多普勒天气雷达探测揭示的台风云娜(Rananim) 登陆前后特征演变研究*

温州多普勒天气雷达(CINRAD-SA)建于面临东海的大罗山顶(海拔714m),探测环境较好,它对0414号台风云娜(Rananim)进行了系统性跟踪探测,取得了完整的基数据资料。应用该多普勒天气雷达连续探测资料,配合地面中尺度自动站加密观测资料,通过云娜台风登陆前后的螺旋云带、台风"眼"眼壁、垂直累积含水量和降水量与眼区速度谱宽、台风内中尺度环流等分析,研究了登陆前后台风强度和雷达径向速度的演变特征;同时使用MM5(V3.6)中尺度数值模式结合雷达数值产品分析,就地形对台风演变特征的影响进行了研究,初步揭示了地形影响的一些主要演变特征。研究发现:云娜台风中心登陆之前,位于海上的台风"眼"眼壁在8km高度以下基本垂直,在8km高度以上"眼"的直径明显增大。当台风登陆时,由于受地形影响,其眼壁出现向前或向右前方倾斜,台风"眼"内回波由低层向高层"填塞"。台风眼"填塞"后,台风环流重又加强,使得强回波主体(＞35dbz)仍可保持眼壁轮廓并能持续相当一段时间,这一现象在数值试验中得到了证实;在台风暴雨系统中垂直累积液态水含量(VIL)相同时,由于液态水含量的密实程度不同"降水效率"差异极大,有时可使降水量的差异达到2.5倍甚至更大;台风登陆时,眼壁速度谱宽急剧变化,从到达陆地眼壁前部的低层起到高层增大。多普勒速度谱宽的这种变化与低空西南急流的维持与否相一致。在3~5km高度以上,谱宽较为稳定,表明该高度层的西南急流稳定维持;台风登陆时,受到地形和山脉影响,最大风速半径及台风环流强度随时间的推延,低层最大环流中心移速减慢、最大风速半径开始缩小;台风暴雨的降雨强度与其气旋性涡旋的动力辐合上升强度趋于一致,从多普勒径向速度场产品可以直观地识别、判断和分析辐合辐散运动与冷暧平流的迭加风场。强降水区集中在台风的右前侧,与台风回波强度的不对称结构相一致,并有明显的"眼"的形状。台风环流在乐清砩头、永嘉中堡附近喇叭口状地形幅合作用显著;东南气流与北雁荡山脉形成的较大夹角,对暖湿气流强迫抬升作用十分明显。

THE DEVELOPMENT CHARACTERISTICS OF THE TYPHOON RANANIM BEFORE AND AFTER LANDFALLING DETECTED BY THE DOPPLER WEATHER RADAR

The Doppler Radar (CINRAD-SA), which is located at the peak of the Mountain Daluo (altitude 714m) and facing to the East China Sea in Wenzhou, Zhejiang Province, has recorded almost a complete set of data through trail-detecting on the 0414 Typhoon Rananim. By combining this set of data with the intensely observed data from medium-scale automatic meteorological stations, the development characteristics of Rananim, including its intensity and radial velocity have been described by analyzing the spiral cloudy belt, radar echo of the typhoon eye wall, vertically integrated liquid (VIL), precipitation, width of spectrum in typhoon eye, and inner medium-scale circulation from its pre-thorough post-landfalling. Simultaneously, the impact of topography on the development characteristics of Rananim has been also analyzed by MM5(V3.6) numerical model and radar numerical products. Following are some main results:(1) Before landfalling, the eye wall of Rananim sustained nearly upright below the height 8km above sea level, while over 8km the radius increased markedly. After landfalling, affected by the land topography the eye wall inclines to front or partial-right direction and the echo fills the eye from the lower level to the higher, which results in typhoons circulation being intensified and the eye wall shape being kept for long time by the main body of strong echo (＞35dbz).(2) Different densities of VIL although with the same VIL content will cause obviously different precipitations in the typhoon rainfall system.(3) After landfalling, the spectrum width of eye wall’s speed changed drastically which is in line with the change of storm intensities. (4) After landfalling, affected by land topography, the speed of the largest circulation center in the lower level was gradually slowed down and the maximum wind speeds radius also shrinked.(5) The intensity of typhoons rainfall is geared to the motive convergences ascending intensity of cyclonic vortex.(6) The storm precipitation occurs at the front-right side of Rananim, which is in line with the asymmetrical structure of its echo intensity. The area of precipitation is obviously shaped in an eye place.