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U.K. HiGEM: Simulations of Desert Dust and Biomass Burning Aerosols with a High-Resolution Atmospheric GCM

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  • 1 Environmental Systems Science Centre, University of Reading, Reading, United Kingdom
  • | 2 Met Office, Exeter, United Kingdom
  • | 3 Environmental Systems Science Centre, University of Reading, Reading, United Kingdom
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Abstract

The atmospheric component of the United Kingdom’s new High-resolution Global Environmental Model (HiGEM) has been run with interactive aerosol schemes that include biomass burning and mineral dust. Dust emission, transport, and deposition are parameterized within the model using six particle size divisions, which are treated independently. The biomass is modeled in three nonindependent modes, and emissions are prescribed from an external dataset. The model is shown to produce realistic horizontal and vertical distributions of these aerosols for each season when compared with available satellite- and ground-based observations and with other models. Combined aerosol optical depths off the coast of North Africa exceed 0.5 both in boreal winter, when biomass is the main contributor, and also in summer, when the dust dominates. The model is capable of resolving smaller-scale features, such as dust storms emanating from the Bodélé and Saharan regions of North Africa and the wintertime Bodélé low-level jet. This is illustrated by February and July case studies, in which the diurnal cycles of model variables in relation to dust emission and transport are examined. The top-of-atmosphere annual mean radiative forcing of the dust is calculated and found to be globally quite small but locally very large, exceeding 20 W m−2 over the Sahara, where inclusion of dust aerosol is shown to improve the model radiative balance. This work extends previous aerosol studies by combining complexity with increased global resolution and represents a step toward the next generation of models to investigate aerosol–climate interactions.

* Current affiliation: Met Office, Exeter, United Kingdom

Corresponding author address: Dr. M. J. Woodage, Environmental Systems Science Centre, Harry Pitt Building, 3 Earley Gate, University of Reading, Reading, Berkshire RG6 6AL, United Kingdom. Email: mjw@mail.nerc-essc.ac.uk

Abstract

The atmospheric component of the United Kingdom’s new High-resolution Global Environmental Model (HiGEM) has been run with interactive aerosol schemes that include biomass burning and mineral dust. Dust emission, transport, and deposition are parameterized within the model using six particle size divisions, which are treated independently. The biomass is modeled in three nonindependent modes, and emissions are prescribed from an external dataset. The model is shown to produce realistic horizontal and vertical distributions of these aerosols for each season when compared with available satellite- and ground-based observations and with other models. Combined aerosol optical depths off the coast of North Africa exceed 0.5 both in boreal winter, when biomass is the main contributor, and also in summer, when the dust dominates. The model is capable of resolving smaller-scale features, such as dust storms emanating from the Bodélé and Saharan regions of North Africa and the wintertime Bodélé low-level jet. This is illustrated by February and July case studies, in which the diurnal cycles of model variables in relation to dust emission and transport are examined. The top-of-atmosphere annual mean radiative forcing of the dust is calculated and found to be globally quite small but locally very large, exceeding 20 W m−2 over the Sahara, where inclusion of dust aerosol is shown to improve the model radiative balance. This work extends previous aerosol studies by combining complexity with increased global resolution and represents a step toward the next generation of models to investigate aerosol–climate interactions.

* Current affiliation: Met Office, Exeter, United Kingdom

Corresponding author address: Dr. M. J. Woodage, Environmental Systems Science Centre, Harry Pitt Building, 3 Earley Gate, University of Reading, Reading, Berkshire RG6 6AL, United Kingdom. Email: mjw@mail.nerc-essc.ac.uk

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