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ABSTRACT The assumption is made that mean monthly rainfall totals for a location are vector quantities, magnitude being the amount of rain, and direction being the month expressed in units of arc. When monthly figures are added vectorially, the resultant can be used to compute a Seasonality Index, which is the ratio of the magnitude of the resultant to the mean annual rainfall total. The period of seasonal concentration is given by the direction of the resultant. Data from several hundred stations in the United States and adjacent regions are analyzed by this method, and maps of Seasonality Index and Period of Seasonal Concentration are presented.
Charles G. Markham (Tue,) studied this question.