Processes Controlling the Structure and Longevity of Two Quasi-Linear Convective Systems Crossing the Southern New England Coast

Abstract

his paper explores the structural evolution and physical processes that explain the modification of two quasi-linear convective systems (QLCSs) that encountered the densely populated New York City?Atlantic coastal region. One QLCS on 31 May 2002 traversed the Atlantic coastal boundary with little change in its intensity, producing widespread severe wind damage across New York City and Long Island. During this event, warm air advection at 925 hPa helped destabilize the layer above this level over the coastal zone, while the marine boundary layer deepened below this level. The 0?3-km line-perpendicular vertical wind shear was relatively strong, which supported ascent along the leading edge of the diabatically generated cold pool. The surface-based convective system became slightly elevated as it moved over the marine waters. In contrast, the 23 July 2002 QLCS decayed upon encountering the Atlantic coastline, despite its coincidence with a surface cold front. The most unstable CAPE values during this decaying event were 400?800 J kg?1 greater than the sustaining 31 May event, though the 0?3-km vertical wind shear was approximately half. Weaker shear likely contributed to limited ascent along the leading edge of the surface based cold pool, and ultimately the demise of the convective line. Sensitivity tests highlight the importance of the relationship between the cold pool and vertical shear during these two events, and illustrate the limited role of the marine layer in modifying the evolution of these two convective systems.