Fifteen-Year Trend in African Dust Outbreaks across the U.S. Caribbean

Although several field campaigns have been conducted to have a better understanding of optical, chemical and physical properties of the African Mineral dust across the Eastern Caribbean; there are still fundamental questions unanswered regarding frequency and magnitude of dust outbreaks particularly in the vicinity of Puerto Rico and the US Virgin Islands (US Caribbean). The goal of this study was to identify the trends in frequency and magnitude of African Dust Days (ADD) across the US Caribbean since most analyses have been performed well south in the vicinity of Barbados. Even more important, and has not been done before, the North Africa Dipole Intensity (NAFDI) index was correlated with the US Caribbean dustiness as a potential predictor of enhanced activity.

The daily area-averaged Aerosol Optical Depth (AOD) retrieved from the MODerate Resolution Imaging Spectroradiometer (MODIS-Aqua) between latitudes 13° and 23° North and longitudes 61° and 71° West combined with the Extinction Ångström Exponent (EAE) retrieved from the AErosol RObotic NETwork (AERONET) at Cape San Juan (CSJ), Fajardo, Puerto Rico and La Parguera (LP), Lajas, Puerto Rico were analyzed to identify ADD. These days were identified using the 75th (D75) percentile within the log-normal distribution of AOD MODIS-retrieved (AOD of 0.23) combined with EAE values below 0.2 at CSJ and LP. Having the number of ADD per season, the trends in frequency and magnitude were calculated using the Rate of Change (ROC) with time.

Although there were no changes observed in the frequency or magnitude of ADD across the US Caribbean between 2003 and 2018, the highest frequency of ADD during the months of July was correlated with positive values of the NAFDI index. Positive values of the NAFDI index indicate dust source intensification over central-south Argelia and transport toward the Subtropical Atlantic.