THE FREQUENCY OF CYCLONES AND ANTICYCLONES IN RELATION TO THE MEAN CIRCULATION

Abstract

Monthly frequencies of occurrence and genesis of migratory cyclones and anticyclones at sea level in the Northern Hemisphere during the period covered by the original Historical Map Series are averaged by 5 deg lat zones. The mean meridional distribution and annual march of these frequencies are summarized by means of four time-latitude sections. These sections are related to a corresponding diagram for the normal zonal circulation of the Northern Hemisphere at the 700-mb level. Additional statistics are presented on the average speed and life span of pressure centers and on the relative frequencies of lows, highs, cyclogenesis, and anticyclogenesis.