Kinetic Energy Budgets during the Rapid Intensification of Typhoon Rammasun (2014)

In this study,Typhoon Rammasun(2014)was simulated using the Weather Research and Forecasting model to examine the kinetic energy during rapid intensification(RI).Budget analyses revealed that in the inner area of the typhoon,the conversion from symmetric divergent kinetic energy associated with the collocation of strong cyclonic circulation and inward flow led to an increase in the symmetric rotational kinetic energy in the lower troposphere.The increase in the symmetric rotational kinetic energy in the mid and upper troposphere resulted from the upward transport of symmetric rotational kinetic energy from the lower troposphere.In the outer area,both typhoon and Earth’s rotation played equally important roles in the conversion from symmetric divergent kinetic energy to symmetric rotational kinetic energy in the lower troposphere.The decrease in the symmetric rotational kinetic energy in the upper troposphere was caused by the conversion to asymmetric rotational kinetic energy through the collocation of symmetric tangential rotational winds and the radial advection of asymmetric tangential rotational winds by radial environmental winds.

The Structure and Rainfall Features of Tropical Cyclone Rammasun (2002)

Tropical Rainfall Measuring Mission (TRMM) data [TRMM Microwave Imager/Precipitation Radar/Visible and Infrared Scanner (TMI/PR/VIRS)] and a numerical model are used to investigate the structure and rainfall features of Tropical Cyclone (TC) Rammasun (2002). Based on the analysis of TRMM data, which are diagnosed together with NCEP/AVN [Aviation (global model)] analysis data, some typical features of TC structure and rainfall are preliminary discovered. Since the limitations of TRMM data are considered for their time resolution and coverage, the world observed by TRMM at sev- eral moments cannot be taken as the representation of the whole period of the TC lifecycle, therefore the picture should be reproduced by a numerical model of high quality. To better understand the structure and rainfall features of TC Rammasun, a numerical simulation is carried out with mesoscale model MM5 in which the validations have been made with the data of TRMM and NCEP/AVN analysis.

THE EFFECT OF SAMPLE OPTIMIZATION ON THE ENSEMBLE KALMAN FILTER IN FORECASTING TYPHOON RAMMASUN(2014)

In a limited number of ensembles, some samples do not adequately reflect the true atmospheric state and can in turn affect forecast performance. This study explored the feasibility of sample optimization using the ensemble Kalman filter(EnKF) for a simulation of the 2014 Super Typhoon Rammasun, which made landfall in southern China in July 2014. Under the premise of sufficient ensemble spread, keeping samples with a good fit to observations and eliminating those with poor fit can affect the performance of En KF. In the sample optimization, states were selected based on the sample spatial correlation between the ensemble state and observations. The method discarded ensemble states that were less representative and, to maintain the overall ensemble size, generated new ensemble states by reproducing them from ensemble states with a good fit by adding random noise. Sample selection was performed based on radar echo data. Results showed that applying En KF with optimized samples improved the estimated track, intensity,precipitation distribution, and inner-core structure of Typhoon Rammasun. Therefore, the authors proposed that distinguishing between samples with good and poor fits is vital for ensemble prediction, suggesting that sample optimization is necessary to the effective use of En KF.

INFLUENCE OF MODEL HORIZONTAL RESOLUTION ON THE INTENSITY AND STRUCTURE OF RAMMASUN

We use the WRF(V3.4) model as the experimental model and select three horizontal resolutions of 15, 9,and 3 km to research the influence of the model's horizontal resolution on the intensity and structure of the super-strong typhoon Rammasun(1409) in 2014. The results indicate that the horizontal resolution has a very large impact on the intensity and structure of Rammasun. The Rammasun intensity increases as the horizontal resolution increases. When the horizontal resolution increases from 9 km to 3 km, the enhancement of intensity is more obvious, but the strongest intensity simulated by 3 km horizontal resolution is still weaker than the observed strongest intensity. Along with the increase of horizontal resolution, the horizontal scale of the Rammasun vortex decreases, and the vortex gradually contracts toward its center. The vortex structure changes from loose to compact and deep. The maximum wind radius,thickness of the eye wall, and outward inclination of the eye wall with height decrease, and the wind in the inner core region, updraft motion along the eye wall, and strength of the warm core become stronger. Additionally, the pressure gradient and temperature gradient of the eye wall region increase, and the vortex intensity becomes stronger. When the horizontal resolution increases from 9 km to 3 km, the change in the Rammasun structure is much larger than the change when the horizontal resolution increases from 15 km to 9 km. When the model does not employ the method of convection parameterization, the Rammasun intensity simulated with 3 km horizontal resolution is slightly weaker than the intensity simulated with 3 km horizontal resolution when the Kain-Fritsch(KF) convection parameterization scheme is adopted, while the intensity simulated with 9 km horizontal resolution is much weaker than the intensity simulated with 9 km horizontal resolution when the KF scheme is adopted. The influence of the horizontal resolution on the intensity and structure of Rammasun is larger than the influence when the KF scheme is adopted.

THE EFFECT OF MODEL HORIZONTAL RESOLUTION ON THE PRECIPITATION OF RAMMASUN

This paper investigates the effect of horizontal resolution on the precipitation of the super typhoon Rammasun(1409). The experiment uses WRF(V3.4) model with resolutions of 15 km, 9 km and 3 km. The results suggest that the simulated Rammasun rain band shapes and distributions at different horizontal resolutions are nearly the same. When the resolution is increased from 15 km to 9 km and then to 3 km, heavy precipitation is observed to spread in all directions from a concentrated distribution, especially when the resolution is increased from 9 km to 3 km. The 6 h and 1 h heavy precipitations also show a more significant comma-shape distribution. Moreover, the water vapor distribution shows the same characteristics as the heavy precipitation with a notably enhanced ascending movement and a decreased height of the strongest ascending movement. Of the three resolutions, the precipitation distribution simulated at 3 km resolution is the closest to the observed distribution; however, there is still a noticeable difference between the simulated precipitation and the actual observation. With the absence of the convection parameterization in the model, the precipitation distributions simulated at 9 km and 3 km resolutions demonstrate the same features as when the KF convection parameterization is applied. However, the simulated precipitations at these two resolutions are smaller than those obtained with the KF scheme. Meanwhile the difference between the simulated precipitations at these two resolutions is also smaller than that in the latter case. In general, when KF scheme is applied to the model, the simulation effect of Rammasun precipitation is better than that obtained without the convection parameterization scheme.

Role of ocean upper layer warm water in the rapid intensification of tropical cyclones: A case study of typhoon Rammasun(1409)

Rammasun intensified rapidly from tropical storm to super typhoon in the northern South China Sea（NSCS）before its landfall on Hainan Island. Analysis of observed data shows that the anomalous ocean upper layer warm water（WW） is important to the rapid intensification of Rammasun. During the period of Rammasun, sea surface temperature（SST） in the NSCS was much warmer than the climatological SST. The anomalous WW supplied more energy to Rammasun, resulting in its rapid intensification. Numerical simulations further confirm that the NSCS WW plays an important role in the rapid intensification of Rammasun. As the WW is removed, the intensification of Rammasun is only 25 h Pa, which is 58.1% of that in the original SST-forced run.

A High-resolution Simulation of Supertyphoon Rammasun(2014)--Part Ⅰ:Model Verification and Surface Energetics Analysis

A 72-h high-resolution simulation of Supertyphoon Rammasun （2014） is performed using the Advanced Research Weather Research and Forecasting model. The model covers an initial 18-h spin-up, the 36-h rapid intensification （RI） period in the northern South China Sea, and the 18-h period of weakening after landfall. The results show that the model reproduces the track, intensity, structure of the storm, and environmental circulations reasonably well. Analysis of the surface energetics under the storm indicates that the storm＇s intensification is closely related to the net energy gain rate （eg）, defined as the difference between the energy production （PD） due to surface entropy flux and the energy dissipation （Ds） due to surface friction near the radius of maximum wind （RMW）. Before and during the RI stage, the ~：g is high, indicating sufficient energy supply for the storm to intensify. However, the Sg decreases rapidly as the storm quickly intensifies, because the Ds increases more rapidly than the PD near the RMW. By the time the storm reaches its peak intensity, the Ds is about 20% larger than the PD near the RMW, leading to a local energetics deficit under the eyewall. During the mature stage, the PD and Ds can reach a balance within a radius of 86 km from the storm center （about 2.3 times the RMW）. This implies that the local PD under the eyewall is not large enough to balance the Ds, and the radially inward energy transport from outside the eyewall must play an important role in maintaining the storm＇s intensity, as well as its intensification.

Strengthening effect of super typhoon Rammasun(2014)on upwelling and cold eddies in the South China Sea

Typhoon is one of the frequent natural disasters in coastal regions of China.As shown in many studies,the impact of typhoons on the South China Sea(SCS)should not be overlooked.Super typhoon Rammasun(2014)was studied that formed in the northwestern Pacific,passed through the SCS,then landed in the Leizhou Peninsula.Remote sensing data and model products were used to analyze the spatiotemporal variations of the cold eddies,upwelling,sea surface temperature,mixed layer depth,rainfall,sea surface salinity,suspended sediment concentration,and surface-level anomaly.Results confirm the constant presence of upwelling and cold eddies in the southeast of Hainan(north of the Zhongsha Islands)and the southeast of Vietnam in July.In addition,we found the strengthening effect of super typhoon Rammasun on the upwelling and cold eddies in the SCS.The major reasons for the continuous decrease in sea surface temperature and the slow regaining of seawater temperature were the enhanced upwelling and vertical mixing caused by the typhoon.The increasing of the surface runoff in the Indochina Peninsula was mainly affected by the typhoon,with some contribution for the southeast of Vietnam’s cold eddy and upwelling.

Analysis of Special Strong Wind and Severe Rainstorm Caused by Typhoon Rammasun in Guangxi, China

Based on conventional meteorological observation data, NCEP 1° × 1° reanalysis data, reanalysis data with resolution 0.75° × 0.75° from ECMWF and Doppler weather radar, we analyzed the weather conditions and physical characteristics of Super Typhoon Rammasun (1409), which caused special strong wind and severe rainstorm in Guangxi. The results show that: 1) Typhoon Rammasun offshore sudden strengthening in one of the main reasons was that loop pressure ridge superimposed into the westward extension of subtropical high, to making enable rapid strengthening of the subtropical high, so the subtropical high advanced faster than the Rammasun move, Rammasun center of the subtropical high distance reduced and the gradient increased;2) Rammasun northward to south china coast with plenty of vapor following ITCZ, before landing, southwest monsoon and cross-equatorial flow were involved, Rammasun got latent heat of monsoon jet, enabling it to strengthen in offshore;3) Rammasun from the Qiongzhou Strait into the northern Gulf, therefore the Strait of short passages and both sides belong to the low zone, friction consumption smaller, that was the main reason what was able to maintain the strength of the super typhoon, when Rammasun into the Beibu Gulf;4) Diagnostic analysis shows that Rammasun before entering the northern Gulf and into the Beibu Gulf later, vorticity weakened, divergence and vapor flux divergence changed were smaller, meanwhile, vertical ascent speed and latent heat transport both increased, which was important reason of severe rainstorm caused by Rammasun.

Restoration of Wind Speed in Qinzhou, Guangxi during Typhoon Rammasun

In 2014,Typhoon Rammasun invaded Qinzhou,Guangxi,causing damage to the wind tower sensor at 80 m in Qinzhou.In order to restore the wind speed at 80 m at that time,this paper was based on the hourly average wind speed data of the wind tower and meteorological station from 2017–2019,and constructed the wind speed related model of Meteorological Station and the wind measuring tower in Qinzhou,Moreover,this paper Based on the hourly average wind speed data of Qinzhou Meteorological Station in 2014,Restored the hourly average wind speed of the anemometer tower during Rammasun landfalled.The results showed it is significant correlation that the hourly mean wind speed of the wind tower at 80 m and the hourly mean wind speed of meteorological station at 100 m(R2=0.9632),and speed of the wind measuring tower and speed of meteorological station constitutes an equation,This equation is Y=0.7834X.The hourly average wind speed of the wind tower at 80 m during the 2014 Rammasun Landing was restored using this model.See the results in Schedule 4.

基于Holland台风模型及三重嵌套海浪模式的台风浪数值模拟研究

现有的风场资料存在台风中心附近风速偏低的问题。为改进台风期间风场数据,使用Holland经验台风模型结合多平台交叉校准数据(cross-calibrated multi-platform,CCMP)及欧洲中期天气预报中心的再分析数据(European Centre for Medium-range Weather Forecasts Reanalysis data,ERA5)风场资料,研究了不同台风最大风速半径(maximum wind radius of the typhoon,RMW)、Holland B参数对模拟效果的影响,确定了最优模拟参数,并以改进后的风场驱动三重嵌套海浪模型对台风“威马逊”发生期间的台风浪进行模拟。模拟结果与实测数据对比表明,(1)改进的风场资料与实测结果更为接近,作为海浪模式驱动项可更好地模拟台风期间波浪状况;(2)三重嵌套海浪模型的波浪模拟效果优于单独的海浪模型。

FORECAST AND SERVICE PERFORMANCE ON RAPIDLY INTENSIFICATION PROCESS OF TYPHOONS RAMMASUN(2014) AND HATO(2017)

Super typhoons Rammasun(No.1409) and Hato(No.1713) both underwent rapidly intensification(RI) in the northern part of South China Sea before they made landfall. Forecast skills and service performance of tropical cyclones' RI process in the real-time operation is analyzed in this study. TCs are prone to intensify rapidly in the South China Sea, which is a complex process concluding complicated interaction between large scale environmental systems and tropical cyclone inner-core structure. The forecast performance of Rammasun and Hato shown that the subjective forecast of CMA has defect in the intensity forecast especially for the long-rang more than 48-hr. However, forecasters have chance to capture the signal of RI besides numerical operational models, which contribute to gain precious time for disaster reduction affairs. The role of local sea surface temperature and the warm core structure revealed by the numerical simulations are highlighted in doing comprehensive analysis in real-time forecast.

台风“威马逊”(1409)和“海鸥”(1415)影响广西风雨特征及预报偏差的比较分析

基于观测资料、数值模式产品及主观预报,对2014年超强台风“威马逊”和强台风“海鸥”影响广西的风雨特征及预报偏差进行对比分析。结果表明:(1)“威马逊”深入广西内陆,高层辐散更强,副高西脊点偏东,低层急流南北宽度更广且风速更大,台风强度更强,这是“威马逊”强降雨范围更广,小时雨强更强的可能原因。(2)主客观预报台风路径及强度随预报时效增加误差明显增大且差别较明显。ECMWF、广西遗传神经网络与中央台分别对台风路径、台风强度预报有很好的参考价值。(3)主客观均能报出强降水的形态但强度偏弱,预报误差随时效增加而增大且存在明显的空漏报。大暴雨量级预报评分ECMWF_HR明显高于广西主观,暴雨量级预报评分总体是广西主观优于ECMWF_HR。(4)ECMWF_HR没有准确预报副高西进南扩过程;副高预报的偏东偏北,是导致台风和急流中心偏南偏弱的可能原因。(5)ECMWF_HR预报850hPa水汽通量及其散度与实况在形态上基本一致,但位置偏西偏南,强度偏弱,这与预报副高偏东及台风偏西偏弱相关,应该引起今后业务预报关注。

超强台风“威马逊”对南海西北海域海洋环境的影响

2014年第9号超强台风"威马逊"(1409)过境南海并穿越琼州海峡进入北部湾,给海南、广东和广西造成了严重损失,并对南海西北海域海洋动力与生态环境产生了重要的影响。文章利用卫星遥感水色水温及风场数据,分析了台风前后海表温度、悬浮泥沙浓度、叶绿素浓度、初级生产力及上升流分布特征与变化。研究结果表明:超强台风"威马逊"诱发了强烈的混合夹卷和上升流,并加强了季节性上升流;海表温度最大降幅近2℃,相对台风路径呈显著的"右偏性",而台风引起的强降水却具强烈的"左偏性";台风后悬浮泥沙浓度平均升高51.4%,叶绿素浓度增幅达28%,且最大浓度有3d的延迟,初级生产力增加34%;上层水体混合加剧,混合层深度平均增长近10.4m。

2014年超强台风“威马逊”灾害特征与社会致灾机制分析

台风是一种具有严重破坏性的天气事件,认识超强台风造成的洪涝灾害特点、成灾机制,以及社会响应特征对于水利防灾减灾具有重要意义。通过对2014年超强台风"威马逊"给海南省带来的严重洪涝灾害进行系统调查分析,发现此次灾害呈现出的特点是:受灾人口比重大,人员伤亡严重;农业受灾比重较大,成灾比重高;倒塌房屋数量巨大;灾害损失严重,农林牧渔业损失严重,水利损失较轻。进一步的分析表明:建筑设计标准偏低,基础设施管理有待完善;基层防台专业组织管理乏力,社区居民避险自救能力弱,社会综合减灾能力不足等社会防灾减灾体系不健全;法规预案体系不健全等是造成此次灾害严重损失的主要因素。据此,从结构性减灾(基础设施)和非结构性减灾(制度建设、社会参与)两方面提出今后防御超强台风的建议。

强潮海滩响应威马逊台风作用动力沉积过程研究——以北海银滩为例

研究台风影响下的海滩沉积过程不仅可加深极端海况下的海滩冲淤变化理解,而且有利于海滩资源的保护与海岸工程保护。以强潮海滩——北海银滩为例,通过采集北部湾海区1409号威马逊超强台风作用前后的沉积物、剖面高程及水文资料,探讨强潮海滩的动力沉积过程。结果表明:1)台风作用前后的海滩沙丘-滩肩-沙坝体系的地貌状态基本不变,其中沉积物组分均为砂,细砂、极细砂和中砂三组分平均含量占所有组分的95%以上;与台风作用前比较,台风后的地貌在维持先前形态的条件下,发生局部侵蚀和后退,沉积物相对变粗且细砂含量增加了10%。2)台风作用后后滨沙丘侵蚀,且沉积物滚动组分增加;冲流带和滩肩前缘沉积物的搬运由双跳跃转为单一的跳跃形式。3)台风作用前后的海滩沉积物主要变化过程可由两个模态表征,其中主要模式反映了台风作用前后的海滩以细砂为主的动力沉积变化特征,该模式受控于区域波浪和潮汐的长期耦合作用,并以波浪为主导因素。台风作用前的次要模式反映潮汐作用控制下的海滩沉积横向振荡特征;台风作用后的次要模式表征了台风影响下的海滩横向沉积物偏粗、冲流带-低潮带振荡及其沉积分异过程。

海滩-珊瑚礁系统风暴响应特征研究——以1409号台风“威马逊”对清澜港海岸影响为例

珊瑚礁海岸在我国热带地区广泛发育,海滩-珊瑚礁海岸的动力地貌过程是认识该类海岸的关键。本文基于对海南铜鼓岭-高隆湾岸段的台风＂威马逊＂前后跟踪观测,讨论了海滩风暴响应特征及其与珊瑚礁发育之间的联系。结果表明该岸段海滩在＂威马逊＂风暴作用下响应最为剧烈的区带位于平均海平面（MSL）以上,表现为后滨冲越,以及岸线蚀退、滩肩变窄、滩面侵蚀等响应特征。海滩风暴响应特征与近岸珊瑚礁发育密切相关,在无珊瑚或珊瑚受损的岸段海滩响应剧烈,剖面平均变化率（MPC）为其他岸段的3~6倍,珊瑚礁通过消耗波能对相邻海滩提供良好保护。海滩-珊瑚礁系统对风暴的响应特征受控于珊瑚礁对海岸波浪的消耗能力和海滩固有的缓冲能力。基于本文研究结果,归纳出风暴极端动力条件下海滩-珊瑚礁海岸的4种风暴响应模式。

超强台风“威马逊”(1409)强度和降水特征及其近海急剧加强原因

利用常规观测资料以及海南省中尺度自动站资料、海口多普勒雷达产品、FY系列卫星云图和NECP 1°×1°再分析资料,分析了2014年第9号超强台风"威马逊"(1409)在海南岛登陆前后其强度和降水特征及其近海急剧加强的原因。结果表明:"威马逊"登陆海南省文昌市翁田镇时强度维持或略有减弱,登陆前其中心附近极大风速超过74 m·s-1,最低海平面气压899.2 h Pa,为1949年建国以来登陆我国大陆最强台风;"威马逊"从7月18日10时到当日15时登陆文昌前的5 h内,其中心附近最大风速增大了5 m·s-1,最低气压下降了20 h Pa,其超强台风量级从18日11时开始维持时间达17 h;"威马逊"眼壁回波造成的海南北部地区强降水具有降水效率高、对流发展不够强盛的混合性降水特征,而其螺旋雨带"列车效应"造成的海南西部地区极值降水则具有典型的对流性降水特征;西太平洋副热带高压、低空急流、西风槽和南亚高压是"威马逊"近海持续加强的主要影响系统;低层辐合与高层辐散、弱的环境风垂直切变和适宜的海面温度、深厚的暖涡是"威马逊"近海急剧加强的原因。

利用TRMM资料对热带气旋“威马逊”结构及其降水特征的研究

利用NASA提供的热带测雨卫星(TRMM)资料和NCEP/AVN模式的实况分析场研究了热带气旋“威马逊”(2002)的演变过程、结构和降水特征.对要素场及倾斜对流有效位能诊断分析发现,降水的分布和强度对热带气旋的发展有很好的指示作用.针对MM5的几种积云参数化方案进行了数值试验,初步研究了各方案在热带气旋定量降水预报(QPF)中的作用.

1409号和1415号台风风暴潮预报的数值研究

分析了1409"威马逊"和1415"海鸥"台风特点及风暴潮、潮位情况。给定较准确的台风特征参数并利用ADCIRC模式对两次台风风暴潮进行数值模拟,各站模拟与实测吻合良好,选取海南岛北部铺前湾作为重点岸段,利用秀英站的风暴潮模拟及北港岛灾后调查推断铺前湾口(P1)、湾顶(P2)输出点的风暴潮模拟值可信度高。对于环流范围较小的超强台风1409"威马逊",P1和P2的模拟最大增水明显高于秀英站,而P2又明显高于P1;对于环流范围较大的台风1415"海鸥",P1、P2的模拟最大增水与秀英站无显著差别。因此,台风特征的预报判断将是风暴潮预报的重要因素。