Grid-type flight patterns at an altitude of 30 m were executed in the summer of 1991 by the Canadian Twin Otter flux research aircraft over a 15 km x 16.1 km agricultural area, as part of the California ozone deposition experiment (CODE). This permitted the mapping, by eddy covariance techniques, of surface-atmosphere exchange for sensible heat, moisture, CO2 and ozone, in the form of GIS-interpolated flux maps and in the discrete form of those coherent structures of the turbulent transfer process that dominate these exchange processes. The magnitude of surface-related mesoscale contributions to the flux was also quantified. Flux observations were compared against radiometrically observed surface temperatures and vegetation indices (NDVI and VI), observed from aircraft and satellite, and surface characteristics obtained from ground surveys. Flux maps showed the expected close correspondence between greenness, evapotranspiration (ET) and CO2 exchange, but a weaker correspondence between these and ozone flux maps than would be expected if ozone uptake could consistently be scaled to stomatal conductance for moisture or CO2. Examination of the spatial coincidence between transporting structures for the various scalars (heat, moisture, CO2 and ozone), through the Jaccard coefficient of co-location, J, showed a lower overall value (0.45 < J < 0.55) for coincidence in transfer between ozone and moisture than between CO2 and moisture (0.6 < J < 0.7), and analysis of coincidence for the various crop types within the grid permits quantitative assessment of the potential error made when scaling ozone uptake to stomatal conductance. Ln general, the findings suggest the existence of two sinks for ozone only one of which is tied to stomatal conductance, and indicates a possible relative advantage for estimates of ozone uptake based on CO2 rather than moisture exchange.
