The Evolution of the Clear Air Convective Layer Revealed by Surface-Based Remote Sensors

Abstract

A frequency-modulated, continuous-wave (FM-CW) radar, a high-power, narrow-beam, S-band radar, and an acoustic echo sounder made unique simultaneous observations of the growth and decay of the convective layer near a coastline. The S-band radar scanned the convective field over the vertically pointing radar and echo sounder. Detailed variations in the depth h of the clear air convective layer were observed. Although each sensor observed apparently independent convective features they provided a generally compatible and comprehensive description of the evolution of the convective layer when the individual sensor characteristics are considered. In general, h increased during the morning until about an hour before the maximum surface temperature and decreased slowly in the afternoon. The morning rise rate Δh/Δt increased as the lapse rate of potential temperature γ over the convective layer decreased and was constant during the destruction of each layer having a constant γ. Recent studies propose that Δh/Δt and γ−½ are linearly related by a factor containing the surface heat flux; using the formulation of this factor, the data indicate that the surface heat flux was excessively large. This test suggests that some parametric formulations relating Δh/Δt and γ may require modification. Features of entrainment and the wind field are discussed.