A regional high-resolution carbon flux inversion of North America for 2004

A E Schuh,I T Baker,N Parazoo,M Uliasz,D E J Worthy,K D Corbin,A S Denning,A E Andrews

doi:10.5194/bg-7-1625-2010

Abstract

Abstract. Resolving the discrepancies between NEE estimates based upon (1) ground studies and (2) atmospheric inversion results, demands increasingly sophisticated techniques. In this paper we present a high-resolution inversion based upon a regional meteorology model (RAMS) and an underlying biosphere (SiB3) model, both running on an identical 40 km grid over most of North America. Current operational systems like CarbonTracker as well as many previous global inversions including the Transcom suite of inversions have utilized inversion regions formed by collapsing biome-similar grid cells into larger aggregated regions. An extreme example of this might be where corrections to NEE imposed on forested regions on the east coast of the United States might be the same as that imposed on forests on the west coast of the United States while, in reality, there likely exist subtle differences in the two areas, both natural and anthropogenic. Our current inversion framework utilizes a combination of previously employed inversion techniques while allowing carbon flux corrections to be biome independent. Temporally and spatially high-resolution results utilizing biome-independent corrections provide insight into carbon dynamics in North America. In particular, we analyze hourly CO2 mixing ratio data from a sparse network of eight towers in North America for 2004. A prior estimate of carbon fluxes due to Gross Primary Productivity (GPP) and Ecosystem Respiration (ER) is constructed from the SiB3 biosphere model on a 40 km grid. A combination of transport from the RAMS and the Parameterized Chemical Transport Model (PCTM) models is used to forge a connection between upwind biosphere fluxes and downwind observed CO2 mixing ratio data. A Kalman filter procedure is used to estimate weekly corrections to biosphere fluxes based upon observed CO2. RMSE-weighted annual NEE estimates, over an ensemble of potential inversion parameter sets, show a mean estimate 0.57 Pg/yr sink in North America. We perform the inversion with two independently derived boundary inflow conditions and calculate jackknife-based statistics to test the robustness of the model results. We then compare final results to estimates obtained from the CarbonTracker inversion system and at the Southern Great Plains flux site. Results are promising, showing the ability to correct carbon fluxes from the biosphere models over annual and seasonal time scales, as well as over the different GPP and ER components. Additionally, the correlation of an estimated sink of carbon in the South Central United States with regional anomalously high precipitation in an area of managed agricultural and forest lands provides interesting hypotheses for future work.

Highlights

Carbon dioxide inversion studies have generally been focused on improved estimation of terrestrial carbon fluxes such as Ecosystem Respiration (ER), Gross Primary Production (GPP), and Net Ecosystem Exchange (NEE) as a means to better understand the carbon cycle of the earth
We choose to present one particular case with a fixed set of inversion inputs as an initial case study and use it to compare the effect of varying the boundary inflow and the source of the domain fossil fuel fluxes
Gross Primary Productivity (GPP), ER, and NEE flux corrections implied by this inversion provide posterior annual NEE estimates similar to those provided by a number of independently derived models including Carnegie Ames Stanford Approach (CASA) and the Moderate Resolution Imaging Spectroradiometer (MODIS) 17 GPP product

Summary

Introduction

Carbon dioxide inversion studies have generally been focused on improved estimation of terrestrial carbon fluxes such as Ecosystem Respiration (ER), Gross Primary Production (GPP), and Net Ecosystem Exchange (NEE) as a means to better understand the carbon cycle of the earth. Schuh et al.: A regional high-resolution carbon flux inversion over the past decade. Inversion studies were focused primarily with finding an explanation for the missing sink of carbon that can be identified from calculating a budget from annual fossil fuel emissions to the atmosphere, the effect of land use changes, and the oceanic carbon sink and comparing it to annual records of increasing atmospheric carbon dioxide concentrations. The data available for regional inversion studies is increasing rapidly year after year, primarily within the developed industrial nations of the Northern Hemisphere. This provides researchers with some of the first opportunities to perform inversion studies in a very high-resolution setting

Methods

Results

Conclusion