Barbados Aerosol Cloud Experiment—BACEX

The purpose of the Barbados Aerosol Cloud Experiment (BACEX), carried out from 15 March to 15 April 2010, was to observe the time evolution of the cloud and precipitation characteristics of individual oceanic cumulus clouds and to develop statistics on aerosol, cloud, and precipitation under varying aerosol conditions. The principal observing platform for the experiment was the Cooperative Institute for Remotely Piloted Aircraft Studies (CIRPAS) Twin Otter (TO) that was equipped with aerosol, cloud, and precipitation probes and standard meteorological instrumentation for observing mean and turbulent thermodynamic and wind structures. The highlight of the TO observing package was an upward facing FMCW Doppler 95 GHz radar (designed and fabricated by ProSensing). The use of the FMCW radar, which has a dead zone of less than 50 m, allows for radar observation in close proximity to the in situ probe measurements. The Doppler spectra from the radar proved to be rich in structure that will help deconvolve the contributions to the radar returns from both cloud and rain. The aircraft was used to characterize the structure of shallow to moderately deep (cloud tops less than 3 km) and mostly precipitating marine cumulus clouds. The aircraft observations were made just upstream from a point on the eastern shore of Barbados (Ragged Point) where surface aerosol measurements (Joe Prospero, University of Miami) were made along with aerosol characterizations from a NASA AERONET tracking sun photometer for aerosol optical depth (AOD) and a micro-pulse LIDAR. Routine rawindsonde observations made daily from the island (by Barbados Meteorological Service) and observations from an S-Band radar (by Caribbean Meteorological Organization) on Barbados were collected in support of BACEX. The aircraft observations also were made in conjunction with initial lidar, radar, and ceilometer observations from a surface sight near Ragged Point that were made as part of the Aerosols, Clouds, Precipitation and Climate: Barbados Field Study under development by the Max Planck Institute for Meteorology and that will be in place for the next two years. . This presentation will include an overview of BACEX and a discussion of initial results. The Twin Otter was able to sample many clouds in various phases of growth during BACEX. Precipitation varied from light to heavy with the convection showing substantial meso-scale organization on several of the flights. Rapidly dissipating clouds (life-times of less than 10-15 minutes) were probed on several occasions by cloud penetrations starting from cloud top and working downward with time. The time evolution of these strongly precipitating clouds will be documented and the relative role of precipitation and evaporation (through entrainment) in explaining these results will be discussed. The principal variability in the background aerosols observed during these flights was associated with African dust above the boundary layer. On two days when convection was completely suppressed, an African dust event associated with near record AODs for Barbados during this time of the year was observed. The vertical structure of the aerosols and the boundary layer observed during these cases will be documented and the reasons for the suppressed convection will be discussed.