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. We quantitatively describe the
atmospheric transport of CO2 mole fractions during a mid-latitude cold
front passage and explore 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 CO2was located along
the frontal boundary. Observed and simulated 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 transport of CO2 mole fractions along
the frontal boundary. We show that cold front passages lead to large CO2
transport events including a significant contribution from vertical
advection, and that mid-continent frontal boundaries are formed from a
complex mixture of CO2 sources.