一次江淮气旋暴雪的积雪特征及气象影响因子分析

利用自动站、人工加密观测及常规观测资料,通过对2017年2月21—22日一次江淮气旋暴雪过程积雪特征的分析,揭示了近地面气象要素对积雪深度的复杂影响。结果表明:(1)江淮气旋系统特有的空间结构导致山东南、北地区的降雪量和积雪深度不均衡分布。(2)积雪深度具有时效性,在降雪结束时达到峰值,因温度的变化导致峰值不一定维持到次日08时。(3)积雪深度是近地面多气象要素共同作用的结果,降水相态、降雪量、降雪强度、气温、地温和风速均有影响。主要表现为:雨夹雪在转为纯雪之前可产生不超过1 cm的积雪,如果不转雪则不会产生有量积雪;各地降雪含水比差异较大,全省平均为0. 5 cm·mm~(-1),低于全国平均值;在降雪不融化的情况下,降雪量、降雪强度越大则积雪越深,降雪强度大是气温和地温都高于0℃时产生积雪的必要条件;地温和气温越低对积雪形成越有利,积雪开始产生时的地温最高阈值多在0℃左右,地温先突降后缓升是积雪产生前后的共性特征,积雪产生后1～2 h内地温略有上升并逐渐趋于稳定;积雪产生时气温一般低于0℃,气温高于0℃时大部分降雪融化;有利于产生积雪的平均风力多不超过2级,极大风则在3～4级以下。     

Assessing the Influence of the ENSO on Tropical Cyclone Prevailing Tracks in the Western North Pacific

Using a statistical model for simulating tropical cyclone (TC) formation and a trajectory model for simulating TC tracks, the influence of the El Nino-Southern Oscillation (ENSO) on the peak-season (July-September) TC prevailing tracks in the western North Pacific basin is assessed based on 14 selected El Nino and 14 selected La Nina years during the period 1950-2007. It is found that the combination of statistical formation model and a trajectory model can simulate well the primary features of TC prevai...     

台风异常运动及其外区热力不稳定非对称结构的影响效应

本文数值模拟研究揭示了台风外区热力不稳定非对称结构对其异常路径的影响问题，提出了台风运动非对称结构的影响，不仅表现在台风涡旋动力结构特征上，而且反映在台风外区三维非对称热力结构特点方面，即包括温、湿不稳定层结分布特征及其强弱程度因素。台风外区不同热力非对称分布特征将导致台风移动轨迹的显著差异，且构成各类“旋转”、“打转”、“转向”等复杂异常路径。     

Influence of future tropical cyclone track changes on their basin-wide intensity over the western North Pacific: Downscaled CMIP5 projections

The possible changes of tropical cyclone(TC) tracks and their influence on the future basin-wide intensity of TCs over the western North Pacific(WNP) are examined based on the projected large-scale environments derived from a selection of CMIP5(Coupled Model Intercomparison Project Phase 5) models. Specific attention is paid to the performance of the CMIP5 climate models in simulating the large-scale environment for TC development over the WNP. A downscaling system including individual models for simulating the TC track and intensity is used to select the CMIP5 models and to simulate the TC activity in the future.The assessment of the future track and intensity changes of TCs is based on the projected large-scale environment in the21 st century from a selection of nine CMIP5 climate models under the Representative Concentration Pathway 4.5(RCP4.5)scenario. Due to changes in mean steering flows, the influence of TCs over the South China Sea area is projected to decrease,with an increasing number of TCs taking a northwestward track. Changes in prevailing tracks and their contribution to basin-wide intensity change show considerable inter-model variability. The influences of changes in prevailing track make a marked contribution to TC intensity change in some models, tending to counteract the effect of SST warming. This study suggests that attention should be paid to the simulated large-scale environment when assessing the future changes in regional TC activity based on climate models. In addition, the change in prevailing tracks should be considered when assessing future TC intensity change.     

我国热带气旋灾害的分析研究

本文对１９４９—１９９１年４３年的热带气旋资料，以及１９５６—１９９２年３７年的热带气旋灾情资料进行了分析，说明了热带气旋灾害的主要特征和发展趋势。提出了关于热带气旋灾情评估的３项指标，表明灾情与热带气旋系统强度、大小、天气，登陆率，预报准确率，热带气旋系统影响地区社会经济活动的发达程度，物质财富积累水平，以及防抗措施的水平等有密切的关系，为我国今后防台减灾提供了依据。     

夏季亚洲-太平洋涛动与中国近海热带气旋活动的关系

采用联合台风警报中心的台风最伟路径资料和NCEP/NCAR再分析资料,分析了夏季亚洲-太平洋涛动(Asian-Pacif-ic Oscillation,简称APO)与东亚近海-西北太平洋大气环流的关系,并进一步探讨了APO与中国近海热带气旋(tropical cy-clone,简称TC)活动的关系.研究表明:(1)夏季APO强弱与同期西北太平洋及中国东部近海TC活动存在密切关系,即在APO强(弱)年,西北太平洋TC活动偏西(东)和偏北(南),中国东部近海TC明显增多(减少);(2)当APO偏强(弱)时,中国东部近海大气环流有(不)利于TC的维持和发展,表现为低层存在异常气旋性(反气旋性)环流,对流层高低层纬向风垂直切变减小(增大),且对流加强(减弱);(3)APO强弱也影响着TC引导气流的方向:在APO强(弱)年,西北太平洋副热带高压(以下简称副高)偏北和偏东(偏南和偏西),副高南侧偏东气流减弱(加强),有利于TC的向西北行或在偏北(南)纬度西行,进入中国东部近海的TC增多(减少);(4)APO强弱也影响着南海-热带西太平洋TC源地上空的大气环流,在APO强(弱)年,南海-热带西太平洋季风槽偏北、偏西(偏南、偏东),热带西太平洋TC活动偏北和偏西(偏南和偏东),有利于进入中国东部近海TC的增多(减少).     

ANALYSIS OF STRUCTURE EVOLUTION AND ENVIRONMENTAL CONDITIONS OF TROPICAL CYCLONES OVER THE WESTERN NORTH PACIFIC DURING EXTRATROPICAL TRANSITION

Fifty-eight extratropical transition (ET) cases in the years 2000-2008, including 2,021 observations (at 6-hour intervals), over the western North Pacific are analyzed using the cyclone phase space (CPS) method, in an effort to get the characteristics of the structure evolution and environmental conditions of tropical cyclones (TCs) during ET over this area. Cluster analysis of the CPS dataset shows that strong TCs are more likely to undergo ET. ET begins with the increment of thermal asymmetry in TCs, along with the generation and intensification of an upper-level cold core, and ends with the occurrence of a lower-level cold core. ET lasts an average duration of about 28 hours. Dynamic composite analysis of the environmental field of different clusters shows that, in general, when TCs move northward, they are gradually embedded in the westerlies and gradually transform into extratropical cyclones under the influence of the mid- and higher-latitude baroclinic systems. As for those TCs which complete ET, there is always much greater potential vorticity gradient in the northwest of them and obvious water vapor transport channels in the environment.     

2007年西北太平洋热带气旋活动综述

利用热带气旋年鉴、海温和大气环流再分析资料,分析2007年西北太平洋(包括南海)的风暴级以上热带气旋(简称TC)活动状况及海-气条件.结果表明,相对于气候平均值,2007年西北太平洋TC活动的季节峰期推后了约2个月,源地明显偏北,生成点纬度发生了2次明显跃变,年度TC的总体活动较弱,但个体的强度较强,路径以西北行为主,登陆比例偏大.影响上述TC活动特征的一个重要原因是年内ENSO循环的位相使得上半年的大气环流不利因素居多,而下半年大尺度上升运动、热带辐合带均较强,副高偏北、局地垂直风切变较小和对流层低层较强的扰动活动等条件,也十分有利热带气旋活动.     

西北太平洋热带气旋变性过程中的风及降水分布变化特征分析

利用中国气象局上海台风研究所（CMA/STI）整编的热带气旋最佳路径资料、美国飓风联合警报中心（JTWC）最佳路径资料、美国国家海洋与大气管理局（NOAA）的全球多平台热带气旋风场资料（MTCSWA）和CMORPH降水资料、日本卫星云顶黑体辐射温度（T_BB）资料等,分析1987～2016年30年间西北太平洋228个变性热带气旋（ETTC）的活动规律、风与降水分布及其演变特征。结果表明:（1）ETTC年均7.6个,除1～2月,各月均有分布,峰值在9月。约90.4%的ETTC变性位置在30°N以北,仅约9.6%在30°N以南较低纬度,且多发生于春夏和秋冬交替季节。（2）TC（热带气旋）变性通常发生在其转向后,半数以上移速加快,大多数中心气压升高或维持,仅10.5%降低。（3）变性过程中ETTC近中心最大风速减小,最大风速半径增大,内核趋于松散。其34节风圈半径北侧明显大于南侧,风场结构非对称性增强。（4）ETTC强风和强降水呈显著非对称性分布,其强风区主要出现在ETTC中心东侧,即路径右后方;强降水区主要出现在北侧,且变性后在东北象限向外扩张。（5）较强的环境水平风垂直切变（VWS）是影响ETTC风及降水分布的重要因子。强降水主要出现在顺风切方向及其左侧,强风（去除TC移速时）出现在切变左侧。     

Experiments with the Improved Dynamical-Statistical-Analog Ensemble Forecast Model for Landfalling Typhoon Precipitation over South China

In recent work, three physical factors of the Dynamical-Statistical-Analog Ensemble Forecast Model for Landfalling Typhoon Precipitation (DSAEF_LTP model) have been introduced, namely, tropical cyclone (TC) track, TC landfall season, and TC intensity. In the present study, we set out to test the forecasting performance of the improved model with new similarity regions and ensemble forecast schemes added. Four experiments associated with the prediction of accumulated precipitation were conducted based on 47 landfalling TCs that occurred over South China during 2004-2018. The first experiment was designed as the DSAEF_LTP model with TC track, TC landfall season, and intensity (DSAEF_LTP-1). The other three experiments were based on the first experiment, but with new ensemble forecast schemes added (DSAEF_LTP-2), new similarity regions added (DSAEF_LTP-3), and both added (DSAEF_LTP- 4), respectively. Results showed that, after new similarity regions added into the model (DSAEF_LTP-3), the forecasting performance of the DSAEF_LTP model for heavy rainfall (accumulated precipitation ≥250 mm and ≥100 mm) improved, and the sum of the threat score (TS250 + TS100) increased by 4.44%. Although the forecasting performance of DSAEF_LTP-2 was the same as that of DSAEF_LTP-1, the forecasting performance was significantly improved and better than that of DSAEF_LTP-3 when the new ensemble schemes and similarity regions were added simultaneously (DSAEF_LTP-4), with the TS increasing by 25.36%. Moreover, the forecasting performance of the four experiments was compared with four operational numerical weather prediction models, and the comparison indicated that the DSAEF_LTP model showed advantages in predicting heavy rainfall. Finally, some issues associated with the experimental results and future improvements of the DSAEF_LTP model were discussed.