近百年西北太平洋热带气旋年频数的变化特征

利用经趋势订正的１８８４－１９８８年西北太平洋热带气旋年频数资料，分析了热带气旋年频数的多年变化及其与海面温度、南方涛动指数、太阳黑子数和环流型日数等的统计关系。初步结果表明，热带气旋年频数的变化具有明显的２１年、３１年、１５年和６年左右的周期和持续期平均为１２年左右的阶段变化；近百年来有三次较明显的转折，分别出现在１９３１、１９５９年１９７７年。热带气旋年频数在厄尔尼诺年有冬春季偏少、夏秋季偏多     

影响广西的热带气旋年频数的BP神经网络预测模型

对影响广西的热带气旋(TC)年频数与大气环流的关系进行分析表明,TC年频数与全球范围大气环流异常有密切关系,特别是春季南半球中高纬度环流异常和低纬越赤道气流异常.利用相关分析从春季全球大气环流场中选择初选预报因子,然后对初选预报因子作EOF展开构造综合预报因子,运用BP神经网络方法建立TC年频数预报模型,并对所建立的模型进行独立样本试验.结果表明,该预报模型对历史样本拟合精度高,试报效果优于传统的逐步回归模型,可在汛期预测业务中应用.     

西北太平洋热带气旋的年际和年代际变化及其与南亚高压的关系

利用1949～1996年48年西北太平洋热带气旋(TC)的年个数资料和1958～1997年40年南亚高压(SAH)特征参数的月平均资料，讨论了西北太平洋TC年个数的年际、年代际变化、年个数周期和周期能量等特点及其与SAH特征参数的关系和异常TC年前期SAH环流场和100 hPa高度场的特征。结果表明，西北太平洋TC具有明显的年际和年代际变化，前期SAH对当年TC频数有一定影响，SAH中心位置偏北、偏西，中心强度偏弱时，当年TC偏多，反之，当年TC偏少。     

IMPACT OF LARGE-SCALE CIRCULATION ON THE INTERDECADAL VARIATIONS OF THE WESTERN NORTH PACIFIC TROPICAL CYCLONE

Based on the annual frequency data of tropical cyclones from 1960 to 2005 and by the polynomial fit and statistical analysis, this work has discovered that TC activity in the 46a exhibits significant decadal- scale variability. It has two high frequency periods (HFP) and two low frequency periods (LFP). Significant differences in the number of TCs between HFP and LFP are found in active TC seasons from July to October. Differences of large-scale circulation during HFP and LFP have been investigated with NCEP/NOAA data for the season. In HFP, the condition includes not only higher sea surface temperature,lower sea level pressure, larger divergence of upper air, larger relative vorticity at low levels and smaller vertical shear, but also 500-hPa wind vector being more available for TC activity and moving to western North Pacific, the position of the subtropical anticyclone over the western Pacific shifting more northward,and South Asian Anticyclone at 100-hPa being much smaller than that in LFP. The precipitation of western North Pacific has no clear influence on TC activity.     

百余年来影响福建热带气旋的变化特征

应用1884—2003年影响福建的热带气旋资料, 采用突变分析、最大熵谱分析、连续小波变换以及正交小波变换等方法研究百余年来影响福建热带气旋频数变化的多时间尺度特征及其异常年份的海气背景场特征。结果表明:百余年来福建经历了3次少台期和2次多台期, 影响福建热带气旋频数具有准13年、准4年和准2.5年的振荡周期, 1971年为年频数变化的突变点; 影响福建热带气旋频数近百年呈弱的上升趋势, 但近十几年略微下降, 未来有偏多的趋势; 影响福建热带气旋异常偏多 (少) 的年份, 夏季500 hPa高度场上, 鄂霍次克海地区位势高度偏低 (高), 从高纬到低纬呈“-+-”(“ +-+”) 的距平型, 纬 (经) 向环流占优势, 西风带低槽偏北 (南), 副热带高压北界偏北 (南), 副热带高压脊线偏北 (南); 赤道中、东太平洋为明显的带状负 (正) SSTA距平区, 同时西太平洋热带气旋主要源区和西北太平洋上皆为正 (负) SSTA距平。由此可见, 影响福建热带气旋频数多寡与西太平洋热带气旋生成区的海温有关, 同时大气环流系统的位置和强弱对热带气旋路径的变化起着关键性作用, 从而使影响福建热带气旋频数的变化。     

THE ABRUPT CHANGE OF TROPICAL CYCLONE NUMBER OVER THE WESTERN NORTH PACIFIC IN THE MID-1990s

Based on the CMA tropical cyclone(TC) best track data as well as the reanalysis datasets from the NCEP/NCAR and NOAA, the variation characteristics of TC number from 1949 to 2013 over the western North Pacific(including the South China Sea) are examined. Notably, the time series of TC number exhibits a significant abrupt change from more to less around 1995. Comparative analysis indicates that the environmental factors necessary to TC formation also change significantly around the mid-1990 s. After 1995, accompanying with anomalous warm sea surface temperature(SST) in western equatorial Pacific, a La Nia-like pattern in tropical Pacific appears obviously. However,compared with the period before 1995, the vertical upward movement decreases, vertical shear of tropospheric zonal wind increases, and sea level pressure(SLP) rises, all of which are unfavorable to TC formation and work together to make TC number reduce markedly after 1995. Furthermore, when the typical interannual more and less TCs years are selected in the two separate stages before and after 1995, the relative importance of oceanic and atmospheric environments in interannual TC generation is also investigated respectively. The results imply that the SST over the tropical Pacific exerts relatively important influence on TC formation before 1995 whereas the atmospheric circulation plays a more prominent role in the generation of TC after 1995.     

CWRF对中国近海热带气旋活动季节和年际变化及环境场影响的模拟

利用欧洲中期天气预报中心的ERA-Interim再分析资料驱动CWRF模式对1982-2016年中国近海的热带气旋活动进行了模拟,分析了CWRF对热带气旋频数季节、年际变化和路径的模拟能力,并探讨了环境场模拟对热带气旋模拟的影响。结果表明:CWRF能够合理模拟热带气旋频数的季节和年际变化,但模拟的频数较观测总体偏低,季节变化模拟总体优于年际变化的模拟;模式基本上能模拟出热带气旋路径密度的空间分布,但CWRF明显总体低估了气旋路径密度。进一步分析发现,模式模拟的环境场对模拟结果具有十分重要的影响。850 hPa气旋性与反气旋性环流异常对热带气旋频数影响显著;200 hPa反气旋性环流异常与东亚西风急流对热带气旋路径影响较大;副高会影响洋面对流运动从而影响热带气旋频数,其南侧偏东风则会影响热带气旋路径;垂直风切变偏小,在不同纬度对热带气旋的影响是不同的。     

SIMULATION OF TROPICAL CYCLONES OVER THE WESTERN NORTH PACIFIC AND LANDFALLING IN CHINA BY REGCM4

This study evaluates the performance of the regional climate model RegCM4 in simulating tropical cyclone (TC) activities over the Western North Pacific (WNP) and their landfalling in China. The model is driven by ERA-Interim boundary conditions at a grid spacing of 25 km, with the simulation period as 1991–2010. Results show that RegCM4 performs well in capturing the main structural features of observed TCs, and in simulating the genesis number and annual cycle of the genesis. The model reproduces the general pattern of the observed TC tracks and occurrence frequency. However, significant underestimation of the occurrence frequency as well as the TC intensity is found. Number of the landfalling TCs over China is also much less than the observed. Bias of the model in reproducing the large-scale circulation pattern and steering flow may contribute to the underestimated landfalling TC numbers.     

K-MEANS CLUSTERING FOR CLASSIFICATION OF THE NORTHWESTERN PACIFIC TROPICAL CYCLONE TRACKS

Based on the Joint Typhoon Warning Center (JTWC) best-track dataset between 1965 and 2009 and the characteristic parameters including tropical cyclone (TC) position, intensity, path length and direction, a method for objective classification of the Northwestern Pacific tropical cyclone tracks is established by using K-means Clustering. The TC lifespan, energy, active season and landfall probability of seven clusters of tropical cyclone tracks are comparatively analyzed. The characteristics of these parameters are quite different among different tropical cyclone track clusters. From the trend of the past two decades, the frequency of the western recurving cluster (accounting for 21.3% of the total) increased, and the lifespan elongated slightly, which differs from the other clusters. The annual variation of the Power Dissipation Index (PDI) of most clusters mainly depended on the TC intensity and frequency. However, the annual variation of the PDI in the northwestern moving then recurving cluster and the pelagic west-northwest moving cluster mainly depended on the frequency.     

东亚高层纬向风季节内振荡与盛夏登陆中国大陆热带气旋频数年际变化的联系

利用1979—2017年欧洲中期天气预报中心提供的ERA-Interim再分析数据与中国气象局-上海台风研究所(China Meteorological Administration-Shanghai Typhoon Research Institute,CM A-STI)、美国联合台风警报中心(Joint Typhoon Warning Center,JTWC)整编的西北太平洋热带气旋(Tropical Cyclone,TC)资料集,分析东亚高层(200hPa)纬向风季节内振荡(Intraseasonal Oscillation,ISO)与7—8月登陆中国大陆TC频数年际变化的联系。结果表明:7—8月中国大陆登陆TC频数与西风急流出口区南侧(北侧)纬向风为显著负(正)相关,南侧显著相关区与北侧的差定义的东亚西风急流指数(East Asian Westerly Jet Index,EAWJI)可定量描述急流经向移动,EAWJI负异常时急流北移、登陆TC偏多,反之急流南移、登陆TC偏少。急流北移,TC活动区域对流层高层呈偏东风异常,产生异常东风切变,有利于TC登陆过程的维持,使登陆中国大陆TC频数增多。东亚高层纬向风ISO与年际变化的标准差场、EOF模态的高度相似性说明两者由同一空间主导模态所控制,表明若其ISO偏北偏南振荡发生频率为非正态分布,剩余偏差将改变其季节平均。TC登陆多年,东亚西风急流指数ISO呈更高频率偏北移动,引起急流出口区南侧ISO尺度扰动涡度通量辐合,使季节平均西风减小,急流位置北移,说明高层纬向风ISO可通过间接调制影响TC登陆的大尺度环流进而与登陆TC频数的年际变化相联系。     

1891—1990年期间北半球大气环流和中国气候的变化

根据1891–1990年北半球大气环流型W、C、E年频数以及全国平均年温、北京和上海的年温的时间序列，计算分析了它们各自的主值函数、功率谱和凝聚谱，得到了环流和温度的百年长期趋势、周期谱图和它们之间的凝聚关系，并用距平累加曲线法，相邻两阶段的信噪比法，揭示了环流和温度在近百年变化过程中的转折和突变。最后，用Mann-Kendall法对它们作了检验。讨论了环流异常与气候异常的关联性，并给予一定的解释。     

冬季北半球大气低频环流型的年际变化特征

采用NCEP/NCAR逐日再分析资料,利用31点数字滤波器提取了58个冬季(1951/1952-2008/2009年)的500 hPa高度场低频分量,通过经验正交函数分析方法定义了6种低频环流型.从逐年低频环流型的差异和低频环流型系数两个角度分析低频环流型的年际变化特征;给出了58个冬季的主要低频环流型并分析了逐年低频...     

ENSO and Western North Pacific tropical cyclone activity simulated in a CGCM

A high-resolution (T213) coupled ocean–atmosphere general circulation model (CGCM) has been used to examine the relationship between El Niño/Southern Oscillation (ENSO) and tropical cyclone (TC) activity over the western North Pacific (WNP). The model simulates ENSO-like events similar to those observed, though the amplitude of the simulated Niño34 sea surface temperature (SST) anomaly is twice as large as observed. In El Niño (La Niña) years, the annual number of model TCs in the southeast quadrant of the WNP increases (decreases), while it decreases (increases) in the northwest quadrant. In spite of the significant difference in the mean genesis location of model TCs between El Niño and La Niña years, however, there is no significant simultaneous correlation between the annual number of model TCs over the entire WNP and model Niño34 SST anomalies. The annual number of model TCs, however, tends to decrease in the years following El Niño, relating to the development of anticyclonic circulation around the Philippine Sea in response to the SST anomalies in the central and eastern equatorial Pacific. Furthermore, it seems that the number of model TCs tends to increase in the years before El Niño. It is also shown that the number of TCs moving into the East Asia is fewer in October of El Niño years than La Niña years, related to the anomalous southward shift of mid-latitude westerlies, though no impact of ENSO on TC tracks is found in other months. It is found that model TCs have longer lifetimes due to the southeastward shift of mean TC genesis location in El Niño years than in La Niña years. As the result of longer fetch of TCs over warm SST, model TCs appear to be more intense in El Niño years. These relationships between ENSO and TC activity in the WNP are in good agreement with observational evidence, suggesting that a finer-resolution CGCM may become a powerful tool for understanding interannual variability of TC activity.     

SENSITIVITY FACTORS FOR TYPHOON GENESIS OVER THE WESTERN NORTH PACIFIC DURING JULY-SEPTEMBER

The paper compares the correlations between individual factors of the cyclogenesis and the number of TCs formed in the western North Pacific in July to September(NTWNP). It also compares the characteristics of zonal anomaly distribution of the factors in the primary TC source areas of the Northern Hemisphere. Results show that the vorticity factor has the closest correlation with NTWNP. In TC genesis conditions, this feature is relatively rich but not enough, which determines that it is the sensitivity factor of NTWNP's annual variation. The paper also analyzes the source of annual variation of the vorticity factor in the key area of the western North Pacific as well as its advantage in showing NTWNP. Results show that the annual variation of the vorticity factor mentioned above is related to the annual variation of Southern Oscillation, Antarctica Oscillation and the geopotential height field of East Australia, which reflects the effect of two large-scale systems in the Southern Hemisphere and ENSO(El Ni?o–Southern Oscillation) on NTWNP. Since the area where the vorticity factor is significantly correlated with NTWNP is consistent with the area of dense TC genesis sources, the vorticity factor has an obvious advantage in showing annual variation of TCs. Those features are very significant for research on the influencing mechanism of NTWNP and simulation of climate models.     

CFSv2模式产品在汛期海南热带气旋频数预测模型中的应用

利用1982—2014年汛期影响海南的热带气旋频数、NCEP/NCAR逐月再分析资料和CFSv2模式历史回报数据,分析了热带气旋频数特征及同期环流特征,并利用逐步回归构建基于模式有效预测信息的热带气旋频数预测模型。结果表明:汛期影响海南热带气旋频数的异常与同期大尺度环流变化密切相关,且CFSv2模式对其环流影响关键区具有较好的预测技巧,包括南海到热带太平洋的海平面气压、500 h Pa位势高度场、低层风及热带太平洋纬向风切变。据此,利用逐步回归构建热带气旋频数预测模型,其26 a交叉检验中实况与预测相关为0.88,距平同号率达88%;6 a预测试验仅2 a预测与观测反号,可见模型具有良好的稳定性和预测技巧,可为汛期热带气旋频数预测提供依据。     

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。     

江淮梅雨与梅雨期西北太平洋热带气旋的关系

基于梅雨综合指数,本文对1955—2010年江淮梅雨与梅雨期西北太平洋TC的变化关系及成因进行统计分析研究。结果表明:梅雨强弱与梅雨期TC频数存在显著的负相关,达到-0.41。同时,挑选出强梅雨年和弱梅雨年,发现强、弱梅雨异常年的TC特征差异显著,表现在:强梅雨年TC生成较少,以西、西北行为主,主要影响我国南部地区;弱梅雨年TC生成偏多,以转向路径为主,影响我国东南沿海众多省份。此外,两者通过大气环流场相互影响,梅雨期季风槽的位置与强度影响TC生成频数与源地,TC的活动又反作用于梅雨期的环流形式与水汽输送。     

西北太平洋变性台风时空分布特征

利用中国气象局上海台风研究所整编的1961-2000年共40 a热带气旋年鉴资料,对发生在西北太平洋上的变性台风的时空分布特征进行了诊断分析和研究.研究发现,发生于西北太平洋上的变性台风的年频数呈现出明显的年代际变化特征,主要特征是20世纪60年代偏多,70至80年代显著减少,90年代初又略有回升,至90年代下半期每年发生变性的台风个数均极少;年际变化趋势呈现出逐年减少的特征,与西北太平洋上生成的总台风频数的变化趋势一致;西北太平洋上的变性台风多发生于夏、秋两季,特别集中于夏季与秋季的转换时期(变性比例分别达到40%及46%);秋季较夏季台风发生变性的位置整体偏东;台风变性前移动路径主要集中于朝鲜半岛以南及日本海附近,变性后路径多北上偏东;西北太平洋各月变性台风在变性后6小时内平均强度均减弱,变性后12小时内平均强度仍继续减弱,变性后强度加强的气旋的最低平均气压仅在6、7月份较变性前最明显.进一步通过对NCEP/NCAR月平均再分析资料的500 hPa高度场的EOF分析,发现夏、秋两季,纬向环流指数与台风变性频数呈显著负相关;中高纬度500hPa距平高度场在夏半年为正距平区,对应着高压,宜于冷空气入侵向高纬地区北上的台风,促进台风发生变性.     

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.     

A STUDY ON THE VARIATIONS OF CIRCULATION PATTERN IN THE NORTHERN HEMISPHERE AND CLIMATE CHANGE IN CHINA FOR THE RECENT 100 YEARS

The time series of annual frequency of the circulation patterns W,C,E in the Northern Hemisphere and annual mean temperature of Beijing (T_B),Shanghai (T_S) and the whole country (T_C) in the period 1891-1990 are expanded as a long-term tendency,a periodic function and a random function.The coherence between circulation and temperature is calculated and analyzed.The abrupt change of circulation and temperature in the last 100 years is revealed with the methods of the accumulated anomalous curves,the signal/noise ratio as well as the Mann-Kendall test.The correlations between anomalous circulation and climate are discussed with some explanations.