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11.
It has long been known that incipient tropical cyclones (TCs) always occur in
synoptic-scale disturbances or tropical cyclogenesis precursors, and the disturbances can
intensify only within a limited area during tropical cyclogenesis. An observational analysis
of five tropical cyclogenesis events over the western North Pacific during 11 August to 10
September 2004 is conducted to demonstrate the role of synoptic-scale disturbances in
establishing a limited area of low-deformation vorticity for tropical cyclogenesis.
The analysis of the five tropical cyclogenesis events shows that synoptic-scale tropical
cyclogenesis precursors provide a region of low-deformation vorticity, which is measured with
large positive values of the Okubo-Weiss (OW) parameter. The OW concentrated areas are within
the tropical cyclogenesis precursors with a radius of about 400-500 km and can be found as
early as 72 hours prior to the formation of the tropical depression. When the TCs reached the
tropical storm intensity, the concentrated OW is confined to an area of 200-300 radius and the
storm centers are coincident with the centers of the maximum OW. This study indicates that the
tropical cyclogenesis occurs in the low-deformation 18-72 hours prior to the formation of
tropical depressions, suggesting the importance of low-deformation vorticity in pre-existent
synoptic-scale disturbances. Although the Rossby radius of deformation is reduced in TC
genesis precedes, the reduction does not sufficiently make effective conversion of convective
heating into kinetic energy within the low-deformation area. Further analysis indicates that
the initial development of four of the five disturbances is coupled with the counterclockwise
circulation of the mixed Rossby-Gravity (MRG) wave. 相似文献
12.
1720号台风"卡努"在南海活动期间,浙江东北部地区出现暴雨,降雨持续时间和强降雨带移动轨迹是本次暴雨预报的难点。利用常规观测和自动站加密观测资料、卫星云图资料及NCEP再分析资料,综合诊断分析了此次暴雨过程的成因和预报难点。结论如下:本次浙江东北部降雨过程分14日08:00至15日13:00和15日14:00至17日08:00两个阶段,第一阶段是"卡努"台风倒槽顶部东南气流和东北气流汇合,以及弱冷空气参与影响造成的降雨,随着"卡努"的西移,雨区随之西移;第二阶段是低层低压环流发展,且低层有强的水汽输入和辐合造成的暴雨,强降雨区随着低压系统一起东北移。低层水汽收入及其增减,对于降雨的开始及增强或减弱有6~12 h的提前。850 h Pa水汽通量值在25 g·h Pa~(-1)·cm~(-1)·s~(-1)以上,水汽通量散度值在-20 g·h Pa~(-1)·cm~(-2)·s~(-1)以下,对应区域接下来的6~12 h有强降雨。垂直螺旋度正值比较大,对应的浙江东北部地区有很强的流体旋转,且对流系统中有涡度输入,该地区之后6 h将出现强降雨。Q*散度负值对强降雨有6~12 h的提前预示。 相似文献
13.
季风槽中热带气旋生成初期扰动的扰动动能收支分析 总被引：4，自引：3，他引：1
热带气旋总是发生在天气尺度扰动中,本文利用NCEP/NCAR提供的FNL资料,选取了2004年8月11日—9月10日期间季风槽中5个热带气旋生成初期扰动,通过计算动能收支分析这些初期扰动的发展。其中4个热带气旋都是生成在向西北方向传播的天气尺度波列的气旋性环流中,气旋性环流可以和呈东北—西南方向倾斜西传的MRG波的逆时针环流耦合。动能收支计算表明,初期扰动动能在热带气旋生成前12~72 h不断增加,扰动位势通量的辐合对扰动动能增长起了主要作用。在季风槽东端的合流区时,能量聚集项有重要作用,随着扰动移入季风槽内,低频纬向风切变项成为能量增加的一个重要来源。Sarika生成于季风槽西撤阶段,非线性作用项对扰动发展起了关键作用。 相似文献
15.
介绍了在自研的《气象雷达基数据结构分析软件》的基础上，通过空间三维插值方法和VTK（Visualization Toolkit）图形图像库显示技术，实现天气雷达基数据三维可视化的功能，该软件可运行于多种操作系统。三维重建功能支持多项交互式操作，能够快速突出雷达回波的结构特征：允许在雷达平面图上选定任意矩形区域进行三维重建；支持地形和雷达回波的叠加；具备缩放、漫游和视角变换功能；提供不同数值区间的透明度和光照系数调整；实现多种类型的切面视图和三视图。最后，本文结合软件在强对流单体、台风等个例中的应用情况，展示了三维重建功能如何帮助预报员快速掌握风暴结构及其演变规律。 相似文献