A Field Campaign for Tropical Convective Precipitation During Saharan Dust Season

This work is motivated by the necessity to understand convective clouds and precipitation in the aerosol rich environment of the Caribbean. Between June and August, high concentrations of mineral aerosols from the African Sahara (Saharan Dust, SD) travel westward and blanket the Caribbean in dust. It is suspected that this dust suppresses precipitation during the summer months and may lead to cooling of the Atlantic Ocean and suppression of tropical storm activity for intense SD seasons. To better understand the role of SD in Caribbean precipitation and convection, a data retrieval campaign was coordinated and executed between June and July 2014 on the western side of the island of Puerto Rico (Mayagüez; 18.2138N, 67.1310W) using a suite of on-site and remote sensors including radiosondes, sunphotometers from the NASA maintained Aerosol Robotic Network (AERONET), a 3-channel lidar system, and a ceilometer operated simultaneously, and analyzed in tandem with National Weather Service (NWS) observations. The data was used to investigate and categorize the boundary layer and convective cloud structure during dry and wet days for varied dust intensities over western Puerto Rico during the peak of the SD season. Analysis of the data shows that: 1) the regional wind shear factor was favorable for convective activity, 2) total accumulated daily rainfall for the period ranged from 0-140 mm with the heaviest precipitation concentrated on the western side of the island with clouds generally developing at a base between 1.5 and 2.5 km, 3) dust was captured via lidar up to 4 km with heavy dust shielding clouds and producing less precipitation over Mayagüez than light dust by as much as 50%, 4) the planetary boundary layer (PBL) height did not extend beyond 5 km with atmospheric stability extending until early afternoon hours, 5) sea-breeze intensity may reach 9 m/s with 2.5 km height, impacting precipitation formation in afternoon storms when converging with easterly convective clouds, and 6) Skew-T plots produced using western campaign data had similar thermal boundary layer profiles with higher moisture when compared with data from NWS launches about 100 km away at the eastern end of the island.