Implementation of Dynamic Fire Injection Height in GFDL's Atmospheric Model (AM4.0): Impacts on Aerosol Profiles and Radiation

Wildfires inject aerosols into the atmosphere at varying altitudes, modifying long-range transport, which impacts Earth's climate system and air quality. Most global climate models use prescribed fixed-height injections, not accounting for the dynamic variability of wildfires. In this study, we enhance the injection method of biomass burning aerosols implemented in the Geophysical Fluid Dynamic Laboratory's Atmospheric Model version 4.0, shifting to a more mechanistic approach. We test several injection height schemes to assess their impact on the Earth's radiation budget by performing 18-year global simulations. Comparison of modeled injection height from the mechanistic scheme with observations indicates error within instrumental uncertainty (less than 500 m). Aerosol Optical Depth is systematically underestimated due to biases in the emission data set, but the mechanistic scheme significantly reduces this bias by up to 0.5 optical depth units during extreme wildfire seasons over boreal forests. In term of the vertical profile of the aerosol extinction coefficient, a comparison with satellite observations indicates significant improvement below 4 km altitude. Dynamic injection of biomass burning emissions changed the net clear-sky radiative flux at top of the atmosphere regionally (±1.5 Wm⁻²) and reduced it by −0.38 Wm⁻² at the surface globally, relative to a baseline with no fire emissions. The temperature gradient anomaly associated with the dynamic injection of absorbing aerosols affects the atmospheric stability and circulation patterns. This study highlights the need to implement dynamic injection of fire emissions to simulate more accurately the atmospheric distribution of aerosols and their interactions with Earth's climate system.