Examining Asian dust refractive indices for brightness temperature simulations in the 650–1135 cm−1 spectral range

Abstract

In this paper, we modeled dust impacts on atmospheric radiative transfer in the thermal infrared region of 650–1135 cm−1 by using the radiative transfer for TOVs model (RTTOV). We assessed three sets of Asian dust refractive indices (the Volz refractive index implemented in the RTTOV as default, and the Gobi and Taklamakan refractive indices) for brightness temperature simulations. The US 76 standard profile was employed to represent the atmospheric status. Three scenarios of high (532.6~575.2 hPa), middle (661~703.6 hPa) and low (786.3~825.8 hPa) dust layers and four cases of aerosol optical thickness (AOT) (0.1, 0.5, 1.0, and 1.5 at 1000 cm−1) were considered in the simulations. It was found that the refractive indices have a clear impact on simulating the values and the spectral slope of brightness temperature in the mid-thermal infrared band. Brightness temperature difference (BTD) for different refractive indices (Gobi/Taklamakan–Volz) increases with the height of dust layer and the AOT. The BTD reaches ~4 K for the high dust layer (532.6~575.2 hPa) and the AOT of 1.5. Most BTDs (0.5–4 K) are much larger than the noise-equivalent temperature difference of high-spectral resolution infrared sounders. Even for the AOT of 0.1, BTDs for different refractive indices could be close to or larger than 0.2 K. This study emphasizes the requirement of accurate refractive indices according to dust origins for improving brightness temperature simulations and provides valuable references for potential improvement of dust retrievals.