a Definition of Climatological Seasons and AN Analysis of Air Mass Modification Over the East Coast Using a Year-Round Spatial Synoptic Classification

This paper discusses the application of an automated year-round synoptic classification procedure to define climatological seasons based upon the frequency of occurrence of each seasonal air mass. In addition, the procedure is used to analyze the frequency distribution and character modification of each air mass across the east coast of the United States. The classification is based on seed day identification and discriminant function analysis to assign each day into one of 18 kinds of air masses using more than 43 years of data for each of 14 stations. Unlike arbitrary definitions of seasons which divide a year into four equal periods, the length of winter ranges from about one and one half months in Miami, Florida to more than four months in Portland, Maine based on air mass frequencies. The summer extends more than five months in Florida, while it only lasts three months in Maine. In the mid-Atlantic region (illustrated by Philadelphia), there are two longer seasons and two shorter seasons, of which summer and winter extend four months each, while spring and autumn last slightly more than two months each. In addition, the definition of natural seasons in this study more closely corresponds to phenological data than most previous studies. The determined natural seasons could be useful in environmental planning problems which involve, for example, plant phenology, animal demographics and habitat distributions, and agriculture activities.