<title>Optical characteristics of desert dust</title>

Abstract

We have been conducting research aimed at enabling prediction of desert optical environments from meteorological and satellite observations. To this end we have been collecting aerosol size distributions, visibility and meteorological data continuously for the past year at 2 sites in the Mojave Desert of California. Optical properties of dust are calculated from these data for a great variety of meteorological conditions. The concentration of dust particles is strongly dependent on wind speed for speeds greater than a threshold (7 m/s at Edwards and 15 m/s at China Lake). For individual wind episodes there is a clear relationship between wind speed and dust mass. However, that relationship changes from event to event leading to noisy summary plots; thus, indicating that other factors, such as dust sources, also influence dust loading. The HYPACT program is used to map out the sources, concentration and flow of dust. HYPACT is a pollution transport program that uses RAMS meteorological code output for input. HYPACT can calculate concentration forward in time from an assumed emission source or backward in time from an observation site. This facilitates the location of dust sources and the calculation of dust concentrations along air streams. Once dust concentrations are known and assuming the particle size distributions are the same as at the measurement sites knowledge of IR extinction is no longer confined to just the measurement sites.