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- Title
Dust size parameterization in RegCM4: Impact on aerosol burden and radiative forcing.
- Authors
Tsikerdekis, Athanasios; Zanis, Prodromos; Steiner, Allison L.; Solmon, Fabien; Amiridis, Vassilis; Marinou, Eleni; Katragkou, Eleni; Karacostas, Theodoros; Foret, Gilles
- Abstract
We investigate the sensitivity of two dust parameterizations of the regional climate model RegCM4 for the period 2007-2014 over the Sahara and the Mediterranean. We apply two discretization methods of the dust size distribution keeping the total mass constant: 1) the default RegCM4 4-bin approach, where the size range of each bin is calculated using an equal, logarithmic separation of the total size range of dust, using the diameter of dust particles and 2) a newly implemented 12-bin approach with each bin defined according to an isogradient method where the size ranges are dependent on the dry deposition velocity of dust particles. Increasing the number of transported dust size bins theoretically improves the representation of the physical properties of dust particles within the same size bin. Thus, more size bins minimize the error and improve the simulation of atmospheric processes. The radiative effects of dust over the area are discussed and evaluated with the CALIPSO Dust Optical Depth (DOD). This study is among the first studies evaluating the vertical profile of simulated dust with a pure dust product. Reanalysis winds from ERA-interim and the total precipitation flux from the observational gridded database CRU are used to evaluate and explain the discrepancies between model and observations. The new dust binning approach increases the dust column burden by 4 % and 3 % for fine and coarse particles respectively, which increases DOD by 10 % over the desert and the Mediterranean. Consequently, negative shortwave RF is enhanced by more than 10 % at the top of the atmosphere and by 1 % to 5 % on the surface. Positive longwave RF locally increases by more than 0.1 W m−2 in a large portion of the Sahara desert, the northern part of the Arabian peninsula and the Middle East. The 4-bin isolog method is to some extent numerically efficient, nevertheless our work highlights that the simplified representation of the 4-bin approach underestimates the dust optical depth and the radiative forcing, a fact that should be taking into account by future researches that study the same region.
- Subjects
ATMOSPHERIC aerosols; RADIATIVE forcing; ATMOSPHERIC models; DUST; SENSITIVITY analysis; PARAMETERIZATION; DISCRETIZATION methods
- Publication
Atmospheric Chemistry & Physics Discussions, 2016, p1
- ISSN
1680-7367
- Publication type
Article
- DOI
10.5194/acp-2016-434