Climatology of 500 mb cyclones and anticyclones, 1950-85

Abstract

The 500 mb cyclones are found primarily at middle and high latitudes, while anticyclones are observed most frequently over the subtropics. Cyclone frequency increases over the northern oceanic regions during summer, while anticyclone frequency increases throughout the subtropics during summer, especially over southwestern North America. The correlation between 500 mb cyclone frequencies and 300 mb westerly momentum transports is also investigated, revealing that 500 mb cyclones may be associated with the convergence of westerly momentum into the 300 mb westerly jet. Finally, temporal trends in the frequencies indicate that 500 mb cyclone frequencies declined from 1950 through 1970 but increased from 1971 through 1985, while 500 mb anticyclone frequencies declined from 1950 through 1985. -from Authors