Quantifying the Direct Radiative Effect of Absorbing Aerosols for Numerical Weather Prediction: A Case Study

We conceptualize aerosol radiative transfer processes arising from the hypothetical coupling of a global aerosol transport model and global numerical weather prediction model by applying the U.S. Naval Research Laboratory Navy Aerosol Analysis and Prediction System (NAAPS) and the Navy Global Environmental Model (NAVGEM) meteorological and surface reflectance fields. A unique experimental design during the 2013 NASA Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC⁴RS) field mission, allowed for collocated airborne sampling by the Langley’s High Spectral Resolution Lidar (HSRL), the Airborne Multi-angle Spectro Polarimetric Imager (AirMSPI), up/down SW and broadband IR radiometers, as well as NASA A-Train support from the Moderate Resolution Imaging Spectroradiometer (MODIS), to compare model radiative forcing properties with situ observations. We were able to achieve radiative column closure with the observations, making this case study an ideal one for evaluating model performance.

Our results demonstrate the sensitivity that different aerosol distributions exhibit on radiative fluxes and heating rates, specifically those associated with solar-absorbing smoke and urban aerosols. Due to the nature of the dominant aerosols in this study, we observed a reduction of the net SW radiation with the HSRL profile of -33.00 W m^-2, and between -22.75 W m^-2 and -4.00 W m^-2 with different variants of the NAAPS model. Instantaneous heating rates for the NAAPS model runs peaked around 7 K day^-1 in the lower part of the troposphere, while the HSRL profiles resulted in values of up to 18 K day^-1 in the middle of the troposphere --highlighting the importance of obtaining of accurate and realistic aerosol vertical distributions. Limitations are identified with respect to aerosol attribution, vertical distribution and choice of optical and surface polarimetry properties, which are discussed within the context of their influence on NWP and is particularly relevant as the community propels forward towards inline aerosol modelling within global forecast systems.