The Aerosol Module in the Community Radiative Transfer Model (v2.2 and v2.3): accounting for aerosol transmittance effects on the radiance observation operator

Abstract

Abstract. The Community Radiative Transfer Model (CRTM), a sensor-based radiative transfer model, has been used within the Gridpoint Statistical Interpolation (GSI) system for directly assimilating radiances from infrared and microwave sensors. We conducted numerical experiments to illustrate how including aerosol radiative effects in CRTM calculations changes the GSI analysis. Compared to the default aerosol-blind calculations, the aerosol influences reduced simulated brightness temperature (BT) in thermal window channels, particularly over dust-dominant regions. A case study is presented, which illustrates how failing to correct for aerosol transmittance effects leads to errors in meteorological analyses that assimilate radiances from satellite infrared sensors. In particular, the case study shows that assimilating aerosol-affected BTs significantly affects analyzed temperatures in the lower atmosphere across several regions of the globe. Consequently, a fully cycled aerosol-aware experiment improves 1–5 d forecasts of wind, temperature, and geopotential height in the tropical troposphere and Northern Hemisphere stratosphere. Whilst both GSI and CRTM are well documented with online user guides, tutorials, and code repositories, this article is intended to provide a joined-up documentation for aerosol absorption and scattering calculations in the CRTM and GSI. It also provides guidance for prospective users of the CRTM aerosol option and GSI aerosol-aware radiance assimilation. Scientific aspects of aerosol-affected BT in atmospheric data assimilation are briefly discussed.

Direct assimilation of AVHRR satellite radiance measurements in a reanalysis system

“…The process of assimilation of AVHRR radiance in a reanalysis system is described briefly in the next section. Tang et al, 2017;Stegmann et al, 2018;Stegmann et al, 2022;Lu et al, 2022;Nalli et al, 2022;Moradi et al, 2022;Karpowicz et al, 2022). The CRTM takes skin SST as an input, as well as the atmospheric profile and aerosol properties of the column.…”

“…All satellite observations are directly assimilated by Gridpoint Statistical Interpolation software (GSI; Kleist et al ., 2009) using Community Radiative Transfer Model (CRTM; Tang et al ., 2017; Stegmann et al ., 2018; Stegmann et al ., 2022; Lu et al ., 2022; Nalli et al ., 2022; Moradi et al ., 2022; Karpowicz et al ., 2022). The CRTM takes skin SST as an input, as well as the atmospheric profile and aerosol properties of the column.…”