UC San Diego

Mineral dust contributes significantly to the regional aerosol mass of the Sonoran Desert where wind-driven dust storms are commonplace. These suspended dust particles scatter and absorb solar and terrestrial radiation transmitted through the atmosphere. Here, we derive the source dependent optical properties of airborne dust in the arid regions adjacent to the Salton Sea. In effort to quantify the dust direct radiative effect, surface mineral abundance from the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) mission are utilized to derive bulk refractive indices ($N=n - ik$), extinction coefficients ($\beta_{ext}$), single scatter albedo ($SSA$), and asymmetry parameter ($g$) of airborne dust (size range 0.1 – 100 $\mu$m). Dust optical properties are input into the Rapid Radiative Transfer Model (RRTM) to simulate dust influence on the atmosphere/Earth radiation budget. Following implementation of these optical properties, the model output is used to calculate atmospheric radiative fluxes ($\Delta F$). Differences in dust iron content is found to be responsible for regional variability in $k$ and $SSA$. Simulations of radiation at the surface, within the atmosphere, and top-of-atmosphere (TOA) reveal the dust shortwave and longwave direct radiative effect (DRE). Estimates of DRE at the TOA range from -26.5 to -5.59 $\mathrm{Wm^{-2}}$ among three emission sources, where greater iron content is associated with warming. Results indicate distinct radiative effects of bulk dust that is dependent on modeled mineral composition as a function of soil source mineralogy.