The Climatology of Cyclones and Anticyclones over North America and Surrounding Ocean Environs for January and July, 1950–77

The climatology. of cyclones and anticyclones is studied using a 2° latitude/longitude grid spanning North America and surrounding ocean environs for January and July 1950–77. In addition to determining total area statistics, areas distributions of cyclone/anticyclone events, genesis, decay and relative variability are analyzed, and preferred propagation tracks are determined. Further, the temporal variability of cyclone and anticyclone occurrences is examined. In general, cyclones and anticyclones are more numerous, more intense, and displaced farther south in January than in July. Cyclogenesis occurs most frequently along the cast coast of the United States and in the lee of the Rocky Mountains, while anticyclones tend to originate in northern Canada and in the Great Plains region of the United States in January and in southwestern Canada in July. Cyclones generally propagate to the east and northeast from genetic regions, while anticyclones propagate to the east and southeast after forming. The Rocky Mountains are a barrier to cyclones penetrating eastward from the Pacific, while anticyclones tend to dissipate along the eastern coast of the United States. Although year-to-year fluctuations are quite prominent, the total number of both cyclones and anticyclones has decreased significantly over the 28-year period.