冷空气侵入台风“珍珠”的多普勒雷达回波特征

DOPPLER RADAR ECHO CHARACTERISTICS FOR COLD AIR INTRUDING INTO TYPHOON CHANCHU

利用汕头和厦门的多普勒雷达资料、NCEP再分析等资料,研究2006年5月17日台风"珍珠"的短时特大暴雨特征。多普勒雷达探测表明,17日18～19 h,在台风"珍珠"的核半径附近,正、负径向速度极值区分布不对称,即台风前进方向左侧的径向速度明显地大于右侧,研究表明这种特殊情况是由于冷空气(东北风)侵入所导致的,而且该冷空气侵入主要位于4 km以下的中低层,正是因为冷空气侵入造成强迫抬升,加剧不稳定能量释放,触发强降水产生,冷空气影响后期导致台风迅速减弱。与雷达速度场回波观测到的冷空气侵入相对应,17日18 h NCEP风速资料显示在中低层(约1～3 km)台风中心偏西侧,存在明显的全风速高值区,而除了受冷空气影响部位外,台风前进方向的右侧各层风速仍然大于左侧。利用蓝金模式模拟结果,可进一步证实了在台风前进方向左侧的中低层,东北向气流侵入台风涡旋的事实。通过计算物理量表明,在冷空气侵入区域存在高θse密集锋区,θse密集带从底层向高层、由偏东向偏西、由偏南向偏北方向倾斜,闽南地区的特大暴雨就发生在高θse的密集锋区附近。

With Doppler radar data from Shantou and Xiamen and NCEP/NCAR reanalysis data, characteristics of a short-time super heavy rainstorm on 17 May 2006 caused by Typhoon Chanchu are studied. Doppler radar data indicate that during the period from 18：00 to 19：00 on May 17th, the azimuthal phases of the positive and negative radial wind maximums are asymmetric around the core radius of Typhoon Chancbu, i.e., the radial wind on the left side of the track is anomalously larger than that on the right side. Studies show that it is induced by the intruding of cold air （northeasterly wind） which primarily locates at the mid-lower layers lower than 4 km, and it is because of the intruding cold air that can force the atmosphere to uplift, enhance releases of instability energy and finally trigger the heavy precipitation. Dkuring the late stage of the cold air activity, the typhoon is weakened rapidly. Consistent with the observed intrusion of cold air by radars, the NCEP/NCAR reanalysis wind data also show that there are obvious large scalar wind values at the mid-lower layers （1 - 3 km or so） to the left of typhoon center at 18：00 on May 17th, and in all regions except those affected by the intruding cold air the wind speeds at all the layers on the right side of the track remain larger than those on the left side. Furthermore, the Rankine model results confirm the fact of northeasterly cold air intruding into the typhoon at the mid-lower layers to the left of the track. Calculations also point out that there exists a frontal zone with high θse which tilts from southeast to northwest with height, and the super heavy rainstorm occurring in the south of Fujian province lies just near the front zone.