Statistical analysis of tropical disturbances over the South China Sea during 1997�C2006

Tropical disturbances over the South China Sea (SCS) during the period of 1997-2006 are analyzed using the Tropical Storm and Hurricane WX products. A total of 158 tropical disturbances were formed over the SCS from 1997 to 2006, with 54 de-veloping tropical disturbances which developed into tropical depressions and 104 non-developing tropical disturbances which never developed into tropical depressions. The development rate of tropical disturbances into tropical depressions was 34.18% in these ten years. During the period of this study, total annual numbers of tropical disturbances and developing tropical disturbances over the SCS had significant decreasing trends; however, the development rate of tropical disturbances had an insignificant increasing trend.     

基于路径相似的登陆热带气旋降水之动力-统计集合预报模型

数值天气预报(NWP)过去几十年在热带气旋(TC)预报方面的最大进步是越来越准确的路径预报。对于登陆TC降水的预报,目前以数值模式为代表的技术手段预报能力还十分有限。围绕动力-统计结合之方法研究,初步发展了登陆热带气旋降水(LTP)预报的一种新方法:基于路径相似的登陆热带气旋降水之动力统计集合预报(LTP_DSEF)模型。该方法主要分为五步:TC路径预报、相似路径TC识别、其他特征相似性的判别、TC降水集合预报和最佳预报方案选择;涉及两个关键技术:TC降水分离的客观天气图分析法(OSAT)和TC路径相似面积指数(TSAI)。LTP DSEF模型对2012-2016年影响华南地区出现最大日降水量≥100 mm的21个TC的定量降水预报(QPF)试验结果显示,该模型对登陆TC过程降水的预报结果优于动力模式。登陆TC过程降水≥50 mm情况下,建模样本和独立样本平均TS评分均高于动力模式(EC、GFS、T639)相应的最好表现。对LTP_DSEF模型三个最佳方案的参数取值分析显示,起报时刻参数设定为最临近影响时刻即TC对陆地产生降水的前一天12:00 UTC、集合参数取最大值时预报效果稳定趋好。     

Suspended sediment transport during tropical‐cyclone floods in Fiji

Flow records, rising‐stage sediment samplers, and a sand suspension model are used to examine suspended sediment concentrations during major floods caused by tropical cyclones TC Joni and TC Kina in the Rewa River, Fiji. The highest concentrations of total suspended solids were measured during the early stages of TC Kina. The suspension model predicts higher sand concentrations for TC Kina compared with TC Joni because of the larger slope and higher shear stresses during Kina. Extremely high wash load concentrations early in TC Kina are at least partly due to remobilization of fine sediment deposited during the earlier TC Joni flood. Samples from the TC Kina had volumetric concentrations larger than 5%, indicating hyperconcentrated streamflows. Mass‐density shear stresses in the hyperconcentrated flows are up 1·6 times larger than clear‐water shear stresses, but they occur early during low stages of the flood and probably do not result in severe bed erosion. Copyright © 2002 John Wiley & Sons, Ltd.     

An Elliptical Wind Field Model of Typhoons

1　Introduction　Thestormsurgeisoneofthemostimportantphe nomenathatendangerthecoastalengineeringfacili ties .Everyyearthereareabout 1 2tropicalcyclonesmakinglandfallatthemainlandofChinafromMaytoOctober (MuandTu ,2 0 0 0 ) .Whentheastronomictideishigh ,the…     

2020年冬季海洋天气评述

2020年冬季（2020年12月－2021年2月）大气环流特征为：北半球极涡呈偶极型分布,中高纬环流呈 3 波型分布,西风带槽脊较常年明显偏强。位势高度距平场显示,东亚中纬度地区处于负距平区,东亚大槽较常年同期显著偏强,冷空气活动频繁、强度偏强。我国近海出现了 11 次 8 级以上大风过程,其中冷空气大风过程 7 次,冷空气和入海气旋共同影响的大风过程 2 次,冷空气和台风共同影响的大风天气过程以及温带气旋大风过程各 1 次。我国近海出现大范围的海雾过程 4 次,海雾区域主要出现在渤海、渤海海峡、黄海北部和中部海域、琼州海峡、雷州半岛沿岸海域及北部湾,出雾时段多集中于夜间至早晨。西北太平洋和南海共生成 2 个热带气旋;全球其他海域共生成热带气旋 16 个。我国近海出现 2 m以上大浪过程的天数有 54 d,约占冬季总日数的 60%。冬季,我国近海海域呈明显降温过程,北部海域的降温幅度明显大于南部海域,海面温度从北到南的温差在冬季由 2020 年 12 月的 23 ℃加大到 2021 年 2 月的 27 ℃。     

Study of the Wind Conditions in the South China Sea and Its Adjacent Sea Area

An increasing number of marine structures have been built for coastal protection and marine development in recent years,and wind,which is crucial to marine structures,should be analyzed.Therefore,typhoon frequency,wind climate,wind energy assess-ment,and extreme wind speed in the South China Sea(SCS)are investigated in detail in this study.The data are obtained from the China Meteorological Administration,the European Centre for Medium-range Weather Forecasts,and the National Centers for Envi-ronmental Prediction.The offshore wind energy potential is analyzed at five sites near the coast.The spatial and monthly frequencies of tropical cyclones for different intensity categories are analyzed.The extreme wind speed is fitted by five distribution models,and the generalized extreme value(GEV)distribution is selected as the most suitable function according to the goodness of fit.The spa-tial distributions of extreme wind speeds in the SCS are plotted on the basis of the GEV distribution and ERA5 data sets.The influ-ences of the distribution models and data sets on the calculated results are discussed.Moreover,the monthly extreme wind speed and comparison with the results of previous studies are analyzed.This study provides a reference for the design of wind turbines.     

中国沿海登陆热带气旋活动特征分析

热带气旋是危害中国最严重的天气系统,分析和认识中国沿海登陆热带气旋活动的新特征对防灾减灾具有重要意义。依据近70年气象资料,采用统计学方法,对登陆中国沿海的热带气旋特征进行分析,研究发现:在气候变化的背景下,登陆中国的热带气旋发生了明显变化。近年台风登陆频数高于往年平均,其整体强度和最大值均呈增大趋势,年台风强度的不稳定性加剧;研究还发现台风强度越高,其生成地纬度带范围越窄且越靠近赤道;建立了高强度热带气旋（STY和SUPER TY）时间和纬度的关系"φ—m"。检验了台风季长与初旋日呈负相关且不受厄尔尼诺现象影响,台风季长符合正态分布并给出概率密度公式。     

数值预报产品统计释用技术在热带气旋路径客观预报中的应用

首先对应用数值预报产品统计释用技术的效果进行了统计,结果表明,数值预报产品统计释用技术的应用改善了热带气旋路径客观预报中预报因子的预报能力,提高了模式的预报技巧并拓展了有效预报时效。继而对热带气旋路径客观预报中若干统计释用技术问题进行了讨论,并指出：在应用数值预报产品构造热带气旋路径客观预报模式时,采用大样本资料和完全预报方法,细心构造反映各种天气系统特征和物理量场的预报因子,应用多时刻ＮＷＰ产品并对ＮＷＰ产品进行统计订正。对多种预报模式的预报结果进行综合集成等技术是提高预报技巧和稳定性的有效途径。     

东海转向和登陆热带气旋特征合成分析

进入东海的热带气旋（TC）每年有3.2个,转向或者登陆将造成不同的影响。通过对这两类TC登陆或转向前后,形势场和物理量场的合成分析得到：转向类TC,副热带高压(以下简称副高)弱,东侧呈块状;西风带强,离TC近;中高层西风急流明显,急流在向东移动过程中有增强趋势;TC东北方高层辐散增强,在中低层有正涡度平流,涡度平流中心清晰。而登陆类TC,副高强,呈宽带状;西风带弱,离TC远;西风急流不明显,没有增强,高层急流中心位于TC的西北方和北方;TC东北方高层没有明显的辐散流出,中低层正涡度平流位于TC的西北方和北侧,涡度平流中心不清晰。转向或登陆前72 h各特点已有显示,前48 h其特征更加明显。     

TROPICAL CYCLONE GENESIS EFFICIENCY：MID-LEVEL VERSUS BOTTOM VORTEX

Cloud resolving Weather Research and Forecasting(WRF)model simulations are used to investigate tropical cyclone(TC)genesis efficiency in an environment with a near bottom vortex(EBV)and an environment with a mid-level vortex(EMV).Sensitivity experiments show that the genesis timing depends greatly on initial vorticity vertical profiles.The larger the initial column integrated absolute vorticity,the greater the genesis efficiency is.Given the same column integrated absolute vorticity,a bottom vortex has higher genesis efficiency than a mid-level vortex.A common feature among these experiments is the formation of a mid-level vorticity maximum prior to TC genesis irrespective where the initial vorticity maximum locates.Both the EMV and EBV scenarios share the following development characteristics:1)a transition from non-organized cumulus-scale(~5 km)convective cells into an organized meso-vortex-scale(~50 to 100 km)system through upscale cascade processes,2)the establishment of a nearly saturated air column prior to a rapid drop of the central minimum pressure,and 3)a multiple convective-stratiform phase transition.A genesis efficiency index(GEI)is formulated that includes the following factors:initial column integrated absolute vorticity,vorticity at top of the boundary layer and vertically integrated relative humidity.The calculated GEI reflects well the simulated genesis efficiency and thus may be used to estimate how fast a tropical disturbance develops into a TC.