Abstract
Abstract. Observations of gradients in the total CO2 column, 〈CO2〉, are expected to provide improved constraints on surface fluxes of CO2. Here we use a general circulation model with a variety of prescribed carbon fluxes to investigate how variations in 〈CO2〉 arise. On diurnal scales, variations are small and are forced by both local fluxes and advection. On seasonal scales, gradients are set by the north-south flux distribution. On synoptic scales, variations arise due to large-scale eddy-driven disturbances of the meridional gradient. In this case, because variations in 〈CO2〉 are tied to synoptic activity, significant correlations exist between 〈CO2〉 and dynamical tracers. We illustrate how such correlations can be used to describe the north-south gradients of 〈CO2〉 and the underlying fluxes on continental scales. These simulations suggest a novel analysis framework for using column observations in carbon cycle science.
Highlights
Diagnosing the patterns and trends in the flux of carbon dioxide, CO2, between the land or ocean and the atmosphere is a longstanding interest of the carbon cycle community
Atmospheric transport models are used to simulate global CO2 fields, given estimates of regional CO2 fluxes owing to fossil fuel emissions, ocean-atmosphere exchange, and biosphere-atmosphere exchange; the estimated fluxes are adjusted to best match the observations
Given that the stratosphere only represents ∼15–20% of the midlatitude atmospheric column mass, this represents sufficient agreement for our purposes. We show both global CO2 fields and CO2 sampled from the model at locations that are part of the Total Carbon Column Observing Network (TCCON)
Summary
Diagnosing the patterns and trends in the flux of carbon dioxide, CO2, between the land or ocean and the atmosphere is a longstanding interest of the carbon cycle community. Such information is needed, for example, to evaluate models of future climate and for evaluating the effectiveness of proposed climate change mitigation strategies. Inverse modeling represents one approach for estimating regional and global carbon fluxes from gradients in the observed concentration (or mixing ratio) of CO2, [CO2] (Gurney et al, 2002, 2004). Observations of column CO2 from remote sensing platforms such as GOSAT and OCO-2 (Yokota et al, 2009; Crisp et al, 2004) and from ground-based observatories are anticipated to provide better constraints on the exchange of CO2 between the atmosphere and the surface (Olsen and Randerson, 2004; Chevallier et al, 2007)
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