Empirical TOMS index for dust aerosol: Applications to model validation and source characterization

Abstract

An empirical relation is developed to express the Total Ozone Mapping Spectrometer (TOMS) aerosol index (AI) for the case of dust plumes, as an explicit function of four physical quantities: the single scattering albedo, optical thickness, altitude of the plume and surface pressure. This relation allows sensitivity analysis of the TOMS AI with physical properties, quantitative comparison with dust model results and physical analysis of dust sources, without the necessity of cumbersome radiative calculation. Two applications are presented: (1) the case study of a dust storm over the North Atlantic in March 1988, and (2) the characterization of 13 major dust sources. The first application shows that simulated dust distribution can be quantitatively compared to TOMS AI on a daily basis and over regions where dust is the dominant aerosol. The second application necessitates to further parameterize the relation by replacing the optical thickness and the altitude of the plume by meteorological variables. The advantage is that surface meteorological fields are easily available globally and for decades but the formulation only applies to dust sources. The daily, seasonal and interannual variability of the parameterized index over major dust sources reproduces correctly the variability of the observed TOMS AI. The correlation between these two indices is used to determine the surface characteristics and physical properties of dust aerosol over the sources.