An Observation-Based Study of the Sensitivity of Dust Aerosol Net Direct Radiative Effects to the Physical and Optical Properties of Dust

Dust aerosols play an important role in the radiative energy budget of Earth-Atmospheric system. They participate in Earth’s energy budget directly by absorbing and scattering radiation, which is so called direct radiative effect (DRE).

Many previous studies have focused on studying the DRE of dust in the shortwave (SW) domain. However, dust aerosols are large enough in size to have significant longwave(LW) DRE. Recently, dust longwave(LW) DRE have obtained more and more interest from scientists, but the DRE of dust aerosols remains uncertain in magnitude and even sign in recent assessments. These uncertainties are mainly in the microphysical and optical properties of dust.

The first objective of this research is to perform an observation-based sensitivity study of dust SW, LW and net DRE to dust size distribution, shape and refractive index. Different sets of dust size distribution, shape and refractive index are used in this research to compute the optical properties. We use the Rapid Radiative Transfer Model (RRTM) driven by atmospheric profiles and aerosol extinction profiles derived from CALIPSO in CERES, CALIPSO, CloudSat and MODIS merged product (CCCM) to compute both SW and LW forcing efficiency. Then the sensitivity of dust DRE to those properties will be analyzed. In addition, an optimal combination of dust size distribution and refractive index, which provides good agreement with CERES observation in both outgoing longwave radiation and upward shortwave radiation, will be found.

The second objective of this research is to evaluate dust net DRE in North Atlantic region by using the optimal combination mentioned previously.