An improved Model of Saharan and Asian Dust Aerosols for the Community Radiative Transfer Model

It is well known that the Saharan and Asian deserts are the two largest sources of mineral aerosols on earth and conversely the sources with the largest influence on the terrestrial radiation budget and climate. Naturally it is of outmost importance to parameterise the influence of these particles as accurately as possible when it comes to the calculation of the atmospheric radiative transfer in regions that are afflicted by these aerosols.

Recent studies in the wake of Saharan field campaigns such as SAMUM have identified three factors that lead to considerable inaccuracies in current radiative transfer simulations, including the ones performed using the Community Radiative Transfer Model (CRTM). These factors are variation of particle composition with size, regional variability of aerosol composition as well as size distribution, and finally particle non-sphericity.

A new mineral dust refractive index database has been compiled from the literature and dust regional variability has been studied in order to address these issues. A new set of aerosol coefficients for the CRTM is provided, based on a regional distinction between northern and southern Sahara and western and eastern Asia respectively. In order to efficiently and faithfully recover the refractive index values from the literature tables, novel data mining techniques are employed, specifically optical character recognition.

The new refractive index database is used to calculate a composite refractive index for different aggregate states of pure minerals and the corresponding single scattering properties are then selected from an existing database for spheroidal scatterers, thus addressing the problem of non-sphericity.

In the end, the modified coefficients are validated using atmospheric chemical composition from the Modern-Era-Retrospective-Analysis database, MODIS product and aerosol layer information available from collocated CALIPSO lidar measurements in CRTM calculations over suitable parts of Africa and Asia.