10 July 2014

Dust Increases Low Cloud Cover


Mineral dust interacts with the local and remote climate in a variety of ways, and has been linked to the modification of cloud properties and precipitation. Dust effectively absorbs and scatters incoming shortwave radiation and outgoing terrestrial longwave radiation. A team of scientists, including a Department of Energy researcher at Pacific Northwest National Laboratory, used oceanic and atmospheric output from a century-length simulation by the Community Earth System Model (CESM) to explore statistical relationships between North African dust, clouds and circulation. They found a surprising increase in cloud cover when more dust blows off the west coast of Africa. The simulation analyses strongly suggest that African dust and low cloud cover over the eastern North Atlantic are dynamically linked, and that transported African dust enhances lower tropospheric cloud cover over the open ocean via a semi-direct mechanism. The summertime transport of dust in the lower troposphere over the open ocean in CESM is consistent with observational studies that have investigated the mechanisms controlling the vertical structure of dust near the Saharan Planetary Boundary Layer. Enhanced lower tropospheric cloud growth due to increased dust transport could further decrease the likelihood of hurricane formation in the Atlantic due to reduced sea surface temperature, which has the potential to strongly impact the economies of Caribbean island nations, Mexico, and the eastern United States.

Michael J DeFlorio
University of California San Diego
DeFlorio, MJ, SJ Ghan, B Singh, AJ Miller, BR Cayan, LM Russell, and RC Somerville.  2014.  "Semidirect Dynamical and Radiative Effect of North Africa Dust Transport on Lower Tropospheric Clouds Over the Subtropical North Atlantic in CESM 1.0."  Journal of Geophysical Research - Atmospheres, doi:10.1002/2013JD020997.