Climatology of Nor'easters and the 30 kPa Jet

Abstract

Waves generated by nor'easters are responsible for a large portion of the coastal damage and erosion that occurs along the Atlantic coast of North America. Large-scale atmospheric circulations, such as the polar jet stream, are the driving forces behind their occurrence. A regional examination of variations in the 30 kPa (the 300 mb constant pressure level in the atmosphere) polar jet stream is conducted for the east coast of North America for 1942-1992. Jet stream variables of wind speed, latitudinal position, geopotential height, 30 kPa temperature, and flow pattern are obtained from 30 kPa mean monthly maps and correlated with the occurrence, intensity, and synoptic type of non-tropical Atlantic coastal storms. Over eastern North America, the polar vortex was most expanded in the early 1940's and the late 1950's and contracted, but less variable, during the remainder of the time period. Geopotential height displayed an inverse relationship with latitude with an overall decline in the 30 kPa height over the fifty-year period. Zonal (west-east) flow patterns of the polar jet were predominant, and upper tropospheric temperatures displayed an overall warming trend while jet stream wind speed remained stable but highly variable. A jet stream/coastal storm analysis revealed that trough flow patterns in the mean pressure field are associated with increased storm frequency. An examination of the storm origin and tracking frequencies displayed a statistically significant relationship between the most potentially dangerous storm types (Bahamas, Florida, and Gulf Lows) and a southerly position and decreased geopotential height of the jet stream. Knowledge of these relationships will improve our ability to understand and predict the impact of various storm-generated wave climates upon the coastal zone.