Impact of changes in atmospheric conditions in modulating summer dust concentration at Barbados: A back-trajectory analysis

摘要

Atmospheric dust concentrations have been measured continuously since 1965 at Barbados providing one of the longest records of modern atmospheric dust downwind the dust transport route from North Africa toward the Caribbean. The Barbados dust concentration (BDC) record shows a high variability on daily to decadal timescales. This study aims to assess the importance of four processes that have the potential to contribute to the observed day-to-day variability: (1) changes in the transport pathways, (2) changes in atmospheric transport time, (3) changes in the atmospheric dust loadings in the source regions in North Africa, and (4) changes in rainfall. Back-trajectories are calculated for low and high dust days in June (peak month in annual cycle) and analyzed with respect to these four processes. The results show that statistically significant differences exist between low and high BDC days for all four processes. For high BDC days we observe (1) an increase in the number of trajectories (especially at 100 and 150 hPa above the surface) which originated over the North African continent due to differences in the transport pathways, (2) a faster trans-Atlantic transport at the height of the SAL by up to 0.87 days which would mean less dust being removed as a result of dry deposition and less diffusion, (3) increased dust loadings over West Africa and the tropical North Atlantic, and (4) less rainfall in ITCZ region which may have a minor impact of dust loadings due to wet deposition. Our results support the findings of previous studies that changes in dust emission and rainfall impact dust variability over the Atlantic Ocean and the Caribbean. In addition to these two processes, our findings suggest that also changes in the synoptic meteorology over the North Atlantic and varying transport speed can affect BDC variability by modulating dust transport pattern.