Effect of the Vertical Diffusion of Moisture in the Planetary Boundary Layer on an Idealized Tropical Cyclone

Previous numerical studies have focused on the combined effect of momentum and scalar eddy diffusivity on the intensity and structure of tropical cyclones. The separate impact of eddy diffusivity estimated by planetary boundary layer(PBL) parameterization on the tropical cyclones has not yet been systematically examined. We have examined the impacts of eddy diffusion of moisture on idealized tropical cyclones using the Advanced Research Weather Research and Forecasting model with the Yonsei University PBL scheme. Our results show nonlinear effects of moisture eddy diffusivity on the simulation of idealized tropical cyclones. Increasing the eddy diffusion of moisture increases the moisture content of the PBL, with three different effects on tropical cyclones:(1) an decrease in the depth of the PBL;(2) an increase in convection in the inner rain band and eyewall; and(3) drying of the lowest region of the PBL and then increasing the surface latent heat flux. These three processes have different effects on the intensity and structure of the tropical cyclone through various physical mechanisms. The increased surface latent heat flux is mainly responsible for the decrease in pressure. Results show that moisture eddy diffusivity has clear effects on the pressure in tropical cyclones, but contributes little to the intensity of wind. This largely influences the wind–pressure relationship, which is crucial in tropical cyclones simulation. These results improve our understanding of moisture eddy diffusivity in the PBL and its influence on tropical cyclones, and provides guidance for interpreting the variation of moisture in the PBL for tropical cyclone simulations.     

Intraseasonal modulation of tropical cyclogenesis in the western North Pacific: a case study

The temporal clustering of the western North Pacific tropical cyclogenesis and its modulation by the Madden–Julian oscillation (MJO) during the 1991 summer were examined based on the tropical cyclone best track, outgoing longwave radiation, and NCEP/NCAR reanalysis datasets. The wavelet analysis shows that convective activities around the monsoon trough in the western North Pacific possessed a distinct MJO with a period of 20–60 days. Two or more tropical cyclones were observed to form successively during each active phase of the MJO, and tropical cyclones tended to generate around the southeastern part of the maximum vorticity of the low-frequency cyclonic circulation during the developing and peak stages of the active MJO phase. But tropical cyclogenesis scarcely occurred during inactive MJO phases. Thus the MJO was a major agent in modulating repeated development of tropical cyclones in the western North Pacific during the 1991 summer. The MJO in circulation was characterized by a huge anomalous cyclone (anticyclone) in the lower troposphere existing alternately over the western North Pacific, leading to an enhanced (weakened) monsoon trough. An examination of the meridional gradient of absolute vorticity associated with the zonal flow indicates that the zonal flow in the monsoon trough region satisfied the necessary conditions for barotropic instability, with both zonal flow and the meridional gradient of absolute vorticity varying on the similar MJO timescale. The intraseasonal oscillation of such an unstable zonal flow might thus be an important mechanism for temporal clustering of tropical cyclogenesis in the western North Pacific. The barotropic conversion could provide a major energy source for the formation and growth of tropical cyclones in the western North Pacific during active MJO phases, with the eddy kinetic energy generation being dominated by both terms of eddies interacting with zonal and meridional gradients of the basic zonal flow.     

目标圆方法在船舶导航中的应用

根据多年指挥海上船舶绕避热带气旋的经验,提出了一种基于热带气旋预报目标圆的绕避热带气旋方法。文中给出了目标圆方法的基本原理、操作流程和关键技术,介绍了实际使用此方法成功指挥船舶绕避热带气旋的实例。统计结果表明,近年来此方法的使用效果和效益评估情况良好,具有较高的使用价值。这种绕避热带气旋的方法同样适用于船舶绕避爆发性气旋。     

The Impact of Land-Surface Parameter Properties and Resolution on the Simulated Cloud-Topped Atmospheric Boundary Layer

A method to simulate characteristics of wind speed in the boundary layer of tropical cyclones in an idealized manner is developed and evaluated. The method can be used in a single-column modelling set-up with a planetary boundary-layer parametrization, or within large-eddy simulations (LES). The key step is to include terms in the horizontal velocity equations representing advection and centrifugal acceleration in tropical cyclones that occurs on scales larger than the domain size. Compared to other recently developed methods, which require two input parameters (a reference wind speed, and radius from the centre of a tropical cyclone) this new method also requires a third input parameter: the radial gradient of reference wind speed. With the new method, simulated wind profiles are similar to composite profiles from dropsonde observations; in contrast, a classic Ekman-type method tends to overpredict inflow-layer depth and magnitude, and two recently developed methods for tropical cyclone environments tend to overpredict near-surface wind speed. When used in LES, the new technique produces vertical profiles of total turbulent stress and estimated eddy viscosity that are similar to values determined from low-level aircraft flights in tropical cyclones. Temporal spectra from LES produce an inertial subrange for frequencies \(\gtrsim \)0.1 Hz, but only when the horizontal grid spacing \(\lesssim \)20 m.     

Storm cyclones in the North Atlantic

Considered are long-term features and characteristics of storm activity variability in the North Atlantic based on the method of automatic identification of cyclone centers using the data on sea level pressure as well as the estimates of the maximum speed of the surface wind in the area of cyclones. Integral regional parameters of the variability of storm cyclone frequency for the gradations of the surface wind speed are presented for some areas of the North Atlantic. Investigated is the interrelation between extremely deep and storm cyclones.     

热带气旋定量降水预报的动力相似方案

该文提出一个热带气旋定量降水预报(QPF) 的动力相似方案。方案应用热带气旋初始参数、历史过程的天气形势场和物理量场及数值预报产品, 构造预报区域内当前时刻至未来时刻环境要素场的多元客观相似判据。通过定义非线性的相似指数综合评估历史热带气旋样本与预报热带气旋在多元判据下的连续动态相似程度, 以此找到相似样本。应用相似样本的历史降水量记录进行相似指数的权重综合, 得到热带气旋未来6~48 h降水量的定点、定量预报值。预报试验表明该方案具有一定的预报技巧。     

Understanding of the Effect of Climate Change on Tropical Cyclone Intensity: A Review

The effect of climate change on tropical cyclone intensity has been an important scientific issue for a few decades.Although theory and modeling suggest the intensification of tropical cyclones in a warming climate,there are uncertainties in the assessed and projected responses of tropical cyclone intensity to climate change.While a few comprehensive reviews have already provided an assessment of the effect of climate change on tropical cyclone activity including tropical cyclone intensity,this review focuses mainly on the understanding of the effect of climate change on basin-wide tropical cyclone intensity,including indices for basin-wide tropical cyclone intensity,historical datasets used for intensity trend detection,environmental control of tropical cyclone intensity,detection and simulation of tropical cyclone intensity change,and some issues on the assessment of the effect of climate change on tropical cyclone intensity.In addition to the uncertainty in the historical datasets,intertwined natural variabilities,the considerable model bias in the projected large-scale environment,and poorly simulated inner-core structures of tropical cyclones,it is suggested that factors controlling the basin-wide intensity can be different from individual tropical cyclones since the assessment of the effect of climate change treats tropical cyclones in a basin as a whole.     

登陆热带气旋长久维持与迅速消亡的大尺度环流特征

采用动态合成分析方法 ,对登陆后长久维持热带气旋 (LTC)和迅速消亡热带气旋 (STC)的大尺度环流特征进行合成分析和动力诊断。研究表明 :(1)LTC登陆后 ,在一个长波槽前有向偏北移动靠近中纬度斜压锋区的趋势 ,而STC登陆后 ,无长波槽靠近 ,并远离中纬度斜压锋区 ;(2 )LTC登陆后 ,仍与一支低空急流水汽输送通道连结 ,而STC登陆后很快与这支水汽通道分离 ;(3)LTC登陆后逐渐变性 ,获取斜压能量 ,其环境风垂直切变增强 ,Δζ2 0 0 -850负值增大 ,而STC登陆后没有这样的特征 ;(4 )LTC登陆后 ,其高层与中纬度急流靠近 ,增强了其向东北方向的高空流出气流 ,而STC不存在这样一支流出气流 ;(5 )LTC登陆后 ,摩擦使其能量耗损 ,但从中高层环境中获得了能量 ,而STC登陆后 ,有同样的能耗却无明显的环境能量补给。因此 ,当一个热带气旋登陆后 ,从其移动趋势、与水汽通道的连结、与斜压锋区的关系和高空流出气流等特征 ,可以初步判断其是长久维持还是迅速衰减。     

非均匀风场与急流强迫的水体涡旋动力特征模拟

通过数值模拟有限区域水气界面由强迫作用驱动形成的水体涡旋及环流动力结构特征,分析非均匀风场、水体急流、两者叠加以及环境边界和地转偏向力等因子的综合影响,探讨此类水体涡旋结构和动力特征。风应力驱动的水体涡旋尺度大,相对深厚,正涡旋具有下凹表面,负涡旋具有上凸表面。水体急流驱动的涡旋形成在急流两侧,对应急流所在深度及厚度尺度相对较小,也较浅,但流速与强度均大于风场驱动的涡旋环流。地形阻挡起着引导涡旋环流走向的作用;同时在北半球地转偏向力对急流侧向负涡旋形成和强度增强更为有利。此外正涡旋对应的辐合辐散势函数强于负涡旋,有利于正涡旋区垂直上升运动强于负涡旋中垂直下沉运动。非均匀风场及水体急流两种强迫叠加作用下,涡旋数量增加、尺度减小,底层的流场形态及强度与表层差异增大。形成的水体涡旋结构呈现多种形态：深厚的整层一致;浅薄的仅维持在上层,或上下层环流相反等。风应力驱动的涡旋以正压性为主,水体急流驱动的涡旋因急流的垂直强切变而具有强的斜压性,在正斜压动能的转换中,正压性涡旋区有斜压动能向正压动能转换,斜压性涡旋区有正压动能向斜压动能转换,均有利于这两个区域正负涡旋的维持。     

适用于热带气旋分析的动态合成方法

介绍跟随热带气旋的动态合成方法,可以避免把简单算术平均的合成方法用于热带气旋分析时,不可避免地会带来信息平滑的问题.该方法采用随热带气旋移动的动态坐标,热带气旋中心即为坐标的的原点,将各个样本相同坐标的格点进行算术平均即可得到动态合成场.该方法可以使热带气旋结构保持相对完整,而且热带气旋周围环流系统的相对位置也基本得到保留;并给出了一个例子说明该方法是适用于热带气旋分析的.     

广东近海台风路径异常的统计特征

对1949~2000年的52年间在广东沿海近岸转折或沿海岸移动的热带气旋异常路径进行了统计分析，同时还研究了广东沿海的地形特征。结果发现，转折点 (或靠岸点) 主要集中在有明显山脉地形的区域，同时靠岸前热带气旋有移速减慢的特征。另外还发现，转折前强度越强，则转折点离岸越近；靠岸前平均移速越小，则转折角度越大；靠岸前强度越强，则其沿海岸移动所需入射角越小。     

SVM方法在热带气旋风雨及温度预报中的应用

热带气旋的强弱和移动路径会直接影响到周围大气中气压、温度、露点等气象要素的变化.为更好地了解热带气旋对海口市的影响,通过收集影响海口市热带气旋关键因子,建立热带气旋风雨影响预报因子库,基于SVM方法对热带气旋在过程降水量、最大风速和平均温度进行趋势预报.结果表明,该方法对影响海口市热带气旋的过程降水量、最大风速和平均温度都有较好的预测效果,但对于超过15 m/s的最大风速和200 mm以上降水量级上存在一定的偏差,这可能与SVM模式中预报因子库中关键因子不全及模式的择中原理使结果趋于平均化相关.     

近71a影响黑龙江省热带气旋统计特征分析

利用中国气象局上海台风研究所整编的1949—2019年热带气旋数据,统计分析近71 a影响黑龙江省的热带气旋发生时间、频率、强度、移动路径等特征。结果表明：近71 a影响黑龙江的热带气旋共有77个,平均1.08个·a^-1,其中有28 a没有热带气旋影响黑龙江;近10 a是黑龙江受热带气旋影响的活跃期,西北太平洋生成的热带气旋频数与影响黑龙江的频数没有直接相关关系,出现El Ni1o或La Ni1a现象时对影响黑龙江的热带气旋起抑制作用;热带气旋影响黑龙江最早出现在5月,最晚出现在9月,8月出现频率最高,“七下八中下”是每年的活跃阶段;在强度上,影响黑龙江的超强台风居多,但近年趋于减少,更多低级别的热带气旋可维持较长生命史北上产生影响;牡丹江市为黑龙江最易受热带气旋影响的地区;按移动路径可将影响黑龙江的热带气旋分为两类,分别为北上热带气旋和偏东路径热带气旋,其中北上热带气旋又可进一步分为七类,其中经朝鲜半岛东转向出现的频次最多,但对黑龙江影响相对较小;经朝鲜半岛北上和高纬东转向更容易给黑龙江带来严重的风雨影响。     

Influences of Tropical Cyclones on China During 1965-2004

Using the Joint Typhoon Warning Center （JTWC） and China Meteorological Administration （CMA） tropical cyclone track datasets, variations in frequency and intensity of the affecting-China tropical cyclones （ACTCs） are studied for the period of 1965-2004. First, the differences between the two tropical cyclone datasets are examined. The annual frequencies of tropical cyclones in the western North Pacific basin are reasonably consistent to each other, while the intensity records are less reliable. The annual numbers of ACTCs based on different datasets are close to each other with similar interdecadal and interannual variations. However, the maximum intensity and the annual frequency of ACTCs for strong categories show great dependence on datasets. Tropical cyclone impacts on China show the same variations as the annual number of ACTCs and also show dependence on datasets. Differences in tropical cyclone impacts on China are mainly caused by datasets used. The annual frequency of ACTCs, especially the length of lifetime of ones that make landfall, and the intensity estimates all have effects on the value of impacts on China.     

Application of evidence theory to quantify uncertainty in hurricane/typhoon track forecasts

Summary In the paper, a new technique to quantify the accuracy of models for weather prediction in forecasting tracks of tropical cyclones using the available best track database is presented. Also a new approach to quantify and improve the accuracy of tropical cyclone track forecasts where no best track positions are available is suggested. Both techniques rely on the mathematical tools of evidence theory, which are customized here for application to total uncertainty in track forecasts.     

风云气象卫星“一带一路”热带气旋监测能力与最新进展

面向风云卫星服务“一带一路”倡议,我国风云气象卫星在轨运行的静止和极轨两个系列6颗卫星,已经联合组成了服务“一带一路”星座布局,建立了风云卫星应急减灾数据服务机制。本文对利用FY-2H、FY-4A和FY-3C/D开展的“一带一路”热带气旋监测方法以及最新进展进行了概述,列举了2018年和2019年影响力较大的连续致灾热带气旋、跨海域热带气旋,以及双/三/四个热带气旋共存的典型个例。结果显示在基于风云卫星开展的“一带一路”热带气旋监测业务中,将热带气旋发生演变的原理与气象卫星不同仪器观测原理相结合,在热带气旋生命史不同阶段根据所关注的不同侧重点,分别对应应用风云气象卫星不同观测仪器,对于热带气旋全生命史监测预报有重要意义。     

Impact of vortex-removal from environmental flow in cyclone track prediction using Lagrangian advection model

In the present study, a new approach is discussed to find out the residual steering flow from the high-resolution global Numerical Weather Prediction (NWP) model-forecasted wind fields, which have been used in the Lagrangian advection model to determine the track of tropical cyclones formed in the Indian Ocean. The Lagrangian advection model is newly developed model and conceptually closer to the dynamical models, which utilizes environmental steering flow and the effect due to earth’s rotation (the beta-effect) to determine the motion of cyclone. In this approach, the effect of environmental flow on the cyclone track is examined by removing the existing cyclone vortex from the steering flow which is determined by potential vorticity approach. A new approach based on vortex pattern matching has been used to identify the cyclone vortex and to remove it from the steering flow. The tracks of five tropical cyclones (viz., Nargis, Khai_Muk, Nisha, Aila and Phyan) which were formed in the North Indian basin during the period 2008–2009 have been generated by the Lagrangian advection model using the proposed scheme. The position errors were computed with respect to the Joint Typhoon Warning Center (JTWC) best track analysis positions and compared with that of without-vortex-removal scheme. The results show that the mean track errors for five cyclones are reduced by 6–35?% for 12–72?h forecast in case of vortex-removal scheme as compared to the without-vortex-removal scheme.     

Estimates of tropical cyclone effects on the upper layer in the seas of Japan and Okhotsk

On the basis of climate and reanalysis data, a contribution is estimated of tropical cyclones (TCs) to the fluxes of heat, moisture, momentum, and mechanical energy of wind over the seas of Japan and Okhotsk. The estimates are obtained for two TCs that passed over these areas. It is shown that when TCs move over both seas, the heat and moisture exchange between the sea surface and the atmosphere increases approximately by a factor of 3. Also, a significant dynamic effect of tropical cyclones on the upper ocean layer is noted, so that the flux of mechanical wind energy exceeds the background monthly mean values by a factor of 10 or more. On the example for the Far East seas, a well-pronounced dependence of disturbances in the upper ocean on intensity, size, and dynamics of the cyclone is shown.     

基于春季气候信号的“台风是否经过江苏”预测研究

利用中国气象局提供的1951—2018年台风最佳路径数据集,筛选经过江苏的热带气旋个例,发现历史上所有经过江苏的热带气旋都发生在夏秋季节。基于春季130种气候信号指数,利用C4.5决策树算法建立“台风是否经过江苏”的预测模型。结果表明:基于C4.5算法的决策树能够较为直观且准确地对每年“台风是否经过江苏”进行预测。利用1951—2000年(51 a)的数据样本进行训练,学习准确率达到82%,利用2001—2018年(18 a)的数据样本对模型进行泛化能力测试,测试准确率达到83.3%,最后利用2019年第9号热带气旋“利奇马”经过江苏的事实进行个例检验,符合决策树规则C。可以证明C4.5算法对“台风是否经过江苏”的预测具有较高的准确率和通用性。     

Statistical and Comparative Analysis of Tropical Cyclone Activity over the Arabian Sea and Bay of Bengal (1977–2018)

A statistical comparative analysis of tropical cyclone activity over the Arabian Sea and Bay of Bengal (BoB) has been conducted using best-track data and wind radii information from 1977 to 2018 issued by the Joint Typhoon Warning Center. Results have shown that the annual variation in the frequency and duration of tropical cyclones has a significant increasing trend over the Arabian Sea and an insignificant decreasing trend over the BoB. The monthly frequency of tropical cyclones in both the Arabian Sea and the BoB shows a notable bimodal character, with peaks occurring in May and October–November, respectively. The maximum frequency of tropical cyclones occurs in the second peak as a result of the higher moisture content at mid-levels in the autumn. However, the largest proportion of strong cyclones (H1–H5 grades) occurs in the first peak as a result of the higher sea surface temperatures in early summer. Tropical cyclones in the Arabian Sea break out later during the first peak and activity ends earlier during the second peak, in contrast with those in the over BoB. This is related to the onset and drawback times of the southwest monsoon in the two basins. Tropical cyclones in the Arabian Sea are mainly generated in the eastern basin, whereas in the BoB the genesis locations have a meridional (zonal) distribution in May–June (October–November) as a result of the seasonal movement of the low-level positive vorticity belt. The Arabian Sea is dominated by western and northwestern tropical cyclones by that track west and NW, accounting for about 74.6%, whereas the tropical cyclones with a NE track account for only 25.4%. The proportions of the three types of tracks are similar in the BoB, with each accounting for about 33% of the tropical cyclones. The mean intensity and size of tropical cyclones over the Arabian Sea are stronger and larger, respectively, than those over the BoB and the size of tropical cyclones over the North Indian Ocean in early summer is larger than that in autumn. The asymmetrical structure of tropical cyclones over North Indian Ocean is affected by the topography and the longest radius of the 34 kt surface wind often lies in the eastern quadrant of the tropical cyclone circulation in both sea areas. FAN Xiao-ting (樊晓婷), LI Ying (李 英), et al.