DIAGNOSIS OF THE DEVELOPMENTAL MECHANISM OF THE EXTRATROPICAL TRANSITION OF A TROPICAL CYCLONE USING POTENTIAL VORTICITY INVERSION OF FRONTOGENESIS

This paper diagnoses and analyses the developmental mechanism of a process of extratropical transition of a tropical cyclone which occurred over West Pacific Ocean based on a diagnosis method of potential vorticity inversion of frontogenesis.The study diagnoses quantitatively the role and effect of dynamic influence of westerly cold troughs,middle-latitude baroclinic frontal zones,cyclone cycles and unbalanced wind fields during the different stages of the extratropical transition of a tropical cyclone,and also discusses the interaction between them and the developmental mechanism.The results show that there are different developmental mechanisms during each stage of the extratropical transition and the processes are also unbalanced.     

一种识别热带气旋降水的数值方法

提出了一种有于识别热带气旋降水的数值方法。这一方法是在中国国家气候中心与美国国家气候资料中心的双边合作研究中得以实现的。该方法的识别结果与天气图人工判别结果相比较表明，两者结论十分一致。     

北上变性热带气旋对辽东半岛降水的影响

9711(Winnie)和0509(Matsa)是两个登陆北上影响辽东半岛的变性台风,Matsa直接登陆辽东半岛,但降水量仅为穿过渤海间接影响辽东半岛的Winnie的一半.分析其变性过程与辽东半岛热带气旋降水的关系发现,Winnie和Matsa的降水差异与其北上期间与西风带系统的相互作用密切相关.Winnie变性北上期间被中纬度西风槽"捕获",发生耦合,高层正湿位涡扰动下传,西风带冷空气与热带气旋暖湿气流相互作用,有利于对流云团的生成、发展,在半岛地区产生大暴雨的降水雨带由多个β中尺度云团组成.Matsa在北上变性过程中,只是靠近高空槽底,没有发生耦合,高层正湿位涡扰动不强,没有与低层环流相互作用,冷空气偏南偏弱,变性过程中半岛地区只有1个β中尺度云团生成,降水量较小.     

发生在中国大陆的台风变性加强过程分析

通过对登陆台风Winnie(1997)的演变过程分析，发现登陆后的台风经历三个阶段：衰减阶段、变性阶段、重新加强阶段。其变性过程类似于Sekioka等人提出的复合型，变性后逐渐演变为Shapiro—Keyser气旋模型。通过对物理量的诊断分析发现，对流层中高层冷空气的下沉入侵以及对流层低层的暖平流是热带气旋变性的原因。冷空气的入侵使具有暖心结构的热带气旋演变为斜压结构的温带气旋。变性后气旋得到了重新发展，低层维持的较明显暖平流以及与高空急流相对应的散度区和高空涡度平流是导致气旋重新发展的重要物理因子。     

青藏高原切变线对四川盆地西部突发性暴雨影响的数值试验

使用η模式对１９９５年８月２４日四川盆地西部一次突发性暴雨进行了数值模拟和无高原切变线、无西昌小高压的数值试验。由试验结果分析得出：（１）高原切变线活动可使四川盆地西部暴雨增强，而西昌小高压的存在则便四川盆地西部暴雨减弱；（２）高原切变线活动使暴雨增强的主要机制是暴雨区上空对流层低层流场辐合、上升运动、正涡度、水汽通量辐合和对流层中层流场辐合、水汽通量辐合等的加强；（３）对流层低层的动力、水汽条件     

THE ANALYSIS OF TROPICAL CYCLONE PRECIPITATION AFFECTING THE LIAODONG PENINSULA

1 INTRODUCTION Tropical cyclones (TCs) moving north and getting to the Liaodong Peninsula and waters of the Yellow and Bohai Seas are in their late phase of life cycle.While weakening rapidly, TCs carry a large amount of warm and humid air that forms heavy rainfall by itself on the one hand and interact with westerlies in the middle latitudes on the other.     

影响辽东半岛的热带气旋降水分析

选取移动路径和转向趋势极为相似的两个热带气旋——9711（Winnie）和9406（Tim）为例,对其路径、降水量、移动速度进行对比分析,结果表明,Winnie路径偏东,转向后移动速度增幅大,在辽东半岛地区的降水量大;Tim路径偏西,转向后移动速度增幅小,强降水偏西。并针对其在辽东半岛造成的降水量的差异,采用NCEP全球分析资料,诊断分析其环境流场和结构特征,分析表明,除了地形和海洋的影响,副热带高压位置、高低空急流和锋区与辽东半岛地区的强降水有直接关系。Winnie影响期间,有利、稳定的副高位置使来自东南和西南的暖湿空气输送到辽东半岛上空,并阻挡着低压系统东移出海,使降水持续增加;高低空急流在高空急流人口区上升支环流圈内耦合,对流层上层强辐散场的抽吸作用及高位涡的向下输送,有利于气旋的发展加强;东、西两侧冷空气作用使其变性加强,形成温带气旋,引起强降水。Tim影响期问,副高中心偏西、偏北,高低空急流在高空急流出口区下沉支环流圈内相互作用,其上空辐散强度较弱,只是Winnie的八分之一,不利于气旋的发展加强;Tim位于高空槽后,获得负涡度平流,在东部弱冷空气作用下,引起台风弱变性,并没有形成气旋,在东北地区被西风槽合并后消失,辽东半岛只出现10mm以下的降水。     

THE ANALYSIS OF TROPICAL CYCLONE PRECIPITATION AFFECTING THE LIAODONG PENINSULA

1 INTRODUCTIONTropical cyclones (TCs) moving north and gettingto the Liaodong Peninsula and waters of the Yellowand Bohai Seas are in their late phase of life cycle.While weakening rapidly, TCs carry a large amount ofwarm and humid air that forms heavy ra…     

对流云团资料在局地暴雨数值模拟预报中的应用

使用ＰＳＵ／ＮＣＡＲ中尺度数值模式,对两次暴雨实例进行了数值模拟试验。结果表明：相对应用地面及高空常规资料作为初始场的控制试验而言,就用实时卫星对流云团资料增强局部湿度场的敏感性试验,可使暴雨及邻近地区对流层中低层气流辐合上升运动增强,     

减弱热带气旋附近的倾斜涡度发展

根据1998年北半球夏季6、7、8月逐月500hPa高度场实测资料,利用具有双重筛选功能的二维空间谱分析方法,分别获得了能大致反映1998年北半球6、7、8月500hPa高度场分布特征的3组空间波集,每组包含15个空间波。分别利用这3组空间谱函数,从Galerkin途径出发,获得了1998年长江流域夏季降水异常的一个物理机制:在前期典型ElNi?o型海温异常,以及5月后ElNio型海温异常减弱,Lania型海温异常分布建立的这些外部异常热力强迫作用下,导致大气环流出现不同的非线性内部动力过程,6月大气环流演变中波波相互作用和波流相互作用较弱,7、8月的大气环流演变中尽管波波相互作用明显,但波流相互作用仍然很弱。波流相互作用的持续偏弱,导致了1998年夏季西太平洋副热带高压位置持续偏南,夏季强降雨带持续稳定于长江流域。     

“相空间”方法判断西北太平洋热带气旋变性适用性研究

大部分热带气旋进入中纬度地区都会发生向温带气旋的转变。这一变性过程会造成强降水和大风，并且移速增快，因此给中纬度地区造成很大的灾害。西北太平洋地区热带气旋变性是一个与中纬度系统相互作用的复杂过程，判断其变性与否是一个关键性问题。详细介绍了判定TC变性的“相空间”方法，该方法包含了三个参数：对流层低层热力对称性参数、高层热成风参数、低层热成风参数。使用“相空间”方法对2000—2007年间西北太平洋地区TC的变性过程进行统计分析，以验证此种方法在西北太平洋地区的适用效果。结果表明，“相空间”方法对判定西北太平洋地区TC有一定指示作用，但该方法作为业务应用还存在一定问题。     

THE STRUCTURE OF TROPICAL CYCLONE BY TOVS AND ITS APPLICATION IN NUMERICAL WEATHER PREDICTION

The TOVS data are used to study the structure of a number of tropical cyclones for the year 2000. Differences are found to some extent between what is found and classic conceptual models in that (1) the horizontal structure is asymmetric and variable so that the low-value centers at low levels of the geopotential height field (or the high-value centers at high levels) do not necessarily coincide with the high-value centers of the temperature field; (2) the vertical structure is also variable in the allocation of the anomalies of the geopotential height field between low values at low levels and high values at high levels. It is especially noted that the centers of the anomalies are tilting at both high and low levels or the high level is only at the edge of a high-pressure zone. There is not any significant high-value anomalous center in a corresponding location with the tropical cyclone. The structure of tropical cyclone in the TOVS is also used as reference to modify the structure of typhoon BOGUS in the numerical prediction model system of tropical cyclones. It is found that the modified BOGUS performs better in coordinating with the environment and predicting the track of the tropical cyclone. The demonstration is two-fold — the structure of the typhoon BOGUS is such that it means much in the track prediction and the use of the TOVS-based tropical cyclone structure really helps in improving it. It provides the foundation for modification and evolution of typhoon BOGUS.     

鲁中山区地形对山东省一次暴雨影响的敏感性数值模拟试验

利用PSU/NCAR MM5V3中尺度数值模式进行了鲁中山区地形对一次台风暴雨的数值模拟敏感性试验,结果分析表明:鲁中山区地形作用对山东省暴雨有重要影响,迎风坡可引起低层气流和水汽的辐合上升运动增强,降水量增加,但偏北气流在迎风坡的水汽辐合不明显,降水量影响不大;山顶引起低层辐合上升运动减弱,辐散下沉运动增强,降水量减小;背风坡引起低层气流和水汽的辐合上升运动增强,降水量增加。     

卫星资料在台风暴雨数值模拟中的应用

用ＰＳＵ／ＮＣＡＲ中尺度模式，采用ＥＣＭＷＦ资料对８２０９号台风带来的暴雨进行了控制试验，同时采用卫星和地面资料对原有初始湿度场作订正，进行了灵敏试验。对比分析表明，应用卫星资料后，模拟的台风暴雨及雨量中心强度与实况甚为一致。此外，由模式输出流场的分析表明，台风内部及其外围有显著的非对称气流和明显的中尺度系统结构。暴雨发生在低空非对称气流聚合和高空非对称气流辐散重叠区域；在强雨量中心区，低空有清楚     

THE EFFECTS OF STATION NETWORK DENSITY ON STATISTICAL ANALYSES OF TROPICAL CYCLONE PRECIPITATION

In this paper, 1416 conventional ground-based meteorological observation stations on the mainland of China were subdivided into groups of differing spatial density. Data from each subgroup were then used to analyze variations in the tropical cyclone (TC) precipitation statistics derived from each subgroup across the mainland of China (excluding Taiwan, Hong Kong, and Macao), as well as in two regions (east China and south China) and three provinces (Guangdong, Hainan, and Jiangxi) between 1981 and 2010. The results showed that for the mainland of China, total precipitation, mean annual precipitation, mean daily precipitation, and its spatial distribution were the same regardless of the spatial density of the stations. However, some minor differences were evident with respect to precipitation extremes and their spatial distribution. Overall, there were no significant variations in the TC precipitation statistics calculated from different station density schemes for the mainland of China. The regional and provincial results showed no significant differences in mean daily precipitation, but this was not the case for the maximum daily precipitation and torrential rain frequency. The maximum daily precipitation calculated from the lower-density station data was slightly less than that based on the higher-density station schemes, and this effect should be taken into consideration when interpreting regional climate statistics. The impact of station density on TC precipitation characteristics was more obvious for Hainan than for Guangdong or Jiangxi provinces. In addition, the effects were greater for south China (including Guangxi Zhuang Autonomous region, Guangdong, and Hainan provinces) than east China (including Shandong, Jiangsu, Zhejiang, Shanghai, Fujian, Anhui, and Jiangxi provinces). Furthermore, the analysis proved that the statistical climatic characteristics began to change significantly when the station spacing was between 40 and 50 km, which are close to the mean spacing for all stations across the mainland of China. Moreover, TC areal precipitation parameters, including mean total areal precipitation and mean daily areal precipitation, also began to change significantly when the spacing was between 40 and 50 km, and were completely different when it was between 100 and 200 km.     

THE USE OF RADAR DATA IN THE NUMERICAL SIMULATION OF HEAVY RAINFALLS IN THE CHANGJIANG-HUAIHE RIVER BASIN

It is important for predictions of heavy rainfall to include radar data to provide better reflection of moisture. Numerical experiments were carried out with real cases of heavy rains in the Changjiang (Yangtze)-Huaihe River Basin using a PSU/NCAR mesoscale model that incorporated radar data. Processed radar data were added to the model to change the analysis of initial humidity field before 24-h numerical simulations were made and the results compared with a control experiment. It is suggested that the radar-data-incorporated numerical predictions could produce locations of precipitation areas and maximum rainfall that are closer to reality than the control, due to the fact that moisture and converging updraft are strengthened in the middle and lower levels of the troposphere in the area of heavy rains and areas nearby. The work is expected to improve numerical modeling and forecasts of heavy rains in middle and lower latitudes of China.     

一次江淮暴雨过程中中尺度气旋的数值模拟及分析

本文利用PSU／NCAR中尺度数值模式MM5,并利用鄂、豫、皖、苏四省的加密地面气象要素场资料做检验,对1991年7月6日江淮地区发生的一次暴雨过程进行了分析。结果表明：江淮暴雨过程中的中尺度气旋在发生、发展、变化过程中其结构具有不对称性,因而进一步造成了局地降水强度和分布的不均匀性。而中尺度气旋的结构不对称性又与其地面及高空的流场、涡度场及散度场等的中尺度特征有直接的联系。     

台风移速突变的数值研究

用准地转正压模式，在无环境气流的情况下，实施了８组时间积分大于５个模式日的试验。在模式大气台风移动的过程中，清楚地显示了移速突然变化的现象。台风移速突然变化与前期台风环流的非对称结构之间存在着密切的联系。最后分析了台风环流非规则结构对路径的影响。     

APPLICATION OF AN OBJECTIVE DISCRIMINATING METHOD IN THE EVOLUTION OF TROPICAL CYCLONE "HAIMA" DURING EXTRATROPICAL TRANSITION

An objective method for discriminating the process of extratropical transition (ET) in tropical cyclones is introduced. With this method, the gridpoint output data of NWP are used to calculate three parameters: storm-relative thickness symmetry (B), low-level (-VLT) and upper-level thermal wind (-VUT). This objective method is easy to calculate and convenient for operational use. To verify the method, this paper uses the NCEP reanalysis data to identify the evolution of ET for "Haima", a tropical storm (0421) that affected the eastern part of China in 2004. The result shows that the three parameters defined with the objective method are good indicators of the ET process.     

暴雨中尺度气旋发展的等熵面位涡分析

利用中尺度模式ＭＭ４对１９９１年７月５～６日的江淮梅雨锋暴雨过程进行了数值模拟。用模式输 出资料，根据湿位涡理论分析了这次暴雨过程中对流层低层的中尺度低涡及地面气旋发生发 展的原因。结果表明，在有利的等熵面形态下，具有较高湿位涡值的高层冷空气沿等熵面快 速向南下降的过程中绝对涡度增加，导致了气旋性涡旋的发展加强。