A field methodology to evaluate sonic anemometer angle of attack errors

The inability to consistently close the surface energy balance from independent observations of sensible, latent, ground and storage fluxes has caused micrometeorologists to re-evaluate the methodologies to used to derive the energy fluxes. In particular, the sheltering effect of sonic anemometer transducers is known to distort the flow in a way that can cause the “measured” vertical velocity be less than the true velocity. The error is likely to increase with angle of attack. Algorithms have been derived from observations in made on sonic anemometers in wind tunnels, where flows are generally laminar. In the field, the flow is highly turbulent and the results derived from wind tunnel studies may not necessarily apply. A methodology for evaluating the “angle of attack” error from field measurements is proposed. This methodology requires the use of three identical sonic anemometers, with two being the control and one that can placed in various tilt configurations. Data are presented on showing the angle of attack error, and the impact on the fluxes of sensible heat.