Near-Tropopause Vertical Motion within the Trailing Stratiform Region of a Midlatitude Squall Line

Abstract

Abstract Rawinsonde observations have been used to determine the flow structure in the vicinity of the tropopause atop the trailing stratiform precipitation region of an intense midlatitude squall line. Computations of vertical motion using the kinematic and thermodynamic methods show (i) upward motion in the mid- to upper troposphere within the stratiform cloud and (ii) downward motion in a thin layer 2–3 km deep centered near the tropopause at cloud top. The latter feature, which has received little attention and explanation, has recently been reported to exist above stratiform rain areas in the tropics, as measured directly by a wind profiler on the tropical western Pacific island Pohnpei. The thin layer of sinking at the top of the trailing stratiform region occurs along the sloping upper cloud boundary and is associated with downward-sloping isentropes in the lower stratosphere to the rear of the convective line. The deformation of the isentropes is associated with an upward bulging of the tropopause...