Increase in Summertime Dust Loading over the Sub-Tropical North Atlantic Ocean from MODIS during 2002–2012

The Saharan desert in northern Africa is a large source of atmospheric dust aerosol.  Dust plays an important role in the Earth system due to its impacts with radiation, interactions with clouds, and nutrient fertilization of the ecosystem.  We have identified a region of the sub-tropical North Atlantic that is experiencing an increasing aerosol load from 2002 to 2012 as seen by MODIS AOD trends (> 0.02 per decade).  In the present work we use satellite observations (MODIS) and atmospheric reanalysis (MERRA) monthly mean data sets to explore the cause of this trend and point towards an increase in summertime (June, July, and August; JJA) dust loading.  Using a parameterization from Kaufman et al. (2005) we estimate the dust optical depth, dust mass, and dust mass flux during the period of consideration.  Seasonal trend analysis reveals increasing trends in dust optical depth and mass in the sub-tropical North Atlantic during JJA.  This results from an increase in dust convergence from mass flux estimates.  We explore a variety of mechanisms that may be linked to the dust increases, and find a strengthening Saharan Heat Low and cotemporaneous strengthening and northward shift of the African Easterly Jet likely acting in concert to increase JJA dust loading and export from the Sahara and to influence a more northerly transport route across the North Atlantic.  The change in dust load and distribution across the sub-tropical North Atlantic is expected to have impacts on radiative forcing of the atmosphere and sea-surface, cloud formation and evolution, and nutrient availability in the ocean from dust deposition.