EFFECTS OF SST, VWS, AND DCC UPON RAPID INTENSIFICATION OF OFF-SHORE TYPHOONS IN CHINA SEAS

In this study, we employed National Centers for Environmental Prediction(NCEP)/National Center for Atmospheric Research(NCAR) reanalysis data and records from the China Meteorological Administration(CMA)Yearbook of Tropical Cyclones to investigate three factors: sea-surface temperature(SST), vertical wind shear(VWS),and the density of the core convection(DCC), which are responsible for the rapid intensification(RI) of 1949-2013 offshore typhoons. Our analysis results of these composite factors show that in the environmental wind field the typhoons are far away from the outer strong VWS; in the SST field they are in the high SST area; and the core convective activity is robust and takes a bimodal pattern. The difference in RI between typhoons over the East China Sea(ECS) and the South China Sea(SCS) is a smaller VWS for the ECS typhoons, which may be one of the reasons why typhoons in the ECS are more intense than those in the SCS. Our study results indicate that SST, VWS, and DCC can result in an RI after a certain time interval of 36 h, 24 h to 30 h, and 24 h, respectively. The RI indicates a lag in the atmospheric response to oceanic conditions. This lag characteristic makes it possible to predict RI events. In summary, where the SST is high(≥28 ℃), the VWS is small, and the DCC is high, an RI will occur. Where mid-range SSTs occur(26 ℃≤SST≤28 ℃), with small VWS, and high DCC, the RI of typhoons is also likely to occur.     

DYNAMIC FACTORS RELATED TO DECAY PROCESS OF OFFSHORE TROPICAL CYCLONES IN NORTHWEST PACIFIC

Intensity variation of tropical cyclones(TCs),especially that of coastal or landfalling TCs,is of great concern in current research.Most of the research papers,however,focus on intensification processes of TCs;only a few discuss decay processes in the lifetime of a TC.In the daily weather operation related to TCs,it is challenging when a TC weakens and/or disappears suddenly,because it brings more difficulties than the forecast of intensifying TCs does.Overestimation of a decaying landfalling TC would lead to over-preparation of defensive measures and result in"crying wolf"mentality with adverse effects.This study summarized physical mechanisms that dominate the decaying process of TCs and listed several possible dynamical factors:reduced level of air temperature,too large or too small speed,contraction of TC size amplification of TC’s core,and lightning number in a TC.     

NUMERICAL SIMULATION STUDY ON THE RAPID INTENSIFICATION OF TYPHOON HAIKUI (1211) OFF THE SHORE OF CHINA

Forecasting the rapid intensification of tropical cyclones over offshore areas remains difficult. In this article, the Weather Research and Forecast (WRF) model was used to study the rapid intensification of Typhoon Haikui (1211) off the shore of China. After successful simulation of the intensity change and track of the typhoon, the model output was further analyzed to determine the mechanism of the rapid change in intensity. The results indicated that a remarkable increase in low-level moisture transportation toward the inner core, favorable large-scale background field with low-level convergence, and high-level divergence played key roles in the rapid intensification of Typhoon Haikui in which high-level divergence could be used as an indicator for the rapid intensity change of Typhoon Haikui approximately 6 h in advance. An analysis of the typhoon structure revealed that Typhoon Haikui was structurally symmetric during the rapid intensification and the range of the eyewall was small in the low level but extended outward in the high level. In addition, the vertically ascending motion, the radial and tangential along wind speeds increased with increasing typhoon intensity, especially during the process of rapid intensification. Furthermore, the intensity of the warm core of the typhoon increased during the intensification process with the warm core extending outward and toward the lower layer. All of the above structural changes contributed to the maintenance and development of typhoon intensity.     

登陆我国台风研究概述

首先对登陆我国台风活动的气候特征分析指出，登陆我国的台风频数存在明显的月际、年际和年代际差异；登陆台风具有明显的周期特征和时间日变化特征；并指出了登陆我国台风与厄尔尼诺的联系。对中心最大风速≥17．2m/s的登陆台风移动趋势进行了统计分析，结果表明不同移动趋势的登陆台风频数不仅与季节有关，还与登陆地段有关。其次总结了近几十年有关登陆台风研究的成果。     

2006号台风“米克拉”近海急剧增强诊断分析

利用ERA-5再分析资料、日本葵花8号卫星黑体亮温资料以及中国气象局上海台风研究所台风最佳路径集资料,对2020年第6号台风“米克拉”（2006）近海强度急剧增强进行诊断分析。（1） 比常年偏暖的29～30 ℃的南海东部海温是“米克拉”急剧增强的有利下垫面条件;200 hPa加强东移的南亚高压、500 hPa加强西伸的副高、低层加强的偏南-西南急流是主要影响系统;相对比深层和高层大气,持续低于4 m/s的低层大气垂直风切是重要因子。（2） “米克拉”的增强主要体现在对流层低层动能的不断增强,在台风急剧增强过程中,中低层的气旋性涡度、低层辐合强度、中高层辐散强度以及上升运动均明显加强;对流层中高层动能在台风急剧增强前的减小可能与增强的高空出流相关。（3） 在“米克拉”急剧增强前,深对流云系强度不断增强,但覆盖面积变化不大;在急剧增强阶段,深对流云系组织的更加紧实集中,覆盖面积明显增大。     

INSTABILITY OF PERTURBATION IN TYPHOONS UNDER THE CONDITIONS OF APPROXIMATE ACTUAL WIND FIELD

With conditions of approximately actual background wind field in typhoons and a barotropic nondivergent model in a cylindrical coordinate, the problem of instability of the perturbation in typhoons isdiscussed. The results show that the warm core structure of typhoons and the activity of fanly strongcold air in the periphery are advantageous to the perturbation development in typhoons,and the strongerthe typhoons, i. e. the lower the pressure, the caster the perturbation in typhoons would develop.     

台风登陆过程中南海近海阵风因子特征

阵风预报对于输电铁塔线路设计、风力发电、建筑和桥梁设计以及航空气象安全等至关重要。目前,基于不同观测资料和计算方法,学者们给出了不同的阵风或阵风因子参数化公式,没有公认的一致结果。利用中国气象局南海(博贺)海洋气象科学试验基地离岸4.5 km和6.5 km的两个海洋气象观测塔在2008—2018年七个台风期间观测的10 Hz高频湍流脉动数据,分析了观测高度、平均时间、下垫面特征和大气稳定度对阵风因子计算结果的影响,研究了近海海上台风过程中阵风因子与平均风速和湍流特征参数的关系。不同于以往研究给出阵风因子是常数,给出了阵风因子随10 m风速变化的计算公式,为阵风预报及相关防灾减灾提供参考依据。     

1949-2007年登陆我国变性热带气旋的特征统计及合成分析

利用1949-2007年热带气旋年鉴等资料,统计分析登陆中国并在我国或附近变性的热带气旋的特征,着重分析不同区域及路径的变性气旋特征.分析结果得出,登陆我国的热带气旋很多,但在我国及附近沿海变性的却较少,大多数热带气旋变性后不发展或迅速衰减,只有约17％的变性热带气旋继续发展.热带气旋变性大多发生在114°E以东,移动...     

ON THE RELATIONSHIP BETWEEN PRECIPITATION ANOMALIES IN THE FIRST RAINING SEASON (APRIL-JUNE) IN SOUTHERN CHINA AND SST OVER OFFSHORE WATERS IN CHINA

Precipitation anomalies in the first raining season of southern China were analyzed, with the suggestion that there are obvious interannual variation of peak values. In the raining season, the general tendency of precipitation is not obvious and the anomalous oscillation is multi-scale. Corresponding to years of more or less precipitation in the raining season, there are sharply opposite distribution across the nation in the simultaneous periods. In addition, by studying the distribution of correlation between anomalous precipitation in southern China in the first raining season and SSTA over offshore waters of China in the preceding period (June ~ August of the previous year), a sensitive zone of waters has been found that has steady effect on the precipitation of southern China in the season. Discussions are also made of the sensitive period, its simultaneous SSTA and subsequent anomalous circulation field in relation to precipitation anomalies and simultaneous circulation field in the first raining season of southern China. In the last part of the work, relationship between the SSTA in the sensitive zone and global SSTA is analyzed. A possible mechanism by which SSTA in offshore Chinese waters affects the precipitation anomalies in the first raining season of southern China is put forward.     

EFFECT OF DRY COLD AIR ACTIVITY ON THE OFFSHORE RAPID INTENSIFICATION OF SUPER TYPHOON SAOMAI (2006): A NUMERICAL SIMULATION RESEARCH

Employing the mesoscale WRF (Weather Research and Forecast) model, Super Typhoon Saomai (2006) is simulated. The variation of track and intensity and its offshore rapid intensification process are well demonstrated by the model, and the temperature and humidity patterns associated with the dry cold air activity and their impact on and mechanism of the offshore rapid intensification of Saomai are mainly studied in this paper. The results indicate that high-resolution water vapor imagery can visually reveal the development, evolution, interaction as well as the mutual complementation of the dry cold air activity accompanied with the development of Saomai. The offshore rapid intensification phenomenon of Saomai is closely related to the dry cold air which originates from the upper- and mid- troposphere. Besides, the dry cold air from the upper troposphere is stronger than that from the mid-troposphere. Saomai intensifies as the dry cold air from the northwest moves toward its circulation but weakens when the dry cold air from the southwest is drawn into the storm. Dry cold airflows and their cold advection effect caused by the downward motion across the isentropic surface are favorable to the development of Saomai. The dry cold air always moves along an isentropic surface from the upper troposphere to the mid-troposphere around the typhoon circulation and contributes to Saomai’s abrupt intensity change.     

华南前汛期降水与我国近海海温的SVD分析

利用国家气象局整编的中国160站月降水资料和英国气象局的全球逐月海温格点资料,分析了华南前汛期降水的异常特征,并用SVD方法分析华南前汛期降水与近海海温的关系。结果表明：近50年华南南部前汛期降水的总的趋势变化不明显。华南南部前汛期降水异常存在3 a、5 a、7 a和14 a的周期;用SVD方法分析发现：存在一个关键区（130~158 ?E,5~18 ?N）,华南前汛期降水异常关键影响时段是前一年5—8月,华南前汛期降水与该关键区海温有较好的负相关关系,即前一年5~8月关键区海温异常偏高（低）,次年华南前汛期降水偏少（多）。     

A STUDY ON THE MECHANISM OF RAPID WEAKENING OF TYPHOON XANGSANE (0020) OVER THE EAST CHINA SEA

Using the National Center for Environmental Prediction reanalysis data on 1.0°×1.0° grids and data from the Tropical Cyclone yearbook(2000),a diagnostic analysis and numerical simulation were performed to investigate the characteristics and mechanism underlying the rapid weakening of typhoon Xangsane.The results show that a sharp decline in the intensity of typhoon Xangsane resulted from its movement into the cool sea surface temperature area in the East China Sea,the intrusion of cold air from the mainland into the typhoon,and a rapid increase of the vertical wind shear in the surrounding environment.An important factor that led to the demise of the typhoon was a significant decrease in the moisture transport into the typhoon.Furthermore,the results of the numerical simulation and sensitivity experiments indicate that sea surface temperature largely modulated the rapid weakening of typhoon Xangsane.     

环境场对近海热带气旋突然增强与突然减弱影响的对比分析

采用动态合成分析法对近海突然加强(RITC)和突然减弱(RWTC)两类热带气旋(TC)的环境场进行对比分析。研究表明:(1)两类TC形势场差异较明显,且影响RITC的南亚高压比影响RWTC的南亚高压强。(2)突变前后RITC有充足水汽供应配合较强辐合及上升运动,TC不断获得水汽凝结释放的潜热,使得损耗的能量得到补充和加强,高层辐散突变后减弱,使得TC能量得以保存和聚集,暖心结构被不断增加的潜热能所加强,有利于TC强度的爆发。(3)RWTC突变前后中低层上升运动减弱,中低层辐合变化不大,且由于水汽供应不足,TC获得的凝结潜热不足以补充TC自身的能量损耗,并且高层的上升运动及辐散突变后均加强,这些均有利于TC中心高层暖心热量不断减少,从而促使TC强度快速减弱。     

广州市雷暴日异常的基本气候特征及其与近海海温关系初探

分析了广州市雷暴日变化的基本气候特征。结果表明:广州市雷暴日主要集中在5～8月,占全年雷暴日总量的71.38%,雷暴日的季节分布具有双峰型的特征。近48年以来广州市雷暴日呈明显的下降趋势。广州市5～8月的雷暴日与同期850hPa大气环流的关系:多雷暴年整个亚洲中纬地区(35N)有明显的偏西风距平,南海及广东以及向北延伸的广大地区的西南及偏南气流盛行,少雷暴年则刚好相反。与近海海温做了简单的相关分析,得出:广州市雷暴日与前期4～6月印尼附近西太平洋海温呈负相关的变化趋势。     

华南地区热带气旋登陆前强度突变的大尺度环境诊断分析

利用每6小时一次的NCEP再分析资料,对华南地区登陆前突然减弱和突然增强的两类热带气旋（TC）进行大尺度诊断分析,结果表明：（1）突然增强的TC位于副高的西南侧或南侧,低空有明显的西南气流卷入TC内部,而突然减弱的TC基本在副高西侧或西北侧;（2）突然增强TC的低空辐合、高空辐散均较强;（3）充足的水汽输送是TC登陆前突然增强的另一重要原因。     

COMPARATIVE ANALYSIS OF THE INTENSITY AND DISTRIBUTION OF HEAVY RAINS IN ZHEJIANG PROVINCE CAUSED BY TYPHOONS HAITANG AND MATSA

Study was carried out on two landfall typhoons Haitang and Matsa, which affected Zhejiang province seriously in 2005. Firstly, the similarity and difference between the two typhoon-induced heavy rains were compared and it was pointed out that both of them brought strong large-scale precipitation and the maximum centers of rainfall were located on the north side of the landfall site. Making landfall on Fujian, Haitang was weaker than Matsa in intensity but surpassed it in rainfall. Then with focus on intensity, moving speed, structure of typhoon, circulation and terrain, the two typhoon-related heavy rains were compared and analyzed. Results show that the asymmetrical distribution of rainfall was closely related to the structure of typhoons themselves, moisture transportation and mesoscale terrain. In contrast to the south side, the north side was hotter and wetter and water vapor was also more abundant. The phenomenon of more rainfall induced by Haitang was in connection with the following reasons. Invading cold air led to rainfall increases, weakened dynamic field and slower movement both benefited precipitation. For the last part, the cold characteristic of air mass over Zhejiang was also a favorable factor for the rain.     

我国热带气旋登陆时间日变化特征分析

利用1949～1999年<热带气旋年鉴>所给出的有关资料,分析了热带气旋登陆我国时间的变化特征.结果显示登陆时间具有某些日变化特征.就全国而言,登陆时间在夜晚和上午时段的出现频率较大,凌晨04～07时和下午13～18时出现频率较小.这一出现频率的日变化分布特征在广东表现得最为明显,登陆我国其它地区的时间日变化不明显.分析表明,较弱的热带气旋、登陆过程中强度减弱的热带气旋的登陆时间具有显著的日变化特征.     

强台风“黑格比”实测海上风电机组极端风况特征参数分析和讨论

利用广东近海海上一座100 m高气象塔上设置的三维超声测风仪获取的强台风“黑格比”过程实测数据，分析研究海上风电机组在强台风影响下极端载荷参数的变化特征，通过仪器直接测量的参数与IEC 61400-1规范(由国际电工委员会制定)推荐方法计算结果的对比，研究该规范推荐的风电机组极端载荷参数计算方法在台风条件下的适用性。研究结果表明：(1) 强台风“黑格比”在近海海面上产生的极端操作阵风风速和极端风向变幅的过程变化均呈“M”型双峰分布，最大值均出现在台风眼壁强风区；(2) 由仪器直接测量的极端操作阵风风速和极端风向变幅值与根据IEC公式计算结果差别明显；(3) 台风强风影响产生的极端操作阵风和极端风向变幅参数均出现超越IEC给出的三种标准类型风电机组的设计上限标准；并且IEC公式计算值比仪器直接测量值显著偏大；(4) 在风电机组处于满发、切出和停机生存等工况下，IEC公式计算和仪器直接测量的极端操作阵风基本一致，但IEC公式对极端风向变幅的计算值要比仪器直接测量值大。与IEC的风电机组设计标准相比，仪器直接测量的极端操作阵风在时间周期1～3.5 s和7～10 s区间超出标准，但极端风向变幅一般不会突破IEC的风电机组设计标准。     

A CLIMATOLOGY OF DEEP CONVECTION OVER SOUTH CHINA AND THE ADJACENT WATERS DURING SUMMER

Due to the higher temporal and spatial resolution and the better integrality of long-term satellite infrared(IR) Brightness Temperature(TBB) data,a climatology of deep convection during summer over South China and the adjacent waters is presented in this paper based on the 1-hourly infrared IR TBB data during June-August of 1996-2007(except 2004).The results show that the geographic distribution of deep convection denoted by TBB ≤-52℃ over South China and the adjacent waters are basically consistent with previous statistical results based on surface thunderstorm observations and low-orbit satellite lightning observations.The monthly,ten-day,five-day and diurnal variations of deep convection in this region are focused on in this paper.There are 5 active deep-convection areas in June-August.The monthly variations of the deep convection are closely associated with the large-scale atmospheric circulations.The deep convection over the land areas of South China is more active in June while that over the South China Sea is more active in July and August.The development of deep convection is prominently intermittent and its period is about 3 to 5 five-day periods.However,the deep convection over the coastal areas in South China remains more active during summer and has no apparent intermittence.The ten-day and five-day variations of deep convection show that there are different variations of deep convection over different areas in South China and the adjacent waters.The tendency of deep convection over the land areas of South China is negatively correlated with that over the South China Sea.The diurnal variations of deep convection show that the sea-land breeze,caused by the thermal differences between land and sea,and the mountain-valley breeze,caused by the thermal differences between mountains and plains or basins,cause deep convection to propagate from sea to land in the afternoon and from land to sea after midnight,and the convection over mountains propagates from mountains to plains after midnight.The different diurnal variations of deep convection over different underlying surfaces show that not only there are general mountainous,marine and multi-peak deep convection,but also there is longer-duration deep convection over coastal areas and other deep convection triggered and maintained by larger-scale weather systems in South China during summer.     

中国草坪气候区划探讨

根据草坪草的气候生态适应性,分别确定了冷地型草坪草和暖地型草坪草的农业气候指标,在全国范围内选取85个站点,按照7个农业气候指标,运用聚类分析进行了气候区域的划分,并对各区草坪草的选择、繁殖和杂草防治等技术关键进行了评述。