STUDY OF THE MOIST CONVECTIVE BOUNDARY-LAYER STRUCTURE BY BACKSCATTERING LIDAR

Measurements of the structure of the Convective Boundary Layer (CBL) w ere made from the ground and from the ARAT aircraft with a backscatter ing lidar during the preliminary phase of the French project LEANDRE. A numerical model of Mie theory diffusion was used to determine a theo retical profile of the extinction coefficient, as a function of relati ve humidity. Comparisons between theoretical and measured profiles wer e made. Good agreement was found, which confirms that the variation of the extinction coefficient in the CBL is primarily controlled by the relative humidity. This paper also presents a detailed analysis of the small-scale structure of the CBL. The normalized length and number of thermals are estimated. Results are in agreement with previous in-sit u measurements. An analysis of the bidimensional cross-section of the extinction coefficient shows that this coefficient permits one to retr ieve more quantitative information than the range-corrected signal, as the fractions of entrained air and surface-layer air at a given altit ude.