The role of refractive indices in measuring mineral dust with high-spectral resolution infrared satellite sounders: Application to the Gobi Desert

Abstract. Mineral dust significantly influences the Earth's climate system by affecting the Earth's radiative balance through the absorption and scattering of solar and terrestrial radiation. Understanding the physico-chemical properties of dust in the longwave region of the electromagnetic spectrum is crucial for a more accurate estimation of the radiative budget. The complex refractive index (CRI) of dust in the infrared (IR) is a key parameter for mineral dust characterization from satellite remote sensing. Particularly, high-spectral-resolution instruments have shown the ability to measure these aerosol properties, e.g., the Infrared Atmospheric Sounding Instrument (IASI). This work reviews six prior laboratory Complex Refractive Index (CRI) datasets, which focus on advancements in laboratory measurement techniques aimed at characterizing dust properties via IASI measurements during a dust storm event over the Gobi Desert in May 2017. We evaluate the sensitivity of IASI to different CRI datasets using the ARAHMIS radiative transfer algorithm and explore their impact on retrieving size distribution parameters by mapping their spatial distribution. The results indicate that the new laboratory CRI datasets decrease the total error by 30 % and that the choice of CRI significantly impacts the accuracy of dust detection and characterization from satellite observations. Notably, datasets that incorporate aerosol generation techniques with higher spectral resolution and samples from the case study region show enhanced compatibility with IASI observations. The outcomes of this research emphasize two key points: the crucial connection between dust's chemical composition and its optical properties, and the need to consider the specific composition of the CRI dataset for improved retrieval of the microphysical parameters. Moreover, this study highlights the critical role of continuous enhancements in CRI measurement approaches, as well as the potential of high-spectral-resolution infrared sounders for aerosol atmospheric investigation and understanding their radiative impacts.