COBRA was designed to test concepts for determining the regional- and continental-scale fluxes for CO2, CO, and other gases using aircraft in situ measurements, and to be a pathfinder for future remote-sensing techniques for CO2 determination. All concepts involve repeated vertical soundings of the atmosphere, either over diurnal cycles in one place or over a large land area. Descents to small airports are employed to reach the lowest altitudes (“missed approaches”). When available, towers with continuous data in the domain of the experiment, provide concentrations (to get the lower part of the profiles) and fluxes (determine the bias associated with restrictions on suitable flight conditions).
COBRA takes a three pronged approach to quantify fluxes of CO2 :
- Eulerian column budgets : Vertical profiles at different times of the day over selected locations yield first-order estimates of carbon fluxes and define the diurnal variations for each region. This simple approach assumes that the net contribution from horizontal advection is small on average for many days of data.
- Lagrangian regional experiments: Regions upstream of a receptor location were sampled, following the motion of the air, to eliminate the influence from horizontal advection. Airmass locations were predicted with an operational flight planning tool, a stochastic particle transport model driven with forecasted meteorology from the Eta and AVN models. Diurnal airborne measurements of CO2, CO and H2O within and above the PBL (planetary boundary layer) in an airmass-following framework yield regional fluxes and their variations across different disturbance regimes.
- Large-scale surveys: Sampling of large-scale CO2 distribution along the synoptic flow pattern, combined with knowledge of diurnal variations from the Eulerian experiments, give continental (3000km) and/or basin (1000km) scale fluxes
In our future project in the Amazon, Hemispheric-scale cross-sections will be conducted: observations during transit flights between North Dakota and Brazil will enable construction of CO2 cross sections that span from the mid- to tropical latitudes.