During August of 2000, COBRA conducted in-situ airborne measurements of CO2, CO, H2O, and meteorological parameters in the lower- and mid-troposphere over the U.S., exploring methods for quantifying terrestrial sources and sinks of CO2 at regional and continental scales. In addition, flask measurements of O2/N2 (Scripps) and CH4, N2O, SF6, d13C (NOAA CMDL) were conducted.
The COBRA airborne platform is the University of North Dakota Cessna Citation II, a straight-wing twin-engine fanjet suited for intensive vertical profiling of the entire atmosphere including the PBL (planetary boundary layer). The flight duration of 3.5~4 hours allows coverage of continental scales. In addition to the science payload, the plane carries two pilots and two science crew.
In COBRA-2000, flights originated at Grand Forks, ND, the home base for the UND Citation II. A Lagrangian experiment was performed first, in Southern Manitoba and North Dakota. After a transit to Centennial Airport near Denver, a day was spent surveying through Wyoming and Idaho. Then a transit (Southern tier survey) was executed from Denver to Boston (Hanscom Field), with numerous dips and stops. Next two days of regional flying were conducted over Maine. Finally a survey was made across the Northern Tier states back to Grand Forks, ending with regional Lagrangian flights over the tall tower at WLEF.
Lagrangian Regional-scale Experiment
Airmass-following (Lagrangian) experiments possess the potential for minimizing the advection term in the budget. We tested this Lagrangian approach in COBRA-2000 by conducting several flights sampling an air mass for 12 - 24 hours. We developed and used STILT model to simulate the motions of tracer particles backwards in time and used it to follow an airmass through a 24hour period.
Large-scale Surveys
Two large-scale, trans-continental surveys were conducted in COBRA-2000. The sampling strategy generated cross-sections showing distinct fingerprints of influences at the continental scale. Moreover, results show how signatures of underlying sources and sinks are clearly observable in the atmosphere using aircraft sampling.