THE MOTION AND EROSION OF CONVECTIVE STORMS IN SEVERE VERTICAL WIND SHEAR

Abstract

Well developed thunderstorms were observed by CAPPI-equipped radar to remain upright even in the presence of severe wind shear. Instead of being strongly bent by the shear, parts of the storm appeared to be carried off by the wind, forming extensive plume patterns, which trailed down toward the ground while evaporating. An analysis of the horizontal and vertical development of the plume suggested that its particles had fall speeds ranging from 0.75 to 5 m sec⁻¹ and were thus of precipitation size. The motion of the entire storm system is related to the wind at low levels but only in a general way. Instances where the echo motion differs substantially from the observed winds at all heights are quite common. Vertical motion and storm erosion are used to explain how active cores of large storms remain nearly vertical, almost independently of the wind shear.