ERRORS IN AIRBORNE FLUX MEASUREMENTS

We present a general approach for estimating systematic and random err ors in eddy correlation fluxes and flux gradients measured by aircraft in the convective boundary layer as a function of the length of the f light leg, or of the cutoff wavelength of a highpass filter. The estim ates are obtained from empirical expressions for various length scales in the convective boundary layer and they are experimentally verified using data from the First ISLSCP (International Satellite Land Surfac e Climatology Experiment) Field Experiment (FIFE), the Air Mass Transf ormation Experiment (AMTEX), and the Electra Radome Experiment (ELDOME ). We show that the systematic flux and flux gradient errors can be im portant if fluxes are calculated from a set of several short flight le gs or if the vertical velocity and scalar time series are high-pass fi ltered. While the systematic error of the flux is usually negative, th at of the flux gradient can change sign. For example, for temperature flux divergence the systematic error changes from negative to positive about a quarter of the way up in the convective boundary layer.