热带气旋Meranti(2010)异常路径的成因分析

采用MTSAT2卫星红外云图资料及NCEP/NCAR再分析资料,研究了热带气旋Meranti(2010)异常路径的成因。结果表明:Meranti的路径由西行、打转、北上三个阶段组成。在西行、北上阶段,环境场引导流起着主要作用,Meranti的非对称结构对其也有一定影响,非对称对流系统的作用较弱。在打转阶段,环境场引导流和非对称结构均不能解释Meranti打转的原因,而非对称对流系统则起着主要作用。不同阶段的Meranti外缘线的分形维数特征存在明显区别。在西行、北上阶段,其分形维数处于高值段且变化平缓;在打转阶段,则处于低值段且变化较大。     

多光谱卫星图像的一种模糊聚类方法

基于二维光谱特征空间，用模糊C均值(FCM)聚类方法，对多光谱静止卫星(GMS-5)图像进行了云分类试验，得到了比较合理的分类结果。该方法利用不同光谱通道的卫星云图光谱特征构造出一个二维光谱特征空问，对云图在特征空间上的光谱特征点进行FCM聚类，然后与已知云类样本的特征进行比较，确定出各聚类域的类属，进而得到二维光谱空间的云分类图，实况接收的云图可通过查验特征像素点在分类图中的落区位置来实现云的分类。     

近60年永兴岛热带气旋降水的气候特征分析

对1958—2019年期间,进入永兴岛及附近区域(11.5°～21.5°N,101.2°～117.5°E)范围内的热带气旋(Tropical Cyclone,TC)的气候特征进行分析,结果表明:(1)永兴岛平均每年受9.4个TC影响,TC有显著的下降趋势,以0.68个/10a逐渐减少,趋势系数为-0.406;(2)永兴岛TC路径分为5类:向西直行偏北类(A类)、向西直行偏南类(B类)、转向东北类(C类)、转向西南类(D类)、从西向东北类(E类),其中A类占比最大,占52.0%;(3)TC年均降水有显著的下降趋势,其回归系数为-61.76mm/10a,趋势系数为-0.270;(4)TC活动对永兴岛强降雨贡献最多,达到67.8%,其他天气系统对永兴岛强降雨的贡献仅为32.2%,年均TC强降雨日数为4.1d,非TC强降雨日数为2.8d,TC强降雨对总强降雨的贡献率无明显的趋势变化,其回归系数为0.57/10a,趋势系数为0.055,而TC强降雨日数的贡献率则呈现下降趋势,其回归系数为-4.7/10a,趋势系数为-0.335,通过α=0.01显著性检验。     

双光谱云图的云分类探讨

依据各类云在红外和可见光波段不同的光谱特性，考察了近百个数字云图样本，在红外－可见光二维光谱特征空间上基本确定了与种类相应的集群分布范围，由此判识出积雨云、薄卷云、厚卷云、中云、低云、沈积云和多层云系等７种主要云类及晴空区。并以１９９０年３月１５日１４时云图为例进一步讨论了诸云类在光谱特征空间上高频数分布区的形状和分布特点。     

多阈值和神经网络卫星云图云系自动分割试验

卫星云图自动分割是实现卫星云图云系自动识别的基础.选用1992~1994年和1997~1998年夏季有典型天气系统的177幅GMS红外云图建立了云系模型库, 云系分类样本3079个, 包含16类云系, 云系分割样本2764个.利用云系分割样本集进行神经网络试验, 训练集为从32幅云图中抽取的484个样本, 测试集为从145幅云图中抽取的2280个样本, 神经网络模型训练正确率达到98.8%, 测试正确率为86.4%.用1997年7月18~21日和1998年6月15~17日的两组卫星云图做自动分割应用试验, 结果经专家判识, 正确率达到90%以上.本文的工作表明:用多阈值和人工神经网络相结合方法对卫星云图进行云分割在实际应用中是可行的. 卫星云图自动分割系统的输入是GMS红外云图, 输出是分割出的每一个云区, 同时还包括云区的边界链码、起始点、周长、面积, 并保留了原始图像数据.在下一步的云系识别过程中, 可以在此基础上进行云系分类识别试验.     

基于可见光——红外图像信息融合的云状识别方法

云状的正确观测对降水测报具有指示性意义,云状自动识别技术是气象要素自动化观测领域的难题之一。本文基于全天空可见光成像仪采集的云图与中红外热像仪获取的云图结合,对天空云状进行分类和测量。结果表明:通过在北京、杭州和丽江气象台站采集的大量云图,从云图特征和降水指示性方面将云状划分为Clear、C_H、C_L、C_B及C_M共5类。选取14个色彩和纹理特征值作为云状计算参数,采用552张云图作为训练样本,信息分类利用特征值加权最小距离算法,对于5类500个被测样本进行云状的判别。对应自拟的标准云状分类,平均准确率为82%。基于可见光—红外图像信息融合的云状识别方法结合了可见光图像色彩信息丰富的特点及红外图像可以降低雾霾干扰的优势,对比单一可见光传感器云测量,准确性有所提高。本文在可见光与红外图像传感器等多种云观测设备的信息融合方面进行了有益的尝试。     

风云二号静止气象卫星的作用和效益

20 0 0年 6月 2 5日晚 7时 5 0分 ,我国的风云二号第二颗静止气象卫星在西昌卫星发射中心发射升空 ,并于 7月 3日晚 2 1点 2 9分成功地定点于 1 0 5°E的赤道上空。 7月 6日 1 3时 0 8分星上的扫描辐射仪开机 ,获取了此星的第一幅可见光云图。图像清晰 ,云型特征明显 ,标志着该星的各个环节均正常工作。经过在轨测试之后 ,7月 2 0日红外通道开机 ,得到清晰的红外和水汽云图。经过进一步在轨测试和调整之后 ,风云二号第二颗星将逐渐进入业务试运行和业务运行状态。我国和周边地区的气象部门和气象卫星资料应用单位将通过 92 1 0和中规模利用…     

GMS—5卫星图象产品简介

省气象信息网络中心自1995年8月份起处理、上网GMS—5卫星云图,给各网络用户提供三个通道、二种投影共五类云图图象产品,即红外兰勃脱图、红外麦考托图、可见光麦考托图、水汽兰勃脱图和未投影的可见光图.本文介绍了卫星图象产品的特点、接收情况及各种云图的观测原理,供大家参考.1 新卫星与GMS—4卫星的不同点及接收简况GMS—5卫星是1995年3月份日本发射的静止卫星,它与GMS—4相比作了一些改进,将GMS—4的红外探测通道波段10.5～12.5μm分割为两个通道,红外1:10.5～11.5μm,红外2:11.5～12.5μm并增加了红外3为水汽通道,波段为6.5～7.0μm,可见光波段从0.55～0.75μm改为0.55～0.90μm.     

FY2-C静止气象卫星资料处理方法

随着空间技术和遥感技术的迅速发展,静止气象卫星资料以其覆盖范围广、时间分辨率高等优势,被广泛应用于天气预报、环境监测、防灾减灾等领域[1-2]。中国第一颗业务静止气象卫星风云二号C星(FY2-C)于2004年10月19日发射升空,2005年1月1日起,FY2-C开始试验广播展宽云图,为用户提供服务,在2005年汛期前全面投入业务运行。FY2-C定位于地球赤道上空约35800km的地球同步轨道上,星下点中心位置为0°N,105°E,星上扫描辐射计有5个通道,其播发的延时可见光和红外自旋扫描辐射计(S-VISSR)展宽数据包括白天可见光云图、昼夜红外云图和水汽云图…     

涡旋边缘线的分形特征

非线性作用可以使初始时刻等值线光滑的圆形和椭圆形涡旋演化为边缘不光滑、面积大小不等的多个涡旋和涡块共存的复杂流型。这些涡旋和涡块的边缘线具有分形特征,其数值与Ｌｏｖｅｊｏｙ根据卫星云图和雷达探测资料求得的热带云块边缘线的分形结果较为接近     

A modeling study on the effects of MJO and equatorial Rossby waves on tropical cyclone genesis over the western North Pacific in June 2004

This study investigates the influence of the Madden Julian oscillations (MJO) and equatorial Rossby (ER) waves on tropical cyclone (TC) formation in western Pacific during June 2004 through one control and three wave experiments for each of the five TCs. The control experiment reasonably simulates the formation of five TCs. In the corresponding wave experiments, the MJO, ER waves, and both the MJO and ER waves are removed, from the initial fields and lateral boundary conditions, respectively. The differences of simulated TC intensity between the control and corresponding wave experiments provide a quantitative assessment of the relative contribution of each wave to TC formation.In the wave experiments with the MJO removed, three of the five TCs are weakened, and the remaining two (TC A and B) grow stronger due to an altered background flow that steered the TCs into more favorable oceanic regions. For the wave experiments with ER waves removed, three of the five simulated TCs become weaker (TC A, C, and E). TC D develops into a tropical storm because of a dominant influence from active synoptic-scale disturbance. The results indicate that both the MJO and ER waves have an important modulating effect on TC formation. In addition to the influence from the MJO, ER and synoptic-scale waves, local processes may dominate in TC formation; for the example of TC B, none of the waves positively influence the formation in significant ways. The present modeling approach provides a quantitative assessment of the relative contribution of tropical wave disturbances to TC formation.     

西北太平洋热带气旋快速增强阶段的风速分布特征

利用联合台风预警中心的最优路径（best-track）资料,筛选出西北太平洋地区快速增强和非快速增强两类热带气旋样本。利用美国国家海洋与大气管理局（NOAA）的多平台热带气旋表面风分析资料,对比分析了两类样本的风速和涡度的分布特征。结果显示,快速增强的热带气旋样本通常结构更紧凑,最大风速较大,最大风速半径较小,台风内区的风速较大。在涡度上表现为快速增强热带气旋样本内区的涡度和涡度梯度较大。对两类样本进行t检验,结果显示两类样本内区的切向风差异明显,说明热带气旋的内区风速分布与其发展之间存在密切联系。其物理机制可能是:当存在较大的内区涡度梯度时,涡度隔离机制有利于对流单体向涡旋中心汇聚,此外较大的涡度意味着较大的惯性稳定度,有利于非绝热加热向热带气旋动能的转换,二者共同作用有利于热带气旋的快速发展。      

西北太平洋热带气旋强度变化的若干特征

使用NOAA海表温度资料、ECMWF再分析资料和JTWC台风最佳路径数据,对1984—2013年30年西北太平洋热带区域（100 °E~180 °,0~60 °N）内热带气旋（TC）的强度变化特征及其与环境风垂直切变（VWS）、海表温度（SST）、最大风速半径（RMW）的关系作了统计分析,尤其关注TC强度突变。结果表明:（1）在研究区域内,TC样本中35.2%强度稳定,52.8%强度变化缓慢,仅12.0%强度突变,约92.7%的迅速加强TC样本发生在其台风及以上强度等级;（2）2000年以来,TC强度稳定样本减少,强度迅速变化样本增多。5月和9—10月是TC强度突变的高频期;（3）超过12 m/s的环境VWS下TC迅速加强较少,且只有台风及以上强度TC才能在大于12 m/s的VWS下迅速加强;（4）TC加强和迅速加强主要在28.5~30.0 ℃的SST洋面上发生,在较低SST下仍迅速加强的TC强度等级较高;（5）TC样本的RMW多小于100 km,其中强度突变TC RMW峰值区在20~40 km;（6）加强TC的RMW的24 h变化一般减小,减弱TC的RMW则增大;其中强度突变TC尤其明显,超强台风发生迅速加强时,RMW减小的比率达84.6%,但仍有15.4%比率的RMW增大。      

2018年西北太平洋台风活动特征和预报难点分析

利用1949—2018年中国气象局台风最佳路径、2018年中央气象台的台风路径强度实时预报、ECMWF数值预报以及NCEP逐日高分辨率海温RTG_SST(0.083°×0.083°)等资料,对2018年西北太平洋台风活动的主要特征和预报难点进行了分析。结果表明:2018年台风生成频数偏多,生成源地偏东,南海台风活跃;生成时间集中,盛夏台风异常偏多,台风群发性强,双台风或多台风共存活动频次偏多;台风生命史长,累积气旋能量偏高,超强台风偏多,但整体强度偏弱,较弱台风异常偏多;台风登陆频数和频次偏多,登陆地段偏北,且登陆台风强度明显偏弱。中央气象台24~120 h台风路径预报误差分别为72、124、179、262和388 km,各时效误差较2017年均有减少,特别是长时效路径预报误差明显减少;24~120 h台风强度预报误差分别为3.7、5.1、5.5、6.6和7.1 m·s^-1。由于双台风或多台风之间的相互作用、“鞍型场”等造成路径预报难度大以及多台风之间复杂水汽输送、近海台风强度变化不确定性大等原因,造成强度预报难度大。若采用更多观测资料、进行更深入的台风机理研究以及研发更有效的台风客观预报技术将是突破这些难点的有效途径。     

Reexamination of the Relationship between Tropical Cyclone Size and Intensity over the Western North Pacific

This study reexamines the correlation between the size and intensity of tropical cyclones (TCs) over the western North Pacific from the perspective of individual TCs, rather than the previous large-sample framework mixing up all TC records. Statistics show that the positive size-intensity correlation based on individual TCs is relatively high. However, this correlation is obscured by mixing large samples. The weakened correlation based on all TC records is primarily due to the diversity in the size change relative to the same intensity change among TCs, which can be quantitatively measured by the linear regression coefficient (RC) of size against intensity. To further explore the factors that cause the variability in RCs that weakens the size-intensity correlation when considering all TC records, the TCs from 2001 to 2020 are classified into two groups according to their RC magnitudes, within which the high-RC TCs have a larger size expansion than the low-RC TCs given the same intensity change. Two key mechanisms responsible for the RC differences are proposed. First, the high-RC TCs are generally located at higher latitudes than the low-RC TCs, resulting in higher planetary vorticity and thus higher planetary angular momentum import at low levels. Second, the high-RC TCs are susceptible to stronger environmental vertical wind shear, leading to more prolific outer convection than the low-RC TCs. The positive feedback between outer diabatic heating and boundary layer inflow favors the inward import of absolute angular momentum in the outer region, thereby contributing to a larger size expansion in the high-RC TCs.     

Thermodynamic Characteristics of Tropical Cyclones with RapidIntensity Change over the Coastal Waters of China

In order to investigate the different thermodynamic mechanisms between rapid intensifying (RI) and rapid weakening (RW) tropical cyclones (TCs),the thermodynamic structures of two sets of composite TCs are analyzed based on the complete-form vertical vorticity tendency equation and the NCEP/NCAR reanalysis data.Each composite is composed of five TCs,whose intensities change rapidly over the coastal waters of China.The results show that the maximum apparent heating source Q1 exists in both the upper and lower troposphere near the RI TC center,and Q1 gets stronger at the lower level during the TC intensification period.But for the RW TC,the maximum Q1 exists at the middle level near the TC center,and Q1 gets weaker while the TC weakens.The maximum apparent moisture sink Q2 lies in the mid troposphere.Q2 becomes stronger and its peak-value height rises while TC intensifies,and vice versa.The increase of diabatic heating with height near the TC center in the mid-upper troposphere and the increase of vertical inhomogeneous heating near the TC center in the lower troposphere are both favorable to the TCs' rapid intensification; otherwise,the intensity of the TC decreases rapidly.     

Experiments of DSAEF_LTP Model with Two Improved Parameters for Accumulated Precipitation of Landfalling Tropical Cyclones over Southeast China

The Dynamical-Statistical-Analog Ensemble Forecast model for landfalling tropical cyclones (TCs) precipitation (DSAEF_LTP) utilises an operational numerical weather prediction (NWP) model for the forecast track, while the precipitation forecast is obtained by finding analog cyclones, and making a precipitation forecast from an ensemble of the analogs. This study addresses TCs that occurred from 2004 to 2019 in Southeast China with 47 TCs as training samples and 18 TCs for independent forecast experiments. Experiments use four model versions. The control experiment DSAEF_LTP_1 includes three factors including TC track, landfall season, and TC intensity to determine analogs. Versions DSAEF_LTP_2, DSAEF_LTP_3, and DSAEF_LTP_4 respectively integrate improved similarity region, improved ensemble method, and improvements in both parameters. Results show that the DSAEF_LTP model with new values of similarity region and ensemble method (DSAEF_LTP_4) performs best in the simulation experiment, while the DSAEF_LTP model with new values only of ensemble method (DSAEF_LTP_3) performs best in the forecast experiment. The reason for the difference between simulation (training sample) and forecast (independent sample) may be that the proportion of TC with typical tracks (southeast to northwest movement or landfall over Southeast China) has changed significantly between samples. Forecast performance is compared with that of three global dynamical models (ECMWF, GRAPES, and GFS) and a regional dynamical model (SMS-WARMS). The DSAEF_LTP model performs better than the dynamical models and tends to produce more false alarms in accumulated forecast precipitation above 250 mm and 100 mm. Compared with TCs without heavy precipitation or typical tracks, TCs with these characteristics are better forecasted by the DSAEF_LTP model.     

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。     

Autumn Tropical Cyclones over the Western North Pacific during 1949-2016: A Statistical Study

We used tropical cyclone (TC) best track data for 1949–2016, provided by the Shanghai Typhoon Institute, China Meteorological Administration (CMA-STI), and a TC size dataset (1980-2016) derived from geostationary satellite infrared images to analyze the statistical characteristics of autumn TCs over the western North Pacific (WNP). We investigated TC genesis frequency, location, track density, intensity, outer size, and landfalling features, as well as their temporal and spatial evolution characteristics. On average, the number of autumn TCs accounted for 42.1% of the annual total, slightly less than that of summer TCs (42.7%). However, TCs classified as strong typhoons or super typhoons were more frequent in autumn than in summer. In most years of the 68-yr study period, there was an inverse relationship between the number of autumn TCs and that of summer TCs. The genesis of autumn TCs was concentrated at three centers over the WNP: the first is located near (14°N, 115°E) over the northeastern South China Sea and the other two are located in the vast oceanic area east of the Philippines around (14°N, 135°E) and (14°N, 145°E), respectively. In terms of intensity, the eight strongest TCs during the study period all occurred in autumn. It is revealed that autumn TCs were featured with strong typhoons and super typhoons, with the latter accounting for 28.1% of the total number of autumn TCs. Statistically, the average 34-knot radius (R34) of autumn TCs increased with TC intensity. From 1949 to 2016, 164 autumn TCs made landfall in China, with an average annual number of 2.4. Autumn TCs were most likely to make landfall in Guangdong Province, followed by Hainan Province and Taiwan Island.

     

STATISTICAL AND COMPOSITE ANALYSIS OF RELATIONSHIP BETWEEN THE NUMBER OF CONVECTIVE CORES AND THE CHARACTERISTICS OF TBB WITHIN THE TROPICAL CYCLONE CIRCULATION AND ITS INTENSITY

Based on the data(including radius of maximum winds) from the JTWC(Joint Typhoon Warning Center),the tropical cyclones(TCs) radii of the outermost closed isobar, TCs best tracks from Shanghai Typhoon Institute and the Black Body Temperature(TBB) of the Japanese geostationary meteorological satellite M1 TR IR1, and combining13 tropical cyclones which landed in China again after visiting the island of Taiwan during the period from 2001 to2010, we analyzed the relationship between the number of convective cores within TC circulation and the intensity of TC with the method of convective-stratiform technique(CST) and statistical and composite analysis. The results are shown as follows:(1) The number of convective cores in the entire TC circulation is well corresponding with the outer spiral rainbands and the density of convective cores in the inner core area increases(decreases) generally with increasing(decreasing) TC intensity. At the same time, the number of convective cores within the outer spiral rainbands is more than that within the inner core and does not change much with the TC intensity. However, the density of convective cores within the outer spiral rainbands is lower than that within the inner core.(2) The relationship described above is sensitive to landing location to some extent but not sensitive to the structure of TC.(3) The average value of TBB in the inner core area increases(decreases) generally with increasing(decreasing) of TC intensity, which is also sensitive to landing situation to some extent. At the same time, the average value of TBB within the outer spiral rainbands is close to that within the entire TC circulation, and both of them are more than that within the inner core. However, they do not reflect TC intensity change significantly.(4) The results of statistical composite based on convective cores and TBB are complementary with each other, so a combination of both can reflect the relationship between TC rainbands and TC intensity much better.