Vertical velocity structure of marine boundary layer trade wind cumulus clouds

Oceanic trade wind cumulus clouds not only impact the Earth's radiation budget but also affect the boundary layer (BL) structure. Data from the deployment of Atmospheric Radiation Measurements (ARM)'s Mobile Facility at the island of Graciosa in the Azores is used to study the vertical velocity structure of these clouds. The surface fluxes as reported by the European Centre for Medium-Range Weather Forecasting (ECMWF) analysis model were used to characterize the dynamic structure of the BL. Cloud radar data from nine cases totaling to 114 hours and containing 557 cumulus cloud elements are analyzed to report hourly values of mean reflectivity, mean vertical velocity, cloud fraction, and cloud mass flux. The hourly averaged in-cloud vertical velocity was constant (similar to 0.35 m s(-1)) with height, while the average velocity of updrafts and vertically coherent updrafts increased from cloud base to cloud top. The reflectivity did not exhibit any significant changes between all, updraft and coherent updraft samples. The cloud fraction and mass flux showed similar vertical profiles with both having a peak near cloud base. The mass flux contribution of vertically coherent updrafts spanning through the entire cloud layer to the average updraft mass flux was similar to 62%. The hourly values were classified based on the surface convective velocity scale (w*) as reported by the ECMWF model. The cloud fraction near cloud base during hours with w* less than 0.2 m s(-1) was similar to 6% while that during hours with w* greater than 0.6 m s(-1) was similar to 9%. The cloud base mass flux during hours with w* greater than 0.6 m s(-1) was almost double that during hours with w* less than 0.2 m s(-1).