Regionalization of Northeast US moisture conditions: analysis of synoptic-scale atmospheric drivers

Abstract

Previous investigations have documented relationships between global-scale forcings and Northeast United States moisture conditions, yet the physical pathways from global-scale forcing to sub-regional moisture deficit or surplus are not well understood. This research uses eigenvector-based regionalization to confirm the existence of sub-regional moisture environments within the Northeast. Synoptic classification is used to derive daily weather types that impact these moisture environments, and evaluate the relationship between global and synoptic scales. The Palmer Drought Severity Index (PDSI) regionalization identifies 3 sub-regions across the Northeast with homogeneous moisture conditions including New England, the Eastern Great Lakes, and Mid-Atlantic Regions. All 3 regions’ PDSI conditions are predominantly associated with variations in precipitation, rather than thermal characteristics. The frequency of key precipitation-associated synoptic types can inform PDSI variability in the regions, where drier conditions are observed during growing seasons with a reduced frequency of precipitation-inducing synoptic types and an enhanced frequency of dry synoptic types. Variations in the frequencies of these synoptic types are partially explained by the phase of the various teleconnection patterns. In the case of the New England region, 14% of the variance in PDSI is explained by the frequency of synoptic type D2, and 12% of the variance in D2 is explained by variations in the Summer Atmospheric Drought Index. The New England region became significantly wetter (positive PDSI) from 1950 to 2016. This study suggests a partial cause of this trend is the increased and decreased frequencies of wet and dry synoptic types, respectively, both related to the phase of the Summer Atmospheric Drought Index.