FLUX ESTIMATES OF LATENT AND SENSIBLE HEAT, CARBON-DIOXIDE, AND OZONEUSING AN AIRCRAFT-TOWER COMBINATION

Several recent large-scale experiments in land-surface climatology hav e used the combination of aircraft- and tower-based flux measurements. Within these experiments, much effort has been made to assess the pot ential of aircraft to serve as extended observation platforms for the scaling up from local (tower-based) to regional estimates of surface-a tmosphere exchange. Data collected as part of the California Ozone Dep osition Experiment (CODE), during a one-month period of consistent day -to-day wind and radiation conditions, were particularly conducive to such a study. Aircraft-based flux estimates obtained at 30 and 60 m ab ove two vineyard sites of approximately 9 km(2) (site A, 6 km x 1.5 km and site B, 4.5 km x 2 km) were compared to tower-based measurements made at 9.4 m above a section of site A. This paper shows that over th e measuring period the sum of sensible and latent heat Bur at 30 m, as measured with the aircraft-based system, was about 11% less than that measured with a tower-based system at 9.4 m. It also shows that fluxe s at 30 m were on the average about 10% larger than those at 60 m. It documents the flux variability of CO2, sensible and latent heat and oz one observed over relatively homogeneous surfaces. Although aircraft-t ower comparisons must be interpreted with caution, due to the dissimil ar surface areas sampled by the stationary and moving sensors located at different elevations, the consistent relationship obtained between these two sampling systems demonstrates the complementary nature of su ch measurements. It confirms that very repeatable measurements can be obtained with aircraft-based systems over distances as short as a few kilometers. It also demonstrates that compositing data for several run s and for several days from aircraft- and tower-based measurements can provide diurnal patterns of fluxes of sensible and latent heat as wel l as CO2 and O-3 on a regional scale.