Analysis of the Structure of Precipitation Patterns in New England

Abstract

The studies presented here were undertaken to provide a specific and quantitative description of the precipitation patterns in New England storms. Basic data were quantitative radar observations and detailed raingage records. Nine storms covering a wide range of synoptic and seasonal situations were subjected to systematic analysis. Also the general shape and configuration of the mesoscale rain areas in seventeen fully developed cyclones were observed. The precipitation patterns, which at first glance appeared very dissimilar, out to be composed of subsynoptic-scale precipitation areas with rather clearly definable characteristics and behavior. Four distinct scales of precipitation areas have been recognized and described: synoptic arms which are larger that 10⁴ km² and have a lifetime of one or several days; large mesoscale areas which range from 10³–10⁴ km² and last several hours; mesoscale areas which cover 100–400 km² and last about an hour; and cells which are roughly 10 km² and often last only a few minutes, rarely as long as half an hour. In the cases which were analyzed every precipitation area of any of these scales contained one or several of each of the smaller sized precipitation areas. The motions and relative intensifies of precipitation areas of the various scales also a consistent pattern. The vertical location and depth of the layer containing cells varied greatly from one storm to another, but remained about the same within any particular storm. The consistent occurrence of subsynoptic-scale rain areas with similar characteristics and behavior in a variety of precipitation patterns provides a means for describing the distribution of precipitation in any storm in a parameterized manner and also permits realistic modeling of storms for meteorological and hydrological studies.