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

Tian, Lin; Chen, Lin; Zhang, Peng; Bi, Lei

The direct radiative forcing efficiency of dust aerosol (DRFEinline-formuladust) is an important indicator to measure the climate effect of dust. The DRFEinline-formuladust 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 DRFEinline-formuladust 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 DRFEinline-formuladust 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 DRFEinline-formuladust. For comparison, the observed DRFEinline-formuladust is compared with that simulated by the RTM. The differences in the dust microphysical properties in these two regions and their impacts on DRFEinline-formuladust are analyzed.

The DRFEinline-formuladust derived from the satellite observation is inline-formula M9inlinescrollmathml - normal 39.6 ± normal 10.0 64pt10ptsvg-formulamathimg8bd29cee93e761c11b5443b81869f690 acp-21-11669-2021-ie00001.svg64pt10ptacp-21-11669-2021-ie00001.png  W minline-formula M10inlinescrollmathml - normal 2 italic τ - normal 1 28pt13ptsvg-formulamathimgfb266fc636c90b55e4d840f7cf79a736 acp-21-11669-2021-ie00002.svg28pt13ptacp-21-11669-2021-ie00002.png in March 2019 over Tamanrasset in the Sahara and inline-formula M11inlinescrollmathml - normal 48.6 ± normal 13.7 64pt10ptsvg-formulamathimg1b23cebf5b9e30bf64f9237797c734bb acp-21-11669-2021-ie00003.svg64pt10ptacp-21-11669-2021-ie00003.png  W minline-formula M12inlinescrollmathml - normal 2 italic τ - normal 1 28pt13ptsvg-formulamathimg202021a76ba8f81ff1b65beb4b42dea7 acp-21-11669-2021-ie00004.svg28pt13ptacp-21-11669-2021-ie00004.png 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 (inline-formula−41.5 to inline-formula−47.4 W minline-formula M15inlinescrollmathml - normal 2 italic τ - normal 1 28pt13ptsvg-formulamathimgc8258f70d0887afb1c38d53564a94f11 acp-21-11669-2021-ie00005.svg28pt13ptacp-21-11669-2021-ie00005.png over Kashi and inline-formula−32.2 to inline-formula−44.3 W minline-formula M18inlinescrollmathml - normal 2 italic τ - normal 1 28pt13ptsvg-formulamathimg0a3a36dda70656973161cb8fea49dce3 acp-21-11669-2021-ie00006.svg28pt13ptacp-21-11669-2021-ie00006.png 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 DRFEinline-formuladust. The satellite-derived results can represent the influence of the dust microphysical properties on the DRFEinline-formuladust, which can also validate the direct radiative effect of the dust aerosol and the DRFEinline-formuladust derived from the numerical model more directly.

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Tian, Lin / Chen, Lin / Zhang, Peng / et al: Estimating radiative forcing efficiency of dust aerosol based on direct satellite observations: case studies over the Sahara and Taklimakan Desert. 2021. Copernicus Publications.

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