Thermodynamic Variability within the Convective Boundary Layer Due to Horizontal Convective Rolls

Abstract

Data from the Convection and Precipitation/Electrification (CaPE) Experiment conducted during the summer of 1991 are used to examine and quantify the horizontal variability of temperature and moisture within the convective boundary layer (CBL). Potential temperature variations were only about 0.5 K, while variations in water vapor mixing ratio values of 1.5?2.5 g kg?1 were observed throughout the CBL. Using radar, aircraft, and sounding data, it is shown that horizontal convective rolls are the likely cause of these variabilities. The enhanced moisture occurred within the roll updraft regions, thus rolls were transporting moist air from the surface upward. The observed cloud-base heights, obtained from cloud photogrammetry, were produced from the highest moisture values within the roll updraft regions. Since the roll ascending branches contained moisture values that were most representative of the observed cloud-base heights, it is likely that measurements from within the roll updrafts would provide the best estimate of the potential for deep, moist convection.