南海灾害性土台风统计分析

根据台风年鉴资料统计分析了南海热带气旋(指在南海海域生成的热带气旋、又称南海灾害性土台风、下面简称TC)，TC数量逐年逐月变化较大，除3月没有TC出现外，其余月份均有TC出现，年生成最多的TC为11个，最少的为1个，年平均6．2个，月生成最多的TC为5个，最少的为零个。TC登陆最多的是8月，12月至翌年4月没有TC登陆中国大陆，登陆范围主要在汕头至海南岛之间。TC的持久期一般均在4—7天，最长亦有19天。南海上生成的TC只有15％能够加强为台风，均集中在水深超过150米的海域。南海是TC发生频繁、数量较多的海域。     

A COMPREHENSIVE ANALYSIS OF INTERACTIONS BETWEEN MESOSCALE CONVECTIVE CLOUD CLUSTERS IN TYPHOONS AND MESOSCALE HEAVY RAINS

1INTRODUCTIONHeavyrainsassociatedwithtyphoonsareoneoftheimportantmeteorologicaldisastersintheFujianProvince,whichbringsaboutgreaterdamageinshort-lived,severeprecipitation.Muchdocumentationhasbeenreportedonthestudyofthemesoscaleconvectionsystemsandmesoscaleconvectivecomplex(MCC)andassociatedprecipitation[1-3].UsinglandfallcasesoftropicalcyclonesFrankie(No.9607),Gloria(No.9608),Joy(No.9610),Winnie(No.9714)andanunnamedtyphoon(No.9802)andhourlyinfraredcloudimagery,thecurrentworkstudiesth…     

双台风“纳沙”和“海棠”登陆后强度变化成因及对比分析

利用NCEP（National Centers for Environmental Prediction）再分析资料对2017年双台风“纳沙”（1709）和“海棠”（1710）先后登陆福建后的强度变化特征进行对比分析。结果表明：低纬水汽输送的强弱变化是造成双台风强度变化的主要原因,而越赤道气流对水汽输送起到关键作用。副热带西风急流与中低空风场强弱变化一致,西风急流增强伴随中低空东风加强是“海棠”陆上强度维持不减的原因之一,反之“纳沙”快速减弱。双台风效应对强度变化也起着重要作用：双台风靠近相吸作用下,“纳沙”残余环流卷入“海棠”环流中,为其输送正涡度因子及斜压能量,也是促使“海棠”强度维持的原因。台风登陆后,其上空三种不同层差的垂直风切变值表现一致减小的变化趋势及低于6 m·s^-1的风切,有利于弱台“海棠”陆上长久维持。海岸锋生及海表通量动热力因子对“海棠”右侧中小尺度对流发展和维持起到重要作用,加剧了“海棠”非对称性结构,促使“海棠”强度维持不减。     

ANALYSIS ON WAVELET POWER SPECTRUM OF WARM AND COLD EVENTS IN THE NI(N)O REGIONS

We statistically analyze the tropical typhoon forming in the South China Sea and use TC (Tropical Cyclone) for short in the following) by typhoon yearbook. The typhoon quantity is very different in different months and years. TC appears in all months except March, and the most TC quantity in a year is 11, the least is 1 and 6.2 on average. The most TC quantity in a month is 5 and the least is 0. TC lands most in August and no TC lands on Chinese continent from December to the following April. The primary landing area is between Shantou and Hainan Island. The sustaining period of TC is usually between 4 days to 7days, and the longest is 19 days.Only 15% of the TC forming in the South China Sea can intensify to typhoon, and they all form in the ocean area deeper than 150m. The South China Sea is the ocean area over which the TC occurs frequently.     

Tropical Cyclones and Polar Lows: Velocity, Size,and Energy Scales, and Relation to the 26°C Cyclone Origin Criteria

The goal of this paper is to quantitatively formulate some necessary conditions for the development of intense atmospheric vortices. Specifically, these criteria are discussed for tropical cyclones (TC) and polar lows (PL) by using bulk formulas for fluxes of momentum, sensible heating, and latent heating between the ocean and the atmosphere. The velocity scale is used in two forms: (1) as expressed through the buoyancy flux b and the Coriolis parameter lc for rotating fluids convection, and (2) as expressed with the cube of velocity times the drag coefficient through the formula for total kinetic energy dissipation in the atmospheric boundary layer. In the quasistationary case the dissipation equals the generation of the energy. In both cases the velocity scale can be expressed through temperature and humidity differences between the ocean and the atmosphere in terms of the reduced gravity, and both forms produce quite comparable velocity scales. Using parameters b and lc., we can form scales of the area and, by adding the mass of a unit air column, a scale of the total kinetic energy as well. These scales nicely explain the much smaller size of a PL, as compared to a TC, and the total kinetic energy of a TC is of the order 1018 - 1019 J. It will be shown that wind of 33 m s-1 is produced when the total enthalpy fluxes between the ocean and the atmosphere are about 700 W m-2 for a TC and 1700 W m-2 for a PL, in association with the much larger role of the latent heat in the first case and the stricter geostrophic constraints and larger static stability in the second case. This replaces the mystical role of 26~C as a criterion for TC origin. The buoyancy flux, a product of the reduced gravity and the wind speed, together with the atmospheric static stability, determines the rate of the penetrating convection. It is known from the observations that the formation time for a PL reaching an altitude of 5-6 km can be only a few hours, and a day, or even half a day, for a TC reaching 15-18 km. These two facts allow us to construct curves on the plane of Ts and △T= Ts - Ta to determine possibilities for forming an intense vortex. Here, Ta is the atmospheric temperature at the height z = 10 m. A PL should have △T > 20℃ in accordance with the observations and numerical simulations. The conditions for a TC are not so straightforward but our diagram shows that the temperature difference of a few degrees, or possibly even a fraction of a degree, might be sufficient for TC development for a range of static stabilities and development times.     

ENTROPY FLOW CHARACTERISTICS ANALYSIS OF TYPHOON MATSA (0509)

The evolution of Typhoon Matsa (0509) is examined in terms of entropy flow through an entropy balance equation derived from the Gibbs relation, according to the second law of thermodynamics. The entropy flows in the various significant stages of (genesis, development and decaying) during its evolution are diagnosed based on the outputs of the PSU/NCAR mesoscale model (known as MM5). The results show that: (1) the vertical spatial distribution of entropy flow for Matsa is characterized by a predominantly negative entropy flow in a large portion of the troposphere and a positive flow in the upper levels; (2) the fields of entropy flows at the middle troposphere (500 hPa) show that the growth of the typhoon is greatly dependent on the negative entropy flows from its surroundings; and (3) the simulated centres of heavy rainfall associated with the typhoon match well with the zones of large negative entropy flows, suggesting that they may be a significant indicator for severe weather events.     

影响中国台风的气候特征及其与环境场关系的研究

分析了影响中国台风的气候特征,结果表明：5-11月是影响台风活跃季节,7-9月为集中期;1951—2004年影响台风的频数变化呈减少趋势,1970年代后期明显减少,近十年是影响台风频数最少的时期;近50余年影响台风中超强台风的频数减少显著;台风生成的源地有明显的年代际变化,1960年代-1970年代生成台风位置偏东、偏南,1980年代以后转为偏北、偏西。同时分析了影响台风与北太平洋海温及东亚夏季风环流的关系,认为北太平洋海温的年代际和年际变化与影响台风关系密切;影响台风偏多年和偏少年,其环流形势截然不同。     

多普勒雷达资料在近海强台风模拟中的同化试验

利用中尺度数值模式(WRF),并同化了多普勒雷达反射率和径向速度资料以及非常规的观测资料,对近几年登陆于浙闽沿海的4例强台风进行了数值模拟。通过高时空分辨率的模拟结果对比分析表明:雷达资料的同化,对近海登陆台风路径和降水模拟以及中尺度降水特征都有进一步改进的效果;模拟较好的揭示了台风近中心螺旋云带中的强中尺度对流系统。通过模拟分析表明,在台风近中心的螺旋云带中,低层有一条强辐合线存在,它与实况多普勒雷达给出的低层平显(PPI)强度回波带有较好的对应关系,也与沿海地区中尺度暴雨系统紧密联系,并由此看到近海海域降水带和强对流区的存在。     

台风"莫拉克"路径诊断分析和模拟

利用客观分析资料和数值模拟方法分析了0908号台风"莫拉克"穿越台湾岛前后在路径上出现的北翘、西折现象以及进入台湾海峡后移动异常缓慢的原因.结果表明:①台风靠近台湾岛后西太平洋副高减弱东撤,引导气流明显减弱,台风减速;台风进入台湾海峡后,北侧高压带的断裂和随后的重新连接加强是其路径偏北转向和移动缓慢的主因.②"莫拉克"...     

“23·7”华北特大暴雨过程的水汽特征

基于常规地面和探空观测以及ERA5再分析资料,分析了2023年7月29日至8月1日华北特大暴雨过程（简称“23·7”过程）的水汽输送、收支及其极端性等特征,探讨了太行山地形对持续性水汽辐合与垂直输送的重要作用。结果表明：此次过程发生在台风杜苏芮残涡北上,受高压坝阻挡,并有双台风（杜苏芮、卡努）水汽输送的有利背景下,降水时间超长、日降水量和累计降水量极大,在华北地区均有显著极端性。低层强盛的东南急流源源不断向华北地区输送水汽,暴雨区南边界和东边界均为水汽净流入,尤以南边界为主。偏东风在太行山东麓地形高度梯度区强迫抬升,形成强的水汽辐合与垂直输送中心,并稳定维持,是造成此次特大暴雨的重要原因。持续的水汽输送与辐合使得整层可降水量最大值超过75 mm,距平超过气候平均3个标准差,具有较强的极端性。对比“23·7”过程与2016年7月19—20日华北特大暴雨过程的水汽特征发现,二者低层水汽来源不同,前者主要来自西北太平洋和我国南海,后者则主要来自我国南海和孟加拉湾;前者区域平均水汽辐合强度明显弱于后者,单位时间内较强的短时强降水站次亦少于后者,但影响时间长于后者,说明相较于雨强而言,超长的降水时间是产生“23·7”极端强降水更为关键的因素。