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\begin{document}

\title{Improving the parameterization of dust emission threshold in the
Community Earth System Model (CESM)}



\author[1]{Danny Min Leung}%
\author[1]{Jasper Kok}%
\author[2]{Longlei Li}%
\author[2]{Natalie Mahowald}%
\author[3]{Laurent MENUT}%
\author[4]{Catherine Prigent}%
\author[5]{Martina Klose}%
\author[6]{Carlos Pérez García-Pando}%
\author[7]{David Lawrence}%
\affil[1]{University of California, Los Angeles}%
\affil[2]{Cornell University}%
\affil[3]{Laboratoire de Météorologie Dynamique}%
\affil[4]{Observatoire de Paris-Meudon}%
\affil[5]{Barcelona Supercomputing Center}%
\affil[6]{ICREA, Catalan Institution for Research and Advanced Studies}%
\affil[7]{National Center for Atmospheric Research}%


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  \date{May 23, 2024}


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\begin{abstract}
A key challenge in accurate simulations of desert dust emission is the
parameterization of the threshold wind speed above which dust emission
occurs. However, the existing parameterizations yield a unrealistically
low dust emission threshold in some climate models such as the Community
Earth System Model (CESM), leading to higher simulated dust source
activation frequencies than observed and requiring global tuning
constants to scale down dust emissions. Here we develop a more realistic
parameterization for the dust emission threshold in CESM. In particular,
we account for the dissipation of surface wind momentum by surface
roughness elements such as vegetation, rocks, and pebbles, which reduce
the wind momentum exerted on the bare soil surface. We achieve this by
implementing a dynamic wind drag partition model by considering the
roughness of the time-varying vegetation as quantified by the leaf area
index (LAI), as well as the time-invariant rocks and pebbles using
satellite-derived aeolian roughness length. Furthermore, we account for
the effect of soil size on dust emission threshold by replacing the
currently used globally constant soil median diameter with a spatially
varying soil texture map. Results show that with the new
parameterization dust emissions decrease by 20--80\% over source regions
such as Africa, Middle East, and Asia, thereby reducing the need for the
global tuning constant. Simulated dust emissions match better in both
spatiotemporal variability and emission frequency when compared against
satellite observed dust activation frequency data. Our results suggest
that including more physical dust emission parameterizations into
climate models can lessen bias and improve simulation results, possibly
eliminate the use of empirical source functions, and reduce the need for
tuning constants. This development could improve assessments of dust
impacts on the Earth system.%
\end{abstract}%



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