Determining Cyclone Frequencies Using Equal-Area Circles

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Abstract
This paper examines recent cyclone frequencies with a methodology that incorporates the use of 5° latitude equal-area circles located in a grid for a region centered from 25° to 70°N and 60° to 140°W. Cyclones were counted in 82 equal-area circles for the period 1950–93 over North America. The grid of equal-area circles eliminated two related problems associated with conventional grid systems, area-inequality, and area-normalization, and allows for comparison of frequency counts among circles. An analysis of winter cyclones among four north-to-south circles on a meridian indicated latitudinal variability in year-to-year raw cyclone counts. Correlation coefficients developed from relating winter cyclone counts from one circle to another were less than ±0.29, implying that the location of the axis of maximum winter cyclone frequency varies annually. Results revealed that winter and spring had the greatest number of cyclones and the southernmost position of the axis of maximum frequency. Summer and ... Abstract This paper examines recent cyclone frequencies with a methodology that incorporates the use of 5° latitude equal-area circles located in a grid for a region centered from 25° to 70°N and 60° to 140°W. Cyclones were counted in 82 equal-area circles for the period 1950–93 over North America. The grid of equal-area circles eliminated two related problems associated with conventional grid systems, area-inequality, and area-normalization, and allows for comparison of frequency counts among circles. An analysis of winter cyclones among four north-to-south circles on a meridian indicated latitudinal variability in year-to-year raw cyclone counts. Correlation coefficients developed from relating winter cyclone counts from one circle to another were less than ±0.29, implying that the location of the axis of maximum winter cyclone frequency varies annually. Results revealed that winter and spring had the greatest number of cyclones and the southernmost position of the axis of maximum frequency. Summer and ...

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