Implementation of Dynamic Fire Injection Height in GFDL’s Atmospheric
Model (AM4.0): Impacts on Aerosol Profiles and Radiation
Abstract
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 meters).
Aerosol Optical Depth (AOD) is systematically underestimated due to
biases in the emission dataset, 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 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.