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Title: Advective transport of CO2 in permeable media induced by atmospheric pressure fluctuations: 2. Observational evidence under snowpacks
Author: Massman, W. J.; Frank, J. M.
Source: Journal of Geophysical Research. 111: G03005.
Description: Meadow and forest CO2 amounts sampled beneath an approximately meter deep (steady state) snowpack at a subalpine site in southern Rocky Mountains of Wyoming are observed to vary by nearly 200 ppm over periods ranging from 4 to 15 days. This work employs the model of periodic, pressure-induced, advective transport in permeable media developed in part 1 of this study to investigate these CO2 fluctuations. With the aid of this physically based model, inferences are made about the nature of the physical properties of both the forcing mechanism and the snowpack that contribute to these periodic variations in undersnow CO2. Results are consistent with the hypothesis that the undersnow CO2 is being driven by advective flows induced by pressure fields created when the wind interacts with the local aerodynamic roughness elements (nearby mountain peaks, forest edges, snowdrifts). Nonharmonic spectral and cospectral techniques indicate that the wind modulates the low-frequency temporal dynamics of the undersnow CO2, whereas comparisons of the modeled and observed time lag between the surface forcing and the response of the undersnow CO2 suggest that site topography determines the horizontal structure of the wind (surface pressure) forcing. It is also suggested here that the snowpack is at most a weakly dispersive medium. Finally, because the model includes a CO2 source term in the soil underlying the snowpack, other findings suggest that both the wintertime CO2 fluxes emanating from the snowpack and the soil respiration rates may vary significantly between a meadow soil and a forest soil at this site.
Keywords: undersnow CO2 fluctuations, snowpack, subalpine ecosystem, diffusion, dispersivity, windpumping, wintertime soil respiration
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Massman, W. J.; Frank, J. M. 2006. Advective transport of CO2 in permeable media induced by atmospheric pressure fluctuations: 2. Observational evidence under snowpacks. Journal of Geophysical Research. 111: G03005.
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