Two large-scale, trans-continental surveys were conducted in COBRA-2000, a southern tier transect from Idaho to Maine and a northern tier run from Maine to North Dakota (see flight tracks). The Citation cruised in the free troposphere, sounding the atmosphere vertically at ~200 km intervals using "missed approaches" to airports on the way.

This sampling strategy generated cross-sections showing distinct fingerprints of influences at the continental scale. During the northern survey we sampled air from southern Canada, where climatic conditions were favorable for vegetation to take up CO₂ in August. Clear signatures of CO₂ uptake were seen for ~1000 km, prominently the persistent deficit (4 - 10 ppm) of CO₂ in the lowest 2-3 km of the atmosphere. A notable exception (-87° to -83° W) shows the influence of the Great Lakes, neither strong sources nor sinks for CO₂ in August. This exception provides evidence that the CO₂ deficit seen in the PBL and residual layer develops at time scales slightly longer than the 1-2 days transit time for air over the Great Lakes. The southern survey sampled air arriving from the west, southwest and south. These regions were affected by strong seasonal drought. Conditions were also cloudy in much of the region just upwind of the flights. Unfavorable growing conditions, combined with emissions of CO₂ from fossil fuel combustion, translated into enhancements of CO₂ across the whole southern cross-section.

These results unambiguously suggest that signatures of underlying sources and sinks are clearly observable in the atmosphere using aircraft sampling. With the recently developed STILT (Stochastic Time-Inverted Lagrangian Transport) model these signatures can be quantitatively linked to the upwind sources and sinks.

More information can be found in our Exhibit Hall.