Temporal and Spatial Variability in Regional-Scale CO2 Mixing Ratios as Measured During the Mid-Continental Intensive Study
Abstract
The study of regional-scale CO2 concentrations and fluxes is between the detailed understanding of ecological processes that can be gathered via intensive local field study, and the overarching but mechanistically poor understanding of the global carbon cycle that is gained by analyzing the atmospheric CO2 budget. Regional studies are important both to merge these processes and global understanding the carbon cycle, and to monitor regional CO2 emissions control programs. This work is part of the NACP's Midcontinental Intensive (MCI) study. Specifically it adds a regional network of five communications-tower based atmospheric CO2 observations ("Ring 2") from April 2007 through October 2008 to the long-term atmospheric CO2 observing network (tall towers, aircraft profiles, and well- calibrated CO2 measurements on Ameriflux towers) in the mid-continent intensive region. The Ring 2 measurements are based on relatively new technology for CO2 measurement, cavity ring-down spectroscopy (Picarro, Inc.), and the locations are regional in scale (roughly a 500-km diameter ring). We present results concerning data quality of the new instruments, including water vapor correction and uncertainties, as well as small-scale temporal and spatial variations that can be seen with this unique network. For example, the daily daytime average throughout the 2007 and 2008 growing seasons indicated a 50-ppm seasonal drawdown, with significant synoptic variability. The drawdown in this largely agricultural region (heavily influenced by corn) is significantly larger than the 20-30 ppm typically seen in forested regions. Also during the 2007 and 2008 growing seasons, the CO2 mixing ratio at the sites nearly always differ by more than 5 ppm, while at times the inter-site difference is as large as 30-50 ppm. While variability in the regional spatial gradients is expected because of synoptic changes and differing source regions, the magnitude observed is surprisingly large given the sites' relative proximity. This has important implications for the design of regional and perhaps continental observing systems. We also review our past work on the impact of vertical gradients within the atmospheric boundary layer 4on observational system design, and re-examine past conclusions in light of this new hybrid (flux tower, mid-altitude communications tower, tall tower) data set.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.A31I..04M
- Keywords:
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- 0426 Biosphere/atmosphere interactions (0315);
- 4227 Diurnal;
- seasonal;
- and annual cycles (0438);
- 4806 Carbon cycling (0428)