Informed Multi-scale Approach Applied to the British Columbia Fires of
Late Summer 2017
Abstract
Pyrocumulonimbus clouds have a complex origin depending on fire dynamics
and meteorological conditions. When a pyrocumulonimbus (PyroCb) cloud
formation develops and is maintained over a period of time, it can
inject significant aerosol into the troposphere and lower stratosphere,
resulting in longer term (months to years) climate cooling effects. In
this work we investigate the British Columbia and northern Washington
wildfires on August 12-13, 2017 using a multi-scale simulation
framework. We use the output of a physics based wildfire model (FIRETEC)
with parameterized energy, particle, and gas emissions to drive the
upper atmospheric aerosol mass injection within a regional cloud
resolving model (HIGRAD). We demonstrate that vertical motions produced
by latent heat release of the condensation of ice and cloud particles
within the PyroCbs induce another 5 km of lifting of the simulated
aerosol plume. Primary black carbon and organic aerosols alone may not
be enough to explain the observed aerosol burden, thus we show that dust
and ash particles can enhance lofted aerosol mass. Additionally, we show
that semi volatile organic gases emitted by the fires eventually
condense, further increasing the aerosol burden. A simulation with all
aerosol mechanisms active, driven by the observed fuel load and
environmental conditions, reasonably reproduces an aerosol profile
inferred from observational data.