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\begin{document}

\title{Pyrocumulonimbus Events over British Columbia in 2017: An ensemble model
study of parameter sensitivities and climate impacts of wildfire smoke
in the stratosphere}



\author[1,1]{Hsiang-He Lee}%
\author[1,1]{Katherine A Lundquist}%
\author[2,2]{Qi Tang}%
\affil[1]{Lawrence Livermore National Laboratory}%
\affil[2]{Lawrence Livermore National Laboratory (DOE)}%


\vspace{-1em}



  
  \date{May 16, 2024}


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\begin{abstract}
Pyrocumulonimbus (pyroCb) are fire-triggered or fire-augmented
thunderstorms and can by transporting a large amount of smoke particles
into the lower stratosphere. With satellite remote sensing measurements,
the plumes from pyroCb events over British Columbia in 2017 were
observed in the lower stratosphere for about 8-10 months after the smoke
injections. Several previous studies used global climate models to
investigate the physical parameters for the 2017 pyroCb events, but the
conclusions show strong model dependency. In this study, we use Energy
Exascale Earth System Model (E3SM) atmosphere model version 1 (EAMv1)
and complete an ensemble of runs exploring three injection parameters:
smoke amount, the ratio of black carbon to smoke, and injection height.
Additionally, we consider the heterogeneous reaction of ozone and
primary organic matter. According to the satellite daily observed
aerosol optical depth, we find that the best ensemble member is the
simulation with 0.4 Tg of smoke, 3\% of which is black carbon, a 13.5 km
smoke injection height, and a 10-5 probability factor of the
heterogeneous reaction of ozone and primary organic matter. We use the
Random Forest machine learning technique to quantify the relative
importance of each parameter in accurately simulating the 2017 pyroCb
events and find that the injection height is the most critical feature.
Due to the long lifetime and wide transport of stratospheric aerosols,
the estimated e-folding time of smoke aerosols in the stratosphere is
about 188 days, and the global averaged shortwave surface cooling is
-0.292 W m-2 for about 10 months.%
\end{abstract}%



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