陆地上爆发性温带气旋的暖锋后弯结构分析

温带气旋的暖锋后弯是20世纪80年代末从北大西洋爆发性气旋现场科学试验中发现的一个重要科学成果, 修正了 经典温带锋面气旋模式中锢囚锋的概念。在地球同步卫星云图上, 经常可以观测到欧亚大陆的气旋云系也存在与暖锋后弯 非常类似的演变过程。利用常规的高空、地面观测, NCEP的1°×1°再分析场和FY-2E 水汽图像等资料, 通过分析2012年5 月11-14日一次蒙古气旋强烈发展的结构特征, 揭示了在内陆地区温带气旋发展过程中若暖锋锋区增强而冷锋锋区减弱, 则 该类气旋也存在暖锋后弯和暖核被隔离的事实。分析结果还表明该类蒙古气旋中暖核强度虽不如海洋爆发性气旋, 但其厚 度可伸展到600hPa,在对流层低层850hPa低压中心附近不仅有暖核, 而且存在与暖核近乎重合的干中心, 但干暖中心与气 旋中心并不重合。另外, 单站探空及垂直剖面的分析显示, 在后弯的暖锋锋区附近存在强的湿上升运动, 干暖核内以干空气 和下沉运动为主, 在边界层内后弯暖锋锋区比冷锋锋区强;在冷锋后部的干输送带中对流层中高层锋区明显, 且总体上相对 湿度较小、上升运动微弱, 最显着的干区位于锋区上方下沉的暖空气中。

Analysis of the back-bent warm front structure associated with an explosive extratropical cyclone over land

The back-hent warm front of extratropical cyclone was a significant achievement as done in the field experiment on rapidly intensifying cyclones over the Atlantic Occan(ERICA) in the late 1980s because it modified the occluded front concept in the classical Norwegian cyclone model. This evolution process was found in cyclonic cloud systems over the Eurasian continent as observed from geosynchronous satellite images. Therefore,the frontal structure and feature of the Mongolian cyclone that occurred on 11-14 May 2012 was analyzed using conventional ohservations,the NCEP 10 x 10 reanalysis data and water vapor images from FY-2E. It is shown that the back-hent warm front and warm seclusion existed in the extratropical cyclone over land,but its warm core,which extended up to the 600 hPa level, was weaker than that of the marine cyclone. In addition a dry center at the 850 hPa level was found near the warm core and it partly coincided with the low center. It is also found that the moist air ascended near the back-bent warm front zone while the dry air descended within the warm,dry center. And the potential temperature gradient in the back-bent warm front was stronger than that in the cold front in the boundary layer. In the dry conveyor belt,the front zone located evidently in the middle-upper troposphere with low relativity humidity and slowly up-ward vertical velocity in general. The driest air was situated above the front zone with the warm air descending.