The Humidity and Temperature Sensitivity of Clear-Air Radars in the Convective Boundary Layer

Abstract

Abstract A top-down/bottom-up diffusion Model is used to evaluate the relative contributions of humidity temperature, and their cross correlation to the radar refractive index structure function paramer Cn2 in the cloud-free, convective planetary boundary layer (PBL). Profiles of Cn2 can be measured continuously in the clear air with Doppler radars. Extraction of information about PBL dynamical parameters is more straightforward if Cn2 is dominated by either moisture (Cq2) or temperature (CT2). In the lower part of the PBL the surface Bowen ratio β0 determines this dominance. In the upper part of the PBL the inversion Bowen ratio β1 is the primary determining factor. The model suggests that humidity accounts for at least 75% of Cn2 over tropical and midlatitude oceans. Polar oceans, where β0 often exceeds 0.5, may not be dominated by either temperature or moisture. Over land β0 can easily vary from 0.1 to 10. Geographical regions with β0 5 wil...