07 Nov 2022
07 Nov 2022
Status: this preprint is currently under review for the journal ACP.

Uncertainty in Parameterized Convection Remains a Key Obstacle for Estimating Surface Fluxes of Carbon Dioxide

Andrew E. Schuh1 and Andrew R. Jacobson2,3 Andrew E. Schuh and Andrew R. Jacobson
  • 1Cooperative Institute for Research in the Atmosphere (CIRA), Colorado State University, Fort Collins, CO USA
  • 2CIRES, University of Colorado, Boulder, CO USA
  • 3NOAA Global Monitoring Laboratory, Boulder, CO USA

Abstract. The analysis of observed atmospheric trace gas mole fractions to infer surface sources and sinks of chemical species relies heavily on simulated atmospheric transport. The chemical transport models (CTMs) used in flux inversion models are commonly configured to reproduce the atmospheric transport of a general circulation model (GCM) as closely as possible. CTMs generally have the dual advantages of computational efficiency and improved tracer conservation compared to their parent GCMs, but they usually simplify the representations of important processes. This is especially the case for high-frequency vertical motions associated with diffusion and convection. Using common-flux experiments, we quantify the importance of parameterized vertical processes for explaining systematic differences in tracer transport between two commonly-used CTMs. We find that differences in convection are strongly correlated with the differences in modeled column CO2. The parameterization of diffusion is more important near the surface due to its role in representing PBL mixing. Accordingly, near-surface in situ measurements are more strongly impacted by this process than are total-column retrievals. Both diffusive and convective vertical mixing tend to ventilate the lower atmosphere, so near-surface measurements may only constrain the net vertical mixing and not the balance between these two processes. Remote sensing-based retrievals of total column CO2, with their increased sensitivity to convection, may provide important new constraints on parameterized vertical motions.

Andrew E. Schuh and Andrew R. Jacobson

Status: open (until 19 Dec 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-616', Anonymous Referee #1, 20 Nov 2022 reply

Andrew E. Schuh and Andrew R. Jacobson

Andrew E. Schuh and Andrew R. Jacobson


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Short summary
A comparison of atmospheric carbon dioxide concentrations resulting from two different atmospheric transport models showed large differences in predicted concentrations with significant space-time correlations. The vertical mixing of long-lived trace gases by convection was determined to be the main driver of these differences. The resulting uncertainty was deemed significant to the application of using atmospheric gradients of CO2 to estimate surface fluxes of CO2.