is evaluated by analyzing the peak structural response of both monopile and semisubmersibleoffshore wind turbines during TC events. The results demonstrate that the examined assumptions are generally accurate.By assessing the implications of these assumptions, valuable insights are obtained, which can inform andimprove the modelling of TC-induced hazards in the SCS region.

Limited Sea Surface Temperature Cooling Due to the Barrier Layer Promoting Super Typhoon Mangkhut(2018)

This study investigates the impact of the salinity barrier layer(BL)on the upper ocean response to Super Typhoon Mangkhut(2018)in the western North Pacific.After the passage of Mangkhut,a noticeable increase(~0.6 psu)in sea surface salinity and a weak decrease(<1℃)in sea surface temperature(SST)were observed on the right side of the typhoon track.Mangkhut-induced SST change can be divided into the three stages,corresponding to the variations in BL thickness and SST before,during,and after the passage of Mangkhut.During the pre-typhoon stage,SST slightly warmed due to the entrainment of BL warm water,which suppressed the cooling induced by surface heat fluxes and horizontal advection.During the forced stage,SST cooling was controlled by entrainment,and the preexisting BL reduced the total cooling by 0.89℃ d-1,thus significantly weakening the overall SST cooling induced by Mangkhut.During the relaxation stage,the SST cooling was primarily caused by the entrainment.Our results indicate that a preexisting BL can limit typhoon-induced SST cooling by suppressing the entrainment of cold thermocline water,which contributed to Mangkhut becoming the strongest typhoon in 2018.

Track-Pattern-Based Characteristics of Extratropical Transitioning Tropical Cyclones in the Western North Pacific

Based on the Regional Specialized Meteorological Center(RSMC)Tokyo-Typhoon Center best-track data and the NCEP-NCAR reanalysis dataset,extratropical transitioning(ET)tropical cyclones(ETCs)over the western North Pacific(WNP)during 1951–2021 are classified into six clusters using the fuzzy c-means clustering method(FCM)according to their track patterns.The characteristics of the six hard-clustered ETCs with the highest membership coefficient are shown.Most tropical cyclones(TCs)that were assigned to clusters C2,C5,and C6 made landfall over eastern Asian countries,which severely threatened these regions.Among landfalling TCs,93.2%completed their ET after landfall,whereas 39.8%of ETCs completed their transition within one day.The frequency of ETCs over the WNP has decreased in the past four decades,wherein cluster C5 demonstrated a significant decrease on both interannual and interdecadal timescales with the expansion and intensification of the western Pacific subtropical high(WPSH).This large-scale circulation pattern is favorable for C2 and causes it to become the dominant track pattern,owning to it containing the largest number of intensifying ETCs among the six clusters,a number that has increased insignificantly over the past four decades.The surface roughness variation and three-dimensional background circulation led to C5 containing the maximum number of landfalling TCs and a minimum number of intensifying ETCs.Our results will facilitate a better understanding of the spatiotemporal distributions of ET events and associated environment background fields,which will benefit the effective monitoring of these events over the WNP.

秋季登陆广东热带气旋特征变化及机制分析

基于1949—2021年中国气象局热带气旋最佳路径数据集和登陆热带气旋数据集,对秋季登陆广东热带气旋(tropical cyclone,TCs)的时空特征和可能机制进行分析,并与夏季进行对比。结果表明:近73年共76个TCs秋季登陆广东,占登陆总数的28.5%,以强台风和超强台风占主,且平均最大强度强于夏季。相比夏季,秋TCs更大比例(72.4%)生成于西北太平洋,生成经纬度偏南、偏东;秋TCs的年均破坏潜力指标(power dissipation index,PDI)可达0.4×10^(7)m^(3)·s^(-2),与夏季相当;秋TCs登陆后比夏季更快消亡,移速更慢,PDI较小。秋TCs登陆数量长期变化呈下降趋势且下降速率与夏季相当,登陆强度上升且上升速率为夏季1.8倍,移速减缓速率为夏季2.5倍,PDI下降速率明显弱于夏季。不同于夏季登陆TCs在拉尼娜年增多,秋TCs更易在厄尔尼诺年登陆广东;登陆广东秋TCs数与上一年冬春季厄尔尼诺–南方涛动(El Niño-Southern Oscillation,ENSO)指数相关系数达到0.3,并对后一年ENSO具有指示作用。秋TCs登陆频数与太平洋年代际振荡(Pacific Decadal Oscillation,PDO)指数显著相关,1977—1996和1997—2016暖冷两个位相期,相关系数分别为−0.51和0.68。对比有无秋TCs的环境场,发现南海北部海温暖异常时,其西北侧激发的气旋性引导气流利于TCs登陆广东。

Diagnostic Study of an Extreme Explosive Cyclone over the Kuroshio/Kuroshio Extension Region

Explosive cyclones(ECs)occur frequently over the Kuroshio/Kuroshio Extension region.The most rapidly intensified EC over the Kuroshio/Kuroshio Extension region during the 42 years(1979-2020)of cold seasons(October-April)was studied to reveal the variations of the key factors at different explosive-developing stages.This EC had weak low-level baroclinicity,mid-level cyclonic-vorticity advection,and strong low-level water vapor convergence at the initial explosive-developing stage.The low-level baroclinicity and mid-level cyclonic-vorticity advection increased substantially during the maximum-deepening-rate stage.The diagnostic analyses using the Zwack-Okossi equation showed that diabatic heating was the main contributor to the initial rapid intensification of this EC.The cyclonic-vorticity advection and warm-air advection enhanced rapidly in the middle and upper troposphere and contributed to the maximum rapid intensification,whereas the diabatic heating weakened slightly in the mid-low troposphere.The relative contribution of the diabatic heating decreased from the initial explosive-developing stage to the maximum-deepening-rate stage due to the enhancement of other factors(the cyclonic-vorticity advection and warm-air advection).Furthermore,the physical factors contributing to this EC varied with the explosive-developing stage.The non-key factors at the initial explosive-developing stage need attention to forecast the rapid intensification.

FY-3D卫星MWRI资料反演洋面台风降雨率

利用FY-3D卫星上搭载的微波成像仪(microwave radiation imager,MWRI)的一级亮温数据,结合二级降雨率沿轨产品,基于极化订正温度及散射指数(polarization corrected temperature and scattering index,PCT-SI)综合法,建立了升轨洋面和降轨洋面两种降雨率反演模型,并通过多个台风个例对本研究建立的两种模型进行验证。结果表明,升轨数据与降轨数据反演降雨的效果差异不大,反演的降雨分布区域比二级产品降雨区域略大;两种模型均倾向于高估降雨低值、低估降雨高值;升轨反演模型的相关系数、平均绝对误差和均方根误差分别为0.72632、2.3055mm·h^(−1)和2.7254mm·h^(−1),降轨反演模型的相关系数、平均绝对误差和均方根误差分别为0.73363、1.9079mm·h^(−1)和2.3651mm·h^(−1)。

Comprehensive Risk Assessment of Sea Level Rise and Tropical Cyclones in Dongzhaigang Mangroves,China

Mangroves play a pivotal role in tropical and subtropical coastal ecosystem,yet they are highly vulnerable to the effects of climate change,particularly the accelerated global sea level rise(SLR)and stronger tropical cyclones(TCs).However,there is a lack of research addressing future simultaneous combined impacts of the slow-onset of SLR and rapid-onset of TCs on China's mangroves.In order to develop a comprehensive risk assessment method considering the superimposed effects of these two factors and analyze risk for mangroves in Dongzhaigang,Hainan Island,China,we used observational and climate model data to assess the risks to mangroves under low,intermediate,and very high greenhouse gas(GHG)emission scenarios(such as SSP1-2.6,SSP2-4.5,and SSP5-8.5)in 2030,2050,and 2100,and compiled a risk assessment scheme for mangroves in Dongzhaigang,China.The results showed that the combined risks from SLR and TCs will continue to rise;however,SLRs will increase in intensity,and TCs will decrease.The comprehensive risk of the Dongzhaigang mangroves posed by climate change will remain low under SSP1-2.6 and SSP2-4.5 scenarios by 2030,but it will increase substantially by 2100.While under SSP5-8.5 scenario,the risks to mangroves in Dongzhaigang are projected to increase considerably by 2050,and approximately 68.8%of mangroves will be at very high risk by 2100.The risk to the Dongzhaigang mangroves is not only influenced by the hazards but also closely linked to their exposure and vulnerability.We therefore propose climate resilience developmental responses for mangroves to address the effects of climate change.This study for the combined impact of TCs and SLR on mangroves in Dongzhaigang,China can enrich the method system of mangrove risk assessment and provide references for scientific management.

Trend of Storm Surge Induced by Typical Landfall Super Typhoons During 1975–2021 in the Eastern China Sea

Climate change affects the activity of global and regional tropical cyclones(TCs).Among all TCs,typical super typhoons(STYs)are particularly devastating because they maintain their intensity when landing on the coast and thus cause casualties,economic losses,and environmental damage.Using a 3D tidal model,we reconstructed the typhoon(TY)wind field to simulate the storm surge induced by typical STYs.The TY activity was then analyzed using historical data.Results showed a downtrend of varying degrees in the annual frequency of STYs and TCs in the Western North Pacific(WNP)Basin,with a significant trend change observed for TCs from 1949 to 2021.A large difference in the interannual change in frequency was found between STYs and TCs in the WNP and Eastern China Sea(ECS).Along the coast of EC,the frequency of landfall TCs showed a weak downtrend,and the typical STYs showed reverse micro growth with peak activity in August.Zhejiang,Fujian,and Taiwan were highly vulnerable to the frontal hits of typical STYs.Affected by climate change,the average lifetime maximum intensity(LMI)locations and landfall locations of typical STYs in the ECS basin showed a significant poleward migration trend.In addition,the annual average LMI and accumulated cyclone energy showed an uptrend,indicating the increasing severity of the disaster risk.Affected by the typical STY activity in the ECS,the maximum storm surge area also showed poleward migration,and the coast of North China faced potential growth in high storm surge risks.

不同路径台风对中国近海海温的影响特征统计分析

文章基于中国气象局提供的最佳台风路径资料,基于K均值聚类分析法将2002年至2021年由西太暖池进入中国近海的台风分为3类,并依据台风路径特征将3类台风分别命名为西行路径台风、西北路径台风和转向路径台风,并使用遥感系统(remote sensing systems,REMSS)提供的海表面温度最优插值日产品和区域海气浪耦合模型(coupled ocean atmosphere wave sediment transport modeling system,COAWST)的模拟结果,对这3类台风造成的上层海洋温度的变化特征进行统计研究。结果显示,3种台风对海表面温度(sea surface temperature,SST)影响特征的不同主要体现在对SST的冷却幅度和作用时间上:转向路径台风对SST的冷却幅度最大并且作用时间最长,西北路径台风次之,而西行路径台风冷却幅度最小且作用时间最短;3种台风对混合层厚度(mixed layer thickness,MLT)与温跃层厚度(thermocline thickness,TT)影响的差异主要体现在MLT和TT的变化幅度和恢复时间上:转向路径台风的MLT和TT变化幅度最大,西北路径台风次之,西行路径台风最小。对于MLT与TT的恢复速度,西北路径台风整体上要明显快于西行路径台风和转向路径台风。

南海-西北太平洋季风槽及其与热带气旋的关系:不同再分析资料对比

利用1981—2020年中国气象局(CMA)热带气旋最佳路径数据集、CMA大气再分析资料(CMA-RA)、欧洲中期天气预报中心再分析资料(ERA5)及NCEP/NCAR再分析资料(NCEP-I),对比CMA-RA与ERA5、NCEP-I对南海-西北太平洋季风槽及其与南海热带气旋活动关系的表现能力,探讨CMA-RA的适用性。结果表明:不同资料均表征出南海和西北太平洋西段槽区低层气旋式涡旋明显、东段均匀的特征,CMA-RA和ERA5对低层涡度场描述的差异较小。两两资料间得到的季风槽强度的相关性较高,且为CMA-RA>ERA5>NCEP-I,对南海槽区的描述差异最大;对东伸点的刻画具有较高一致性,CMA-RA较ERA5和NCEP-I偏西;但对南北位置的刻画一致性较差,其中CMA-RA与ERA5的差异较小。所有资料均刻画出季风槽区中、低层强辐合、高层强辐散的结构,沿105°~160°E平均的涡度垂直剖面差异以CMA-RA与ERA5最小、CMA-RA与NCEP-I最大。CMA-RA季风槽与热带气旋频数关系最密切,ERA5次之,ERA5季风槽强度与热带气旋强度关系最密切,ERA5和CMA-RA季风槽东伸点与热带气旋强度关系较NCEP-I密切。总体来看,CMA-RA对季风槽及其与南海热带气旋活动关系的刻画具有与ERA5和NCEP-I相当的表现能力,且与ERA5的一致性高。

基于热带气旋风圈半径的海上风电场灾害预警时间估计方法研究及应用

利用2001—2019年美国国家海洋和大气管理局(NOAA)的热带气旋最佳路径数据集,统计分析了西北太平洋上影响我国沿海的热带气旋的移速、强度和风圈半径等气候特征。结果表明:8级、10级和12级热带气旋风圈半径的平均值分别为198.2 km、111.6 km、70.6 km,且风圈呈现不对称性,东北象限风圈半径最大,西南象限最小;风圈半径与强度变化呈现正相关关系;热带气旋移速、强度和风圈半径在各海域的空间分布特征明显不同,且8级和12级风圈半径随纬度变化存在显著差异。在气候特征分析的基础上,基于风圈半径、移速、强度和离岸距离等变量,提出一种针对海上风电场的热带气旋灾害预警时间估算方法,并根据不同风圈半径给出其预警时间的空间分布特征,为有效利用海上风能和开展抗台风措施提供参考。

Super Typhoon Hinnamnor(2022)with a Record-Breaking Lifespan over the Western North Pacific

Super Typhoon Hinnamnor(2022)was a rare and unique western North Pacific typhoon,and throughout its lifespan,it exhibited all of the major features that pose current challenges in typhoon research.Specifically,during different stages of its lifespan,it experienced a sudden change of track,underwent rapid intensification,interacted and merged with another vortex,expanded in size,underwent rapid weakening,produced a strong cold wake,exhibited eyewall replacement,and underwent extratropical transition.Therefore,a timely identification and review of these features of Hinnamnor(2022),as reported in this article,will help update and enrich the case sets for each of these scientific issues and provide a background for more in-depth mechanistic studies of typhoon track,intensity,and structural changes in the future.We also believe that Hinnamnor(2022)can serve as an excellent benchmark to quickly evaluate the overall performance of different numerical models in predicting typhoon’s track,intensity,and structural changes.

不同类型台风气象场对深圳近海海域风暴潮模拟的比较研究——以台风“山竹”为例

台风引起的风暴增水严重影响沿海地区的生产生活,是造成经济损失最严重的海洋灾害之一。深圳市位于中国南海北部沿岸,是易受风暴潮灾害影响的区域,对深圳近海海域风暴潮开展研究不仅能够提升对风暴潮物理机制的认识,同时对沿海城市有效防灾减灾预警有重要意义。在风暴潮模拟研究过程中,台风气象场是风暴潮模拟准确与否的关键因素。本文针对深圳近海区域海洋环境,以海流模型FVCOM(finite volume community ocean model)和海浪模型SWAN(simulation wave nearshore)为基础,建立了区域风暴潮–波浪耦合模型,分别用再分析气象数据(European center for medium weather forecasting,ECMWF)、理想台风模型(Holland)及大气模型台风模拟结果(weather research and forecast,WRF)作为驱动场条件,对台风“山竹”期间的风暴潮过程进行模拟。结果表明:分辨率较低的ECMWF再分析气象数据难以准确体现台风水平结构,从而导致模拟误差;Holland气象场在整体上能够对台风“山竹”进行准确模拟,但无法再现台风在近岸区域的结构形变,从而导致在蛇口及附近(深圳湾,珠江口内侧)区域的风暴潮模拟水位偏高;WRF对风速、气压、水位、波浪都有较好的模拟效果,且WRF很好的改善了Holland在靠近台风登陆点的区域风暴潮水位偏高的问题,对珠江口、深圳湾区域定量改进约20%~30%。在未来的风暴潮预报中,如果采用类似于Holland这样的理想台风场,需注意上述区域的模拟结果。此外,Holland理想台风场和WRF模型结果驱动下的波浪场模拟效果都较好。

黑潮影响热带气旋强度的统计分析

本文利用东京台风中心(Tokyo-Typhoon Center)发布的热带气旋(Tropical cyclone,TC)best-tracks资料,统计了1979—2019年经过黑潮关键区热带气旋的强度变化特征,并进一步分析了其中的物理机制。统计结果显示,黑潮对不同强度TC的加热效果不同,整体而言,TC外缘靠近黑潮关键区至TC中心进入关键区阶段,TC风速显著增强;TC中心进入关键区后,风速数值的分布范围较集中,黑潮暖水对TC风速的影响与TC当前强度有关,强度较弱的TC风速增强,而强度较强TC的风速下限略增大但其风速均值减小。黑潮暖水通过增加海表面的热通量,造成低层水汽辐合,对流层中层湿度增大,水汽上升至高空释放凝结潜热增多,导致TC暖心增强,垂直速度增大,对流增强,从而增强TC强度。TC暖心变化较低层水汽通量的变化滞后约12 h,导致TC中心移出关键区后强度不会迅速减弱。

基于贝叶斯网络和GIS的热带气旋灾害风险评估

针对热带气旋灾害的复杂性和不确定性,文章基于贝叶斯网络和地理信息系统(geographic information system,GIS)提出了一种新的热带气旋灾害风险评估模型。该模型能够从客观历史数据中自动挖掘灾害影响因素间的因果关系,并以概率形式进行表达和推理,从而对不确定灾害风险进行评估预测。基于1980—2016年中国东南沿海三省(广东、福建、浙江)的热带气旋灾害历史数据进行风险评估实验,选取致灾因子危险性、孕灾环境敏感性、承灾体脆弱性3个方面共计12个评估指标作为模型输入,直接经济损失量化为灾害风险等级作为模型输出,构建基于贝叶斯网络的风险评估模型。然后利用2017—2021年热带气旋灾害数据进行模型检验,评估预测的准确率为80.75%。模型预测的极低、低、中、高和极高风险的相对误差分别为27.72%、8.45%、18.58%、16.52%和19.12%,风险预测值的区划结果在空间形态上与实际灾害损失分布高度一致。此外,还将评估模型构建方法应用于“莫兰蒂”台风灾害个例的风险评估。结果表明,模型评估出的灾害高风险和极高风险区域与实际灾情报告基本一致。由此可见,本研究建立的热带气旋灾害风险评估模型具有较高的准确率和可信度,为热带气旋灾害风险评估提供了一种新的方法途径和技术支撑。

Nourishment and disaster mitigation efficiency of feeding sand on the dry section of a dissipative beach

To explore the nourishment effect and disaster reduction efficiency of a fully dissipative dry beach under the impact of storms,this paper uses the measured topography and hydrodynamic data to establish a one-dimensional numerical model of the XBeach beach profile.By numerically modeling the change in the nourished profile for different dry beach widths under normal waves and storm conditions and the recovery process of the profile after the storm,the degree of response in dry beach nourishment for the fully dissipative beach is analyzed.The results show that under normal wave conditions,the response of the nourished dry beach is obvious.Sediment on the dry beach erodes heavily,and the shoreline moves landward over a long distance.With the increase in the width and size of the dry beach,the wave height at the bottom of the backshore profile decreases,the wave height attenuation rate increases continuously,and the wave elimination effect is remarkable.When the storm incident wave intensifies,the wave height attenuation rate of the nourished dry beach decreases,indicating that the smaller the storm intensity is,the more significant the wave reduction effect of the nourished dry beach is.At the same time,different profile arrangements of nourished dry beaches suffer from different degrees of erosion under storm conditions,with significant changes in profile morphology.With intensified storm action,the intensity of sediment erosion in the nourished dry beach increases,the nourishment is weakened,and the recovery effect of the profile after the storm is not obvious.The results of the numerical modeling highlight that the dry beach nourishment method can resist storms to a certain extent,but the overall effect is relatively limited.

Hazard risk assessment of tropical cyclones based on joint probability theory

The main hazard-causing factors of tropical cyclones are strong wind,heavy rainfall,and storm surge.Evaluation of the hazard-causing degree of a tropical cyclone requires a joint intensity analysis of these hazard-causing factors.According to the maximum hourly mean wind speed,total rainfall,and maximum tide level at various observation stations in Hong Kong during these tropical cyclones,three hazard-causing indices for tropical cyclones are introduced:the strong-wind index(VI),total-rainfall index(RI),and tide-level index(LI).Through a joint probability analysis of VI,RI,and LI for a tropical cyclone affecting Hong Kong,the joint return period is calculated to evaluate its joint hazard-causing intensity.A limit state function of Hong Kong’s resistance to tropical cyclones is developed and used to evaluate the regional risk of tropical cyclones affecting Hong Kong.The results indicate that the joint return period of VI,RI,and LI can reflect the joint hazard-causing intensity of strong wind,heavy rain,and storm surge caused by tropical cyclones;if the overall design return periods of the regional structures decrease,the regional ability to defend against tropical cyclone disasters is degraded.