Estimating radiative forcing efficiency of dust aerosol based on direct satellite observations: case studies over the Sahara and Taklimakan Desert.

The direct radiative forcing efficiency of dust aerosol (DRFE dust) is an important indicator to measure the climate effect of dust. The DRFE dust is determined by the microphysical properties of dust, which vary with dust source regions. However, there are only sparse in situ measurements of them, such as the distribution of the dust aerosol particle size and the complex refractive index in the main dust source regions. Furthermore, recent studies have shown that the non-spherical effect of the dust particle is not negligible. The DRFE dust is often evaluated by estimating given microphysical properties of the dust aerosols in the radiative transfer model (RTM). However, considerable uncertainties exist due to the complex and variable dust properties, including the complex refractive index and the shape of the dust. The DRFE dust over the Taklimakan Desert and Sahara is derived from the satellite observations in this paper. The advantage of the proposed satellite-based method is that there is no need to consider the microphysical properties of the dust aerosols in estimating the DRFE dust. For comparison, the observed DRFE dust is compared with that simulated by the RTM. The differences in the dust microphysical properties in these two regions and their impacts on DRFE dust are analyzed. The DRFE dust derived from the satellite observation is -39.6±10.0 W m -2τ-1 in March 2019 over Tamanrasset in the Sahara and -48.6±13.7 W m -2τ-1 in April 2019 over Kashi in the Taklimakan Desert. According to the analyses of their microphysical properties and optical properties, the dust aerosols from the Taklimakan Desert (Kashi) scatter strongly. The RTM-simulated results (-41.5 to -47.4 W m -2τ-1 over Kashi and - 32.2 to - 44.3 W m -2τ-1 over Tamanrasset) are in good agreement with the results estimated by satellite observations. According to previous studies, the results in this paper are proven to be reasonable and reliable. The results also show that the microphysical properties of the dust can significantly influence the DRFE dust. The satellite-derived results can represent the influence of the dust microphysical properties on the DRFE dust , which can also validate the direct radiative effect of the dust aerosol and the DRFE dust derived from the numerical model more directly. [ABSTRACT FROM AUTHOR]