Factors contributing to the development of extreme North Atlantic cyclones and their relationship with the NAO

The occurrence of extreme cyclones is analysed in terms of their relationship to the NAO phase and the dominating environmental variables controlling their intensification. These are latent energy (equivalent potential temperature 850 hPa is used as an indicator), upper-air baroclinicity, horizontal divergence and jet stream strength. Cyclones over the North Atlantic are identified and tracked using a numerical algorithm, permitting a detailed analysis of their life cycles. Extreme cyclones are selected as the 10% most severe in terms of intensity. Investigations focus on the main strengthening phase of each cyclone. The environmental factors are related to the NAO, which affects the location and orientation of the cyclone tracks, thus explaining why extreme cyclones occur more (less) frequently during strong positive (negative) NAO phases. The enhanced number of extreme cyclones in positive NAO phases can be explained by the larger area with suitable growth conditions, which is better aligned with the cyclone tracks and is associated with increased cyclone life time and intensity. Moreover, strong intensification of cyclones is frequently linked to the occurrence of extreme values of growth factors in the immediate vicinity of the cyclone centre. Similar results are found for ECHAM5/OM1 for present day conditions, demonstrating that relationships between the environment factors and cyclones are also valid in the GCM. For future climate conditions (following the SRES A1B scenario), the results are similar, but a small increase of the frequency of extreme values is detected near the cyclone cores. On the other hand, total cyclone numbers decrease by 10% over the North Atlantic. An exception is the region near the British Isles, which features increased track density and intensity of extreme cyclones irrespective of the NAO phase. These changes are associated with an intensified jet stream close to Europe. Moreover, an enhanced frequency of explosive developments over the British Isles is found, leading to more frequent windstorms affecting Europe.

山东中西部一次超级单体分裂过程的雷达回波结构和环境条件分析

利用常规观测资料、济南多普勒雷达资料、FY-2G资料和加密自动站等资料分析了2016年6月14日一次在华北冷涡背景下发生的超级单体风暴生成及分裂过程,对超级单体分裂过程的雷达回波特征和环境条件进行了详细的分析。结果表明,超级单体风暴发生在地面中尺度辐合线附近,中层短波槽前,高空有中空急流的环境下,触发的对流云团向偏东方向移动中,在不稳定层结和较强的垂直风切变作用下,对流风暴发生分裂且右移性对流风暴发展加强。风暴分裂后环境风左侧的风暴单体并没有受到明显抑制,中尺度辐合线附近的露点锋生抵消了反气旋性风暴的受抑制程度,使反气旋性风暴能有所加强并持续更长的时间。环境风右侧的风暴单体发展加强,且持续时间长达2 h。风暴分裂是在单体发展的初期开始,分裂先从中高层开始,然后向下延伸,分裂后相对于环境风方向,左侧单体为反气旋性左移风暴,右侧为气旋性右移风暴。气旋性右移风暴强烈发展为具有低层的入流缺口、中高层的弱回波区及风暴顶的强辐散,与经典超级单体风暴回波特征类似。分裂后右移风暴伴有深厚持久的中气旋,其起源于中层4～5 km,然后向上和向下发展,最强旋转出现在高层,旋转速度达29 m/s,这与典型超级单体内中气旋都是中层旋转最强有所不同。     

Recent Sea Level and Sea Surface Temperature Trends Along the Bangladesh Coast in Relation to the Frequency of Intense Cyclones

The French Transportable Laser Ranging System (FTLRS) was deployed in the calibration site of satellite radar altimeters in Corsica over the 2002 and 2005 campaigns. The paper describes the different steps of SLR data processing. The average arcs RMS obtained are about 1–2 cm for Lageos-1&;-2, Starlette and Stella satellites; it is shown that the best results of satellite orbits determination and geocentric positioning are obtained with Eigen-Grace03s gravity model. The difference of FTLRS absolute 3D positioning, between 2002 and 2005, of about 7.7 mm (i.e., 2.6 mm/yr) is less than residual errors of ITRF2005 velocities (of about 4.3 mm/yr).     

基于Cyclone和PolyWorks的三维建模实现

从数据采集到数据处理,再到最后的模型重建,以实例详细介绍了地面激光扫描三维建模的整个流程。利用LeicaHDS6000地面激光扫描仪进行点云数据采集,针对规则和不规则建筑物的特点,分别基于Cyclone和PolyWorks软件实现了三维建模。     

“2.28”山东罕见“雷打雪”现象形成机制分析

利用各种常规观测资料、探空资料、T639模式资料和卫星云图,分析了2010年2月28日山东境内的一次罕见"雷打雪"过程。结果表明,此次过程是在有利的大尺度环流背景下产生的。西南暖湿气流强盛,对流层低层的低空急流不断向山东输送水汽和能量;同时,近低层冷空气的侵入,迫使暖湿空气沿冷空气爬升,触发不稳定能量释放,导致强对流天气发生。850hPa低涡及地面气旋的产生,使得气旋性辐合上升增强,加强了上升运动。随着近地层温度降到零度以下,雨转雪。降水过程后期,气旋向东北方向移动,造成鲁中和山东半岛的暴雪天气。卫星云图显示,MCC是造成此次强降水的直接原因。     

气旋波动研究进程及研究方法

较全面地回顾与阐述了气旋波动研究进程及研究方法, 其中包括Bjerknes气旋模式, 以及Bjerknes and Solherg (1922) 提出的温带气旋生命循环和Petterssen (1956) 对气旋温度结构的描述, 并指出凝结潜热及地形对气旋发展的作用。还较详细地介绍了Petterssen (1956) 气旋发展理论、倾斜涡度发展理论、来自准地转 方程及位涡思考的气旋生成理论, 以及高空超长波系统发展与高空急流加强有利于低层爆发性气旋发展的学术观点, 为气旋的研究提供了历史研究背景、研究思想及方法。     

利用雷达回波特征和地面资料确定0312号台风"科罗旺"强度

通过分析0312号台风"科罗旺"过程的雷达回波特征和地面资料,应用"热带气旋强度综合判据表"的办法,确定该台风的强度,并分析其大风分布的特点.为将来雷达探测台风业务,分析回波资料积累一些经验和方法,从而能更好的利用雷达回波应用于台风预报业务.     

Analyses of Orissa Super Cyclone using TRMM (TMI), DMSP (SSM/I) and OceanSat-I (MSMR) Derived Data

The super cyclone in October 1999 was the most intense tropical cyclone in the last century in Orissa, a coastal state in India. This state was battered for more than two days by strong winds and intense rain killing thousands of people. The main objective of this study is to examine the impact of total precipitable water content (TPWC) and surface wind speed data from sensors on board the Tropical Rainfall Measuring Mission (TRMM), Defense Meteorological Satellite Project (DMSP), and Indian Remote Sensing Satellite (OceanSat-I) satellites on the data assimilation system at NCMRWF, New Delhi during the Orissa cyclone period. Comparison of various assimilation experiments suggests that the utilization of TRMM Microwave Imager (TMI) data in the assimilation produced the best analyses. However, in all the forecasts, the storm was predicted to weaken and did not have a reasonably good track. Assimilation experiments with the other two satellite data showed the cyclone track much to the south of the observed track and also it was a weak storm. Biases in the data, when compared with each other, are evident in the analyses also. Better analyses are obtained when the satellite data are used in the originally obtained resolution than when reduced by averaging. A forecast experiment with assimilated data, utilizing the Cloud Motion Vectors (CMVs) from METEOSAT along with TMI data, produced the best forecast among all the experiments. However, the forecast quality was poor. A high-resolution data assimilation experiment was carried out to see the impact of model resolution on the analyses of the cyclone. The strength of the cyclone further increased when higher resolution TMI data were included. The study highlights the need for more satellite data over the Indian Ocean, where conventional data coverage is too poor to define the vertical structure of the atmosphere.     

用地理信息系统改进热带气旋的客观定位精度

基于地理信息系统(Geographic Information System，简称GIS)技术，初步建立了一个能集成多种数据资料和多种算法的热带气旋(Tropical Cyclone，简称TC)客观定位系统。其中不同卫星及同一卫星不同波段资料(如Quikscat洋面风场、云顶亮温等)的矢量及栅格信息的叠加和分析功能，有助于从多个侧面揭示TC的结构特征；而多种定位方法(如云图形态分析法、云顶亮温极值法、洋面风场涡度极值法、数学形态学算法等)的客观化及其综合运用的实现，不仅可以减小TC定位过程中的随机(人为)误差，而且能提高TC定位工作的效率。利用该系统对编号为0203，0209，0212，0417和0419的5个TC进行的定位试验结果表明:利用该系统进行TC定位的精度与目前业务定位精度相当，具有良好业务应用前景。     

人工神经网络与符号推理在江淮气旋预报中的应用研究

本文通过对符号推理及神经网络系统的剖析，实现了神经网络与符号推理的有机结合，并成功地运用到天气预报中去。提出了一种新的，充分利用预报经验，数值预报产品及计算机计算能力的预报方法。