Refining the Global Picture: the Impact of Increased Resolution on CO₂
Atmospheric Inversions using OCO-2 XCO₂ retrievals
Abstract
The threat posed by the increasing concentration of carbon dioxide
(CO₂) in the atmosphere motivates a detailed and precise estimation of
CO₂ emissions and absorptions over the globe. This study refines the
spatial resolution of the CAMS/LSCE inversion system, achieving a global
resolution of 0.7° latitude and 1.4° longitude, or three times as many
grid boxes as the current operational setup. In a two-year inversion
assimilating the midday clear-sky retrievals of the column-average
dry-air mole fraction of carbon dioxide (XCO₂) from NASA’s second
Orbiting Carbon Observatory (OCO-2), the elevated resolution
demonstrates an improvement in the representation of atmospheric CO₂,
particularly at the synoptic time scale, as validated against
independent surface measurements. Vertical profiles of the CO₂
concentration differ slightly above 22 km between resolutions compared
to AirCore profiles, and highlight differences in the vertical
distribution of CO₂ between resolutions. However, this disparity is not
evident for XCO₂, as evaluated against independent reference
ground-based observations. Global and regional estimates of natural
fluxes for 2015-2016 are similar between the two resolutions, but with
North America exhibiting a higher natural sink at high-resolution for
2016. Overall, both inversions seem to yield reasonable estimates of
global and regional natural carbon fluxes. The increase in calculation
time is less than the increase in the number of operations and in the
volume of input data, revealing greater efficiency of the code executed
on a Graphics Processing Unit. This allows us to make this higher
resolution the new standard for the CAMS/LSCE system.