Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 17, 5561-5581, 2017
http://www.atmos-chem-phys.net/17/5561/2017/
doi:10.5194/acp-17-5561-2017
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
03 May 2017
How can mountaintop CO2 observations be used to constrain regional carbon fluxes?
John C. Lin1, Derek V. Mallia1, Dien Wu1, and Britton B. Stephens2 1Department of Atmospheric Sciences, University of Utah, Salt Lake City, Utah 84112, USA
2Earth Observing Laboratory, National Center for Atmospheric Research, Boulder, Colorado 80301, USA
Abstract. Despite the need for researchers to understand terrestrial biospheric carbon fluxes to account for carbon cycle feedbacks and predict future CO2 concentrations, knowledge of these fluxes at the regional scale remains poor. This is particularly true in mountainous areas, where complex meteorology and lack of observations lead to large uncertainties in carbon fluxes. Yet mountainous regions are often where significant forest cover and biomass are found – i.e., areas that have the potential to serve as carbon sinks. As CO2 observations are carried out in mountainous areas, it is imperative that they are properly interpreted to yield information about carbon fluxes. In this paper, we present CO2 observations at three sites in the mountains of the western US, along with atmospheric simulations that attempt to extract information about biospheric carbon fluxes from the CO2 observations, with emphasis on the observed and simulated diurnal cycles of CO2. We show that atmospheric models can systematically simulate the wrong diurnal cycle and significantly misinterpret the CO2 observations, due to erroneous atmospheric flows as a result of terrain that is misrepresented in the model. This problem depends on the selected vertical level in the model and is exacerbated as the spatial resolution is degraded, and our results indicate that a fine grid spacing of ∼ 4 km or less may be needed to simulate a realistic diurnal cycle of CO2 for sites on top of the steep mountains examined here in the American Rockies. In the absence of higher resolution models, we recommend coarse-scale models to focus on assimilating afternoon CO2 observations on mountaintop sites over the continent to avoid misrepresentations of nocturnal transport and influence.

Citation: Lin, J. C., Mallia, D. V., Wu, D., and Stephens, B. B.: How can mountaintop CO2 observations be used to constrain regional carbon fluxes?, Atmos. Chem. Phys., 17, 5561-5581, doi:10.5194/acp-17-5561-2017, 2017.
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Short summary
Mountainous areas can potentially serve as regions where the key greenhouse gas, carbon dioxide (CO2), can be absorbed from the atmosphere by vegetation, through photosynthesis. Variations in atmospheric CO2 can be used to understand the amount of biospheric fluxes in general. However, CO2 measured in mountains can be difficult to interpret due to the impact from complex atmospheric flows. We show how mountaintop CO2 data can be interpreted by carrying out a series of atmospheric simulations.
Mountainous areas can potentially serve as regions where the key greenhouse gas, carbon dioxide...
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