Spectral Effects on Scalar Correlations and Fluxes

A field experiment designed to test sensor separation effects by means of multiple thermocouple measurements co-located with a sonic anemometer, a fast gas analyzer and a slow set of CO2 and humidity sensors is described. The data allowed the experimental determination of decorrelation between scalars, both because of instrumental effects (mostly sensor separation) and physical ones (mostly large-scale ABL processes associated with flux entrainment at the top). The large-scale effects are more important in terms of the decorrelation they produce, and yet their effect on the measured fluxes is not too large, on account of the high-pass filtering nature of the multiplication by the vertical velocity fluctuation, with its inherently higher-frequency range.