Measurement of momentum and heat flux variations in the surface boundary layer

Recent measurements of momentum and heat flux between 5.66 and 22.6 meters on a tower over a flat uniform site indicate that both fluxes are constant with height to within ±20%. Some important aspects of instrument performance relevant to flux measurement, e.g., sonic anemometer array configuration, alignment and leveling of the axes, and errors in sonic thermometry, are discussed. The large variations observed in the vertical momentum flux gradient during unstable conditions appear to be the result of intermittent bursts in the momentum transport. Some characteristics of these bursts are described. Long averaging periods, of the order of an hour, are needed for meaningful estimates of flux gradients under such conditions.