The Initiation and Development of Rear Inflow Within Two Midlatitude Squall Lines

The formation and evolution of two midlatitude squall lines are analyzed with Doppler radar data. Dual -Doppler analyses and thermodynamic retrievals performed on the squall lines reveal complex squall line evolutions; many features of which have not been observed previously in such systems. Of particular interest to this study was the observed evolution of the strong rear inflows which developed within both squall lines. The storm-relative rear inflows formed and intensified behind (below) the leading edge updrafts of the squall lines, near the center of the high-reflectivity cores. The generation of the rear inflows occurred very early in the life of the squall lines, being visible almost coincident with the formation of the parent systems. The rear inflows were observed to expand toward the rear of the systems with time. 'Bookend'-type vortices and a mesocyclone associated with the stratiform region were found to be significant contributors to the rear inflow strength. The thermodynamic retrievals illustrated that the observed rear inflows were likely forced by hydrostatically induced mid-level low pressure regions in the convective region at the leading edge of the squall lines. These results are consistent with the numerical simulations previously performed by a number of investigators.