An Investigation of Dust Impacts on Local Convective Processes over Puerto Rico

This work aims to study the impacts of Saharan dust on tropical island convective processes and therefore local storm production on the Caribbean island of Puerto Rico. Saharan dust can modify atmospheric conditions and mitigate precipitation in the local environment by creating a drier environment and via the suppression of cloud droplet growth. As a result, local island processes which fuel convective rain events compete with the warm rain mitigation effects of the dust to produce storms. Robust measurement of local aerosol particle size distribution (PSD) is vital to improving the understanding intense rain events. Herein we employed a Light Optical Aerosol Counter (LOAC) to attain aerosol PSD and typology during an observational campaign in western Puerto Rico that occurred from 20-27 June 2019, during which two Saharan dust events occurred. The LOAC data was cross referenced with PSD calculations attained from the NASA Aerosol Robotic Network (AERONET), and backscatter intensity from a CL51 Ceilometer located in western Puerto Rico. Analysis of the data suggests that the dry Saharan Air Layer (SAL) caused convective capping and reduced the available water vapor while the hydrophobic Saharan dust particles suppressed droplet growth. The summation of these effects inhibited storms from occurring in the highly convective environment. The LOAC attained PSD was ingested into the high-resolution cloud resolving Regional Atmospheric Modeling System (RAMS) to further zoom in on aerosol impacts on precipitation. Results from the numerical experiments support the campaign findings, with rainfall suppression during dust ingestion attributed to drier air in the low to mid troposphere (up to 4 km), and reduced precipitable water by as much as 21%.