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CO2 Time Series (CT2009)
Site         Year
ALT_06C0: Quasi-continuous, surface measurements from Alert, Nunavut, Canada located at 82.4508N, 62.5072W and 185.00 masl. Measurements are made by Environment Canada (EC). Assimilation statistics for this and other sites are included in the Documentation.

Time series of CO2 mole fractions, both simulated and observed, at this CarbonTracker observation site. In the top panel, measured mole fractions (open black circles) are plotted along with CarbonTracker simulated values (light blue open circles). At some sites, there are observations that CarbonTracker can not simulate successfully; these are shown as filled red circles. The observations corresponding to these rejected simulated values are shown with open red circles. The bottom panel shows a time series of residuals--the difference between the simulated and measured mole fractions--shown with dark green open circles. These residuals should be uncorrelated in time, unbiased (i.e., have a mean of zero), and distributed normally. Also shown in the lower panel is the imposed model-data mismatch (orange lines), which in part defines the rejection criterion (see documentation). Any model first guess value which is more than three times the MDM away from zero, after accounting for potential adjustments to the simulated value due to optimizing fluxes, is rejected by the optimization system. Rejected values, if there are any, are shown with filled red circles.

Seasonal histograms of the residuals at this site. See caption for top figure for the definition of residuals. The left panel collects all residuals for each northern hemisphere summer (June through September); the right panel is the northern hemisphere winter (November through April). Residuals before 1 Jan 2001 are excluded from this analysis to avoid an effect of CarbonTracker burn-in from a poorly-known initial CO2 distribution. The tan color shows the histogram of the residuals themselves; the blue lines and statistics shown in blue text are a summary of the residuals interpreted as a normal distribution. The assumed model-data mismatch is shown in green (lines and text). The vertical scales are relative, determined by the number of observations and how tightly they are grouped, with the area under the histogram forced to unity.