中国近几年热带气旋研究进展

总结了中国过去几年尤其是“八五”结束后热带气旋领域取得的研究成果。主要包括以下几个方面的内容：热带气旋的结构、数值预报研究、业务数值预报评估、热带气旋暴雨、热带气旋的气候特征以及热带气旋的灾害等等。     

沙漠气象若干问题研究进展

沙漠占据地球陆地面积的1/4,沙漠天气和气候对全球生态、环境及气候等的影响一直都受到社会各界极大关注。本文参考国内外有关沙漠气象学研究的代表性著作,简要回顾了沙漠气象学的国内外发展历史,并从沙漠表层物理特性研究、沙漠天气与边界层研究、沙漠气候研究、沙漠影响区域及全球环境研究等多个方面阐述了沙漠气象学的研究进展。最后对沙漠气象学研究提出了展望。     

热带气旋闪电活动特征研究综述

针对热带气旋（tropical cyclone,TC）闪电已有研究,首先从闪电活动分布特征、眼壁闪电爆发对TC强度和路径的指示、外雨带闪电活动与雨带对流结构的关系三个方面进行了总结;其次从动力一微物理方面对TC闪电的形成原因和特征机理进行了梳理;最后提出当前研究中存在的两个关键问题,并对后续研究内容进行了展望。基于地基和空基相结合的综合闪电探测得到的闪电属性特征参量,有望建立一个明确的、具有代表性的闪电活动一TC强度变化关系。利用沿海地区架设的三维闪电定位系统结合地基双偏振霄达,针对登陆台风强对流过程开展的综合观测研究,将有助于推进闪电观测资料在台风中小尺度强对流监测、预警和资料同化中的应用。     

我国热带气旋研究十年进展

为了研究、揭示超低空急流与地形作用对暴雨的增幅机制,以2021年7月14日夜间发生在辽宁东部长白山地区的一次山地突发性暴雨为例,利用辽宁省地面观测降水数据和ERA5再分析数据,针对超低空急流形成的爬流及绕流对此次暴雨的影响进行研究,结果表明：(1) 在东北冷涡东南部、副热带高压后部的有利环流背景下,偏南低空、超低空急流建立,为辽宁东部带来充沛的水汽和能量,降水的阶段性变化与低空急流的强度、位置、方向存在一定关系。(2) 山地与平原过渡区的地形高度差强迫气流产生爬流运动,爬流所强迫的垂直运动由下至上逐渐减弱,大值区位于山地坡面上,山地区域爬流极值中心处于雨带中心位置,地形的爬流运动对降水范围及强度至关重要。(3) 以东西方向为主导的绕流对暴雨区域局地涡旋的形成具有一定贡献,并且绕流对暖湿气流在降水中心起到汇聚的作用,间接为空气抬升提供增幅效果。爬流、绕流共同作用下,坡地区域次级环流上升支触发对流发展,不稳定能量释放,导致山区局地大暴雨的出现。

     

Variation of the monsoon trough intensity in the South China Sea and western North Pacific ocean and its relationship to tropical cyclone activities

Using the daily average of the NCEP/DOE AMIP-II reanalysis data from 1979 to 2005 and the characteristics of monsoon troughs in the western North Pacific,we established an intensity index and a location index to describe the activity of the monsoon troughs in three different regions and their impacts on tropical cyclones generated therein(MTTCs).The behavior of the monsoon troughs was analyzed.The following conclusions are obtained:(1)The established monsoon trough intensity index has a positive correlation to the location index,indicating that stronger monsoon trough intensity corresponds to more northward location.(2)Monsoon trough intensity exhibits significant interannual variation,with obvious periods of 4–5 years prior to 1994 and 2–3 years afterwards.(3)The affecting factors on monsoon trough intensity are different with areas.The preceding SST anomaly results in anomalous atmospheric circulation, leading to the anomaly of monsoon trough intensity in different areas.(4)The frequency of cyclogenesis and location anomalies of the MTTC are closely related to the intensity and location of the monsoon trough. Most of the anomalously less MTTC years coincide with the years with a weak general monsoon trough and weak regional monsoon troughs.The anomalously more MTTC years are associated with both a strong general monsoon trough and a weak general monsoon trough combined with a strong one over the South China Sea,though with a larger probability for the latter.(5)The interseasonal variation of the intensity of monsoon troughs provides favorable conditions for TC generation and development.The monsoon trough is in the active periods of both quasi-biweekly 10 to 20 day and 30 to 60 day oscillations,which is favorable for MTTC occurrence.     

北上热带气旋气候特征分析

北上热带气旋是影响我国华北和东北地区的重要天气系统,其带来的大风和暴雨,常常造成我国北方地区的风灾和水灾。利用建国以来56 a的气象资料,对影响我国的北上热带气旋进行气候分析。结果表明:从时间上看,平均每年约有3个北上热带气旋,最早出现在5月下旬,最晚出现在11月中旬,其中以7月和8月为最多;每年6—9月为北上热带气旋登陆季节,7月和8月登陆的热带气旋占85%。从强度上看,能够到达北方的热带气旋一般都是较强的热带气旋,在进入北上热带气旋定义区后,总体强度明显减弱,但在进入黄渤海时仍能够达到台风的强度;与北上热带气旋相比,北上登陆热带气旋的强度更大。统计分析发现,在辽宁和华北登陆的热带气旋,其强度大于在山东半岛登陆的热带气旋。北上登陆热带气旋和北转向、中转向的热带气旋一般均能产生暴雨和大风。     

An Overview of Research and Forecasting on Rainfall Associated with Landfalling Tropical Cyclones

The ability to forecast heavy rainfall associated with landfalling tropical cyclones (LTCs) can be improved with a better understanding of the mechanism of rainfall rates and distributions of LTCs. Research in the area of LTCs has shown that associated heavy rainfall is related closely to mechanisms such as moisture transport, extratropical transition (ET), interaction with monsoon surge, land surface processes or topographic effects, mesoscale convective system activities within the LTC, and boundary layer energy transfer etc.. LTCs interacting with environmental weather systems, especially the westerly trough and mei-yu front, could change the rainfall rate and distribution associated with these mid-latitude weather systems. Recently improved technologies have contributed to advancements within the areas of quantitative precipitation estimation (QPE) and quantitative precipitation forecasting (QPF). More specifically, progress has been due primarily to remote sensing observations and mesoscale numerical models which incorporate advanced assimilation techniques. Such progress may provide the tools necessary to improve rainfall forecasting techniques associated with LTCs in the future.     

2010年和1998年西北太平洋热带气旋频数异常与东亚夏季风系统的关联性分析

利用西北太平洋编号台风资料、NCEP/NCAR再分析资料和NOAA向外长波辐射(outgoing longwave radiation,OLR)资料等,选取西北太平洋热带气旋频数异常偏少的2010年和1998年,诊断分析ENSO事件及其东亚夏季风环流异常与热带气旋频数异常的关系,给出东亚夏季风系统部分成员影响热带气旋频数的天气学图像:由春入夏,赤道东太平洋海温异常偏暖,赤道哈得来环流偏强,沃克环流偏弱;西太平洋副热带高压异常强大,位置偏西;季风槽位置偏南,东西向不发展;南海、西太平洋越赤道气流偏弱;异常热源和水汽汇偏南,南海和菲律宾以东地区对流活动受到抑制,热带对流活跃区位于赤道以南;热带气旋生成个数明显偏少,位置偏西。     

Sensitivity of tropical cyclone intensification to inner-core structure

In this study, the dependence of tropical cyclone (TC) development on the inner-core structure of the parent vortex is examined using a pair of idealized numerical simulations. It is found that the radial profile of inner-core relative vorticity may have a great impact on its subsequent development. For a system with a larger inner-core relative vorticity/inertial stability, the conversion ratio of the diabatic heating to kinetic energy is greater. Furthermore, the behavior of the convective vorticity eddies is likely modulated by the system-scale circulation. For a parent vortex with a relatively higher inner-core vorticity and larger negative radial vorticity gradient, convective eddy formation and radially inward propagation is promoted through vorticity segregation. This provides a greater potential for these small-scale convective cells to self-organize into a mesoscale inner-core structure in the TC. In turn, convectively induced diabatic heating that is close to the center, along with higher inertial stability, efficiently enhances system-scale secondary circulation. This study provides a solid basis for further research into how the initial structure of a TC influences storm dynamics and thermodynamics.     

大气季节内振荡对热带气旋活动影响的研究进展

近30年来，大气季节内振荡对热带气旋活动影响的研究已逐渐成为人们关注的焦点，并取得了显著的进展。就大气季节内振荡对热带气旋生成、路径及登陆的影响进行概述，并揭示了这种影响的主要机制。同时回顾了与季节内振荡密切相关的季风槽活动对热带气旋的影响。在此基础上简单讨论了该领域中存在的问题及未来研究前景，并提出当前该研究领域中一些亟需研究的科学问题。     

热带气旋复杂程度的分形维数表征

应用2006-2010年69个热带气旋1 295个时次的红外云图等资料,提取了1 295个TC的外缘线,用圆规法计算了这些外缘线的分形维数。将这1 295个分形维数自小到大排列,按等频数规则,将1 295个数分为5类,分别记为A、B、C、D、E类。A、B、C、D、E类分形维数的均值分别为1.21、1.26、1.29、1.33、1.40。然后寻找与这5个均值最接近的样本。这5个样本的红外云图和TBB等值线分布图显示:随着分形维数的加大,边缘线的非光滑程度逐渐加大,图形与准圆形的偏离程度逐渐加大,TC空间结构的复杂程度也逐渐加大。说明外缘线的分形维数可以在一定程度上定量表征TC的复杂程度。     

西北太平洋热带气旋频数及生成位置的气候变化研究进展

自20世纪70年代末期以来,西北太平洋的热带气旋在全球变暖的背景下主要发生了两种宏观的气候变化：一个是热带气旋生成频数呈现年代际减少,尤其是在东南部海域;另一个则是其生成与活动位置等总体特征有向西北偏移的趋势。本文对这两个方面的研究进展进行了概述。近些年的研究表明,垂直风切变的增强可能是夏秋季热带气旋频数减少的最主要原因,这与太平洋-印度洋海面温度变化导致的大尺度环境变化有密切联系。同样有研究认为北大西洋海面温度的多年代际振荡对近期西北太平洋热带气旋生成频数的减少也非常重要。但西北太平洋西部强热带气旋的频数呈现出增加的趋势,这可能与东亚近海海面温度的显著升高有关,尽管这种变化是否可信仍有争议。近20年来,西北太平洋热带气旋活动普遍出现西北移倾向,包括生成位置和路径位置,这种变化可能受到了ENSO变异及20世纪90年代末期太平洋气候突变的调控。同时,热带环流的极向扩张又导致了热带气旋的有利环境向北扩张,因此西北太平洋热带气旋活动也出现极向迁移的趋势。     

西北太平洋近赤道热带气旋生成的特征分析

1979—2012年西北太平洋存在70个形成于0°～5°N的低纬度地区的热带气旋(TC),占TC总量的8%,其中达到台风等级的个数占64%。而针对此类缺少一定科氏力作用而形成的罕见TC生成的研究相对较少。本文利用JTWC的TC最佳观测资料、ERA-Interim再分析资料,以及NOAA-OISST海温资料,以西北太平洋近赤道TC为研究对象,统计诊断了其年际、年代际、季节分布特征,分析了其大尺度环境背景场,重点探讨了近赤道TC生成的影响因子。研究结果表明,近赤道TC具有明显的年际与年代际变化,并且近赤道TC具有与西北太平洋总TC恰好相反的季节变化。近赤道TC生成的大尺度环境背景场是东北冬季风与其在近赤道地区偏转形成的西北风之间的气旋性环流。对流层低层的绝对涡度动力项与对流层中层的湿度热量项是近赤道TC生成的主要贡献因子,并且相对于5°～10°N生成的TC,近赤道TC对对流层低层的正涡度与对流层中层的湿度条件的要求更高。     

登陆的0915号热带气旋\

热带气旋（TC）预报特别是强度预报是当今大气科学研究和业务预报的重点、难点问题,TC环流内部的对流系统对气旋的结构和强度变化有着十分重要的影响。利用FY-2C/2E黑体亮温（TBB）资料和NCEP分析资料,研究了2005-2012年西北太平洋热带气旋外雨带区的对流非对称分布特征,及其与环境风垂直切变和TC移动的关系。分析发现,整层风垂直切变的方向与TBB一波非对称大值区关于方位角的分布有很好的对应关系。在弱整层风垂直切变条件下（< 5 m/s）,TC移动引起的非对称摩擦效应会使对流易出现在移动方向的右前象限。在中强整层风垂直切变条件下（>5 m/s）,风切变成为影响对流非对称分布的主要因子,TC外螺旋雨带区的对流集中于顺风切方向及其左侧,对流偏离顺切变左侧的程度一方面受到TC内逆时针环流的影响,另一方面与风垂直切变的强度有关：对于发展阶段的TC,当风垂直切变增强时,一波非对称分布更加显著,切变越强,TC强度越大,外雨带区的对流越偏离顺风切左侧;对于消亡阶段的TC,风垂直切变的影响作用并不明显。     

热带气旋生成指数对印度洋热带气旋频数变化的适用性研究

本文利用ERA5 1979-2019年逐月大气再分析资料计算南北印度洋热带气旋生成指数，并和IBTrACS观测数据进行比较，探讨用热带气旋生成指数研究南北印度洋热带气旋变化特征的适用性.研究发现热带气旋生成指数能较好地刻画南北印度洋热带气旋的空间分布特征、北印度洋热带气旋个数月变化的双峰结构，以及南印度洋比北印度洋热带气旋发生概率高等特征.最新的IBTrACS v4.0观测资料显示，40年来北印度洋热带气旋每年总生成个数平均每10年增加1.3个，频数的增加主要来源于热带低压和热带风暴，而南印度洋热带气旋每年总生成个数每10年减少2.8个.热带气旋生成指数能很好地描述北印度洋热带气旋生成个数的上升趋势，但对南印度洋热带气旋生成个数趋势的刻画与观测不一致，可能原因需要进一步深入研究.     

Ensemble Forecasting of Tropical Cyclone Motion Using a Baroclinic Model

The purpose of this study is to investigate the effectiveness of two different ensemble forecasting (EF) techniques–the lagged-averaged forecast (LAF) and the breeding of growing modes (BGM). In the BGM experiments, the vortex and the environment are perturbed separately (named BGMV and BGME). Tropical cyclone (TC) motions in two difficult situations are studied: a large vortex interacting with its environment, and an apparent binary interaction. The former is Typhoon Yancy and the latter involves Typhoon Ed and super Typhoon Flo, all occurring during the Tropical Cyclone Motion Experiment TCM- 90. The model used is the baroclinic model of the University of New South Wales. The lateral boundary tendencies are computed from atmospheric analysis data. Only the relative skill of the ensemble forecast mean over the control run is used to evaluate the effectiveness of the EF methods, although the EF technique is also used to quantify forecast uncertainty in some studies. In the case of Yancy, the ensemble mean forecasts of each of the three methodologies are better than that of the control, with LAF being the best. The mean track of the LAF is close to the best track, and it predicts landfall over Taiwan. The improvements in LAF and the full BGM where both the environment and vortex are perturbed suggest the importance of combining the perturbation of the vortex and environment when the interaction between the two is appreciable. In the binary interaction case of Ed and Flo, the forecasts of Ed appear to be insensitive to perturbations of the environment and/or the vortex, which apparently results from erroneous forecasts by the model of the interaction between the subtropical ridge and Ed, as well as from the interaction between the two typhoons, thus reducing the effectiveness of the EF technique. This conclusion is reached through sensitivity experiments on the domain of the model and by adding or eliminating certain features in the model atmosphere. Nevertheless, the forecast tracks in some of the cases are improved over that of the control. On the other hand, the EF technique has little impact on the forecasts of Flo because the control forecast is already very close to the best track. The study provides a basis for the future development of the EF technique. The limitations of this study are also addressed. For example, the above results are based on a small sample, and the study is actually a simulation, which is different than operational forecasting. Further tests of these EF techniques are proposed.     

Boundary-layer wind structure in a landfalling tropical cyclone

In this study, a slab boundary layer model with a constant depth is used to analyze the boundary-layer wind structure in a landfalling tropical cyclone. Asymmetry is found in both the tangential and radial components of horizontal wind in the tropical cyclone boundary layer at landfall. For a steady tropical cyclone on a straight coastline at landfall, the magnitude of the radial component is greater in the offshoreflow side and the tangential component is greater over the sea, slightly offshore, therefore the greater total wind speed occurs in the offshore-flow side over the sea. The budget analysis suggests that： （1） a greater surface friction over land produces a greater inflow and the nonlinear effect advects the maximum inflow downstream, and （2） a smaller surface friction over the sea makes the decrease of the tangential wind component less than that over land. Moreover, the boundary layer wind structures in a tropical cyclone are related to the locations of the tropical cyclone relative to the coastline due to the different surface frictions. During tropical cyclone landfall, the impact of rough terrain on the cyclone increases, so the magnitude of the radial component of wind speed increases in the offshore-flow side and the tangential component outside the radius of maximum wind speed decreases gradually.     

Simulation of the Electrification of a Tropical Cyclone Using the WRF-ARW Model：An Idealized Case

Evolution of the electrifi cation of an idealized tropical cyclone （TC） is simulated by using the Advanced Weather Research and Forecasting （WRF-ARW） model. The model was modifi ed by addition of explicit electrifi cation and a new bulk discharge scheme. The characteristics of TC lightning is further examined by analyses of the electrifi cation and the charge structure of the TC. The fi ndings thus obtained are able to unify most of the previous inconsisitent observational and simulation studies. The results indicate that the TC eyewall generally exhibits an inverted dipole charge structure with negative charge above the positive. In the intensifi cation stage, however, the extremely tall towers of the eyewall may exhibit a normal tripole structure with a main negative region between two regions of positive charge. The outer spiral rainband cells display a simple normal dipole structure during all the stages. It is further found that the diff erences in the charge structure are associated with diff erent updrafts and particle distributions. Weak updrafts, together with a coexistence region of diff erent particles at lower levels in the eyewall, result in charging processes that occur mainly in the positive graupel charging zone （PGCZ）. In the intensifi cation stage, the occurrence of charging processes in both positive and negative graupel charging zones is associated with strong updraft in the extremely tall towers. In addition, the coexistence region of graupel and ice crystals is mainly situated at upper levels in the outer rainband, so the charging processes mainly occur in the negative graupel charging zone （NGCZ）.     

夏季热带北大西洋海温异常对西北太平洋热带气旋生成的影响

利用1979—2012年西北太平洋热带气旋最佳路径资料,Hadley中心的海温资料和NCEP/NCAR再分析资料等,研究了夏季(6—10月)热带北大西洋海温异常与西北太平洋热带气旋(Tropical Cyclone,TC)生成的关系及其可能机制。结果表明,夏季热带北大西洋海温异常与同期西北太平洋TC生成频次之间存在显著的负相关关系。热带北大西洋海温的异常增暖可产生一对东—西向分布的偶极型低层异常环流,其中气旋性异常环流位于北大西洋/东太平洋地区,反气旋异常环流位于西北太平洋地区。该反气旋环流异常使得TC主要生成区的对流活动受到抑制、低层涡度正异常、中低层相对湿度负异常、中层下沉气流异常,这些动力/热力条件均不利于TC生成。此外,西北太平洋地区低层涡旋动能负异常,同时来自大尺度环流的涡旋动能的正压转换也受到抑制,不能为TC的生成和发展提供额外能量源。反之亦然。     

热带季节内振荡与影响广西的热带气旋生成发展的联系

利用1978-2013年美国NOAA逐候MJO指数和中国气象局上海台风研究所热带气旋资料,研究了MJO与影响广西热带气旋发生发展的联系。结果表明,当MJO处于非洲大陆和西印度洋时,热带气旋生成区域上空为异常东风带;而当MJO处于西太平洋时,热带气旋生成区域北侧为东风异常带、南侧为西风异常带,有利于季风槽或气旋性环流加强,导致影响广西热带气旋频数偏多。当MJO处于东印度洋时,南海上空风场存在明显的向南分量,热带气旋生成数少、位置偏南;而当MJO处于东太平洋时,热带西太平洋对流受到抑制,导致影响广西热带气旋偏少。