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 IR sensors. In particular, the case study shows that assimilating aerosol-affected BTs affects analyzed temperatures in the lower atmosphere significantly in several different regions of the globe. Consequently, a fully-cycled aerosol-aware experiment improves 1–5 day 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.
Highlights
An accurate and computationally efficient radiative transfer model is essential in radiance assimilation for supporting weather prediction, physical retrievals for satellite environmental data records, and inter-comparison among remote sensing sensors.The Community Radiative Transfer Model (CRTM) is a sensor-based radiative transfer model (Weng, 2007; Han et al, 2007).(GSI, Wu et al, 2002; Kleist et al, 2009) system for directly assimilating radiances from infrared (IR) and microwave (MW)sensors
To illustrate how an aerosol transmittance correction is required within satellite radiances assimilated into meteorological data assimilation systems, we present a detailed analysis of a single-cycle Gridpoint Statistical Interpolation (GSI) experiment using GOCART fields from MERRA-2 on 12Z June 22, 2020
This time is chosen because it captures a strong Saharan dust loading event that covers the trans-Atlantic region
Summary
An accurate and computationally efficient radiative transfer model is essential in radiance assimilation for supporting weather prediction, physical retrievals for satellite environmental data records, and inter-comparison among remote sensing sensors. The Community Radiative Transfer Model (CRTM) is a sensor-based radiative transfer model (Weng, 2007; Han et al, 2007). (GSI, Wu et al, 2002; Kleist et al, 2009) system for directly assimilating radiances from infrared (IR) and microwave (MW). Clear-sky radiance calculations are carried out within the CRTM given the atmospheric scattering and absorption profile, surface emissivity and reflectivity, and source functions. CRTM is not designed to describe longwave and shortwave broadband radiative transfer for general circulation model applications. It is developed to support satellite radiance data assimilation and satellite retrieval development
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