Carbon dioxide distribution, origins, and transport along a frontal
boundary during summer in mid-latitudes
Abstract
Synoptic weather systems are a major driver of spatial gradients in
atmospheric CO2 mole fractions. During frontal passages air masses from
different regions meet at the frontal boundary creating significant
gradients in CO2 mole fractions. This study quantitatively describes the
atmospheric transport of CO2 mole fractions during a mid-latitude cold
front passage and explores the impact of various sources of CO2. We
focus here on a cold front passage over Lincoln, Nebraska on August 4th,
2016 observed by aircraft during the Atmospheric Carbon and Transport
(ACT)-America campaign. A band of air with elevated CO2 was located
along the frontal boundary. Differences in CO2 across the front were as
high as 25 ppm. Numerical simulations using WRF-Chem at cloud resolving
resolutions (3km) coupled with CO2 surface fluxes and boundary
conditions from CarbonTracker (CT-NRTv2017x) were performed to explore
atmospheric transport at the front. Model results demonstrate that the
frontal CO2 difference in the upper troposphere can be explained largely
by inflow from outside of North America. This difference is modified in
the atmospheric boundary layer and lower troposphere by continental
surface fluxes, dominated in this case by biogenic and fossil fuel
fluxes. Horizontal and vertical advection are found to be responsible
for the distribution of CO2 mole fractions along the frontal boundary.
This study highlights the use of high-resolution simulations in
capturing CO2 transport along a frontal boundary.