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

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  • 1 Naval Electronics Laboratory Center, San Diego, Calif. 92152
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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 Δht 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 Δht 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 Δht and γ may require modification. Features of entrainment and the wind field are discussed.

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 Δht 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 Δht 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 Δht and γ may require modification. Features of entrainment and the wind field are discussed.

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