The correspondence of aircraft-measured fluxes of sensible heat, latent heat, CO2 and ozone to the surface characteristics in the San Joaquin Valley of California

Fluxes of sensible heat, latent heat, CO2 and ozone over a variety of land surfaces, based on 5 km-averaged near-surface airborne data, are examined within the 1991 California Ozone Deposition Experiment (CODE) in the San Joaquin Valley of California. It is found that the fluxes of sensible heat, latent heat and CO2 are well correlated and correspond significantly to the surface greenness index over all selected surface types, which indicates that the three fluxes are primarily driven by the surface biological (physiological) processes. However, a significant correspondence between ozone flux and the surface greenness index is found only over the vegetative surfaces. The nonvegetative surfaces are composed of recently-cultivated bare soil and newly-cut hay, where the rapid chemical reactions of ozone with its precursors originating from soil microbial activities might become an important controlling factor. This suggests that ozone flux may be controlled by a combination of the surface uptake process dominant over the vegetative surfaces and the atmospheric chemical process dominant over the nonvegetative surfaces. The two kinds of processes may mask each otherʹs effects, and lead to the poor and confusing correspondence between ozone flux and the surface greenness index.