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\begin{document}

\title{Seasonal strength of terrestrial net ecosystem CO2 exchange from North
America is underestimated in global inverse modeling}



\author[1]{Yuyan Cui}%
\author[1]{Li Zhang}%
\author[2]{Andrew R Jacobson}%
\author[3]{Matthew S Johnson}%
\author[3]{Sajeev Philip}%
\author[4]{David Baker}%
\author[5]{Frederic Chevallier}%
\author[4]{Andrew E Schuh}%
\author[6]{Junjie Liu}%
\author[7]{Sean Crowell}%
\author[7]{Helene Peiro}%
\author[8]{Feng Deng}%
\author[9]{Sourish Basu}%
\author[1]{Kenneth J Davis}%
\affil[1]{The Pennsylvania State University}%
\affil[2]{NOAA/GML/CIRES}%
\affil[3]{NASA Ames Research Center}%
\affil[4]{Colorado State University}%
\affil[5]{Laboratoire des Sciences du Climat et de l'Environnement (LSCE)}%
\affil[6]{Jet Propulsion Laboratory}%
\affil[7]{University of Oklahoma}%
\affil[8]{University of Toronto}%
\affil[9]{NASA GSFC GMAO / University of Maryland}%


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  \date{June 10, 2024}


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\begin{abstract}
We evaluate terrestrial net ecosystem-atmosphere exchange (NEE) of CO2
from nine global inversion systems that inferred fluxes from four CO2
observational sources. We use 98 flights in the central and eastern U.S.
from the ACT-America aircraft mission to conduct this sub-continental,
seasonal-scale evaluation. We use Lagrangian particle dispersion
modeling (FLEXPARTv10.4-ERA-Interim) to compare observed and simulated
regional biogenic CO2 mole fractions. We find a positive bias (modeled
CO2 \textgreater{} observed) in the summer and negative bias (modeled
CO2 \textless{} observed) in dormant seasons across most flux products,
suggesting that the seasonal strength of CO2 NEE is underestimated in
these inverse models. Fluxes inferred from OCO-2 v9 satellite land
nadir/glint observations yield an error level that is similar to fluxes
inferred from in-situ data. Large bias errors are observed in the
croplands and eastern forests. Future experiments are needed to
determine if these seasonal biases are associated with biases in net
annual flux estimates.%
\end{abstract}%



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