Evaluating the dual role of African dust and water vapor in influencing atmospheric stability across the Caribbean Islands

Abstract

The thermodynamic effect of the Saharan Air Layer (SAL) on convective stability in the Caribbean Basin is investigated through statistical analysis of aerosol optical depth (AOD), water vapor, and convective available potential energy (CAPE) over Barbados, Guadeloupe, Puerto Rico, and the Cayman Islands. This work quantifies the hierarchical controls on atmospheric instability by looking at correlations under dusty and low-dust regimes and percentage changes in CAPE under combined dust-water vapor forcing. The results show that water vapor, which has strong and often significant positive relationships with CAPE, is the primary driver of convection. In contrast, AOD-CAPE correlations are usually insignificant, indicating that dust loading by itself is not a good linear predictor of convective potential. Conversely, dust serves as an important secondary modulator; when combined with water vapor, it continuously reduces CAPE at every site, with average decreases ranging from −0.76 to –18.11%. The largest reductions occur at night in Barbados, highlighting the significance of dust proximity and the absence of daytime thermal forcing. Furthermore, dust acts as a “decoupler”, introducing non-linearity and, in some situations, statistically obscuring the relationship between moisture and CAPE, thereby altering the moisture-convection relationship. These results demonstrate that the convective potential offered by ambient moisture is counteracted by the unidirectional stabilizing effect of Saharan dust on the tropical atmosphere. The findings highlight the necessity of using dust-aware parameterizations in regional climate models and vertically resolved aerosol measurements to enhance forecasts of rainfall, drought, and tropical storm activity throughout the Caribbean.