The Genesis and Impact of Pyrocumulonimbus: Insights from DOE’s Novel Multiscale Simulation Framework

Extreme wildfire-generated pyrocumulonimbus (pyroCb) firestorms play a critical role in injecting smoke aerosols into the upper troposphere and lower stratosphere, significantly influencing their trajectory and lifetime. This phenomenon introduces uncertainties in evaluating the impacts of wildfires on climate and air quality. Despite their significance, accurately representing pyroCb firestorms in global Earth system models (ESMs) remains challenging due to coarse grid spacing, missing essential physical processes, and uncertainties in fire heat and aerosol emission estimates.

In this study, we introduce a novel global multiscale wildfire simulation framework that leverages the capabilities of the US Department of Energy (DOE) Energy Exascale Earth System Model (E3SM). This framework incorporates a non-hydrostatic dynamic core, a regionally refined mesh (3 km resolution in California and 100 km elsewhere), and interactive chemistry/aerosol components, supported by a high-resolution (hourly, 500 m) wildfire observational dataset derived from satellite data. We assessed this framework by simulating the Creek Fire event in California in 2020. The simulation aligned well with observations, including satellite brightness temperature data and NEXRAD measurements.

Our analyses reveal that fire-induced vertical moisture transport, the high-resolution wildfire emission dataset, and middle atmosphere moisture are essential for accurately capturing pyroCb events. Furthermore, the evaluation of simulated ozone and PM2.5 concentrations against local observations, along with an analysis of the transport and climate impacts of fire-induced black and organic carbon aerosols, underscores the framework's effectiveness in enhancing our understanding of the genesis and across-scale impacts of pyrocumulonimbus events.

This work is performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.