A recently developed continental-scale air mass-based classification is used to identify the spatial occurrences of 6 air masses (dry polar, dry temperate, dry tropical, moist polar, moist temperate, and moist tropical) in the eastern United States for summer from 1961 to 1990. This procedure, the spatial synoptic classification (SSC), is based on 'seed' day identification of synoptic events and discriminant analysis to group days together which are within the same air mass type. Thus, the evaluation of the frequency and modification of air masses across a large region is possible. Using the SSC, maps of air mass frequencies and afternoon temperatures and dew points are developed. Rates of modification are determined as each air mass traverses the region. As an example of the environmental applicability of the SSC, the impact of climate upon human mortality is analyzed at 3 climatically different locations (New Orleans, LA; Memphis, TN; and Chicago, IL). Results show how the day-to-day mortality fluctuations are sensitive to air mass type. A particular air mass which is associated with distinctly high mortality is identified for Memphis and Chicago; no such air mass is apparent for New Orleans, where the weather/mortality signal is very weak.

This paper discusses the application of a year-round synoptic classification procedure to define climatolog~cal seasons based upon the frequency occuiience of seasonal air masses The classification is developed through air inass 'seed day identification and discriminant function analysis, and assigns each day to 1 of 18 ail mass types for each of 14 stations along the East Coast of the United States Unlike the 'astronomical definitlon of seasons, which divides a year into 4 equal p e i~o d s , the length of wlnter ranges fiom about 1'4 mo in Mlami, Florida to more than 4 mo in Portland, hdaine as determined by air mass frequencies The suminer extends more than 5 mo in Flonda, whlle it only lasts 3 mo in Maine In the mld-Atlantic region, there ale 2 longer seasons (summer and wlntei, about 4 mo edch) and 2 shorter seasons (spnny and fall, about 2 mo each) The seasonal definitlon proposed here more closely corresponds to phenological responses than do t r a d~t~o n a l def~nitions The lnforination can be applied to numerous environmentdl assessment problems, including animal demographics and habitat distnbutions, plant phenology and subsequent pollen release, m~gration and hibernation patterns, human health and psychological iesponses to climate, and agncultural p l a n n~n g activities