Aircraft vertical profiling of variation of CO2 over a Canadian Boreal Forest Site: a role of advection in the changes in the atmospheric boundary layer CO2 content

During the period of July 8–13, 2002, we collected vertical profiles by aircraft of meteorological variables and atmospheric CO2 over the OBS (old black spruce) site located in Boreal Ecosystem Research and Monitoring Sites in Northern Saskatchewan, Canada.We have used the data from the morning and afternoon flights to calculate the regional daily afternoon CO2 flux for the days July 8–11. These daily fluxes were then compared to those obtained by the boundary layer budget method and by the eddy covariance measurements on the tower at the OBS site.We identified the importance of changes in the CO2 concentration by advection to the flux estimates. In addition, we provide arguments to suggest that subseasonal temporal averaging might not, at least in some cases, eliminate advective bias contribution to the flux estimates. Because the advective influence is large and highly directional, even on seasonal and interannual timescales, it is advisable that flux estimates based on CO2 concentration change at a site contain dynamic description of an air parcel transport history.