Determination of climatological seasons for the East Coast of the US using an air mass-based classification

This paper discusses the application of a year-round synoptic classification procedure to define climatological seasons based upon the frequency occurrence of seasonal air masses. The classification is developed through air mass 'seed day' identification and discriminant function analysis, and assigns each day to 1 of 18 air mass types for each of 14 stations along the East Coast of the United States. Unlike the 'astronomical' definition of seasons, which divides a year into 4 equal periods, the length of winter ranges from about 1 1/2 mo in Miami, Florida to more than 4 mo in Portland, Maine as determined by air mass frequencies. The summer extends more than 5 mo in Florida, while it only lasts 3 mo in Maine. In the mid-Atlantic region, there are 2 longer seasons (summer and winter; about 4 mo each) and 2 shorter seasons (spring and fall; about 2 mo each). The seasonal definition proposed here more closely corresponds to phenological responses than do traditional definitions. The information can be applied to numerous environmental assessment problems, including animal demographics and habitat distributions, plant phenology and subsequent pollen release, migration and hibernation pat terns, human health and psychological responses to climate, and agricultural planning activities.