期刊名称：Tellus A: Dynamic Meteorology and Oceanography
电子版ISSN：1600-0870
出版年度：1990
卷号：42
期号：1
页码：194-201
DOI：10.3402/tellusa.v42i1.11870
摘要：It is observed from satellite cloud imagery that about 100 neutral vortices per year cross the South American continent between 15-60°S, and almost as many are generated or intensified in the same latitude belt between 30-70°W. There are more cyclogeneses in summer than in winter in contrast to the common idea that winter is the season of maximum extratropical cyclogenesis. The frequency of neutral vortices is higher in the transition seasons than in summer and winter. Neutral vortices move toward the east with a speed of about 20 m/s-1, while the cyclones which develop over the region move south-eastward more slowly with an average speed of 12.5 m/s-1. Vortices crossing the Andes with cyclonic vorticity in excess of 2 × 10-5 s-1 have a 40% probability of producing intense convective systems near the east coast of the continent.
