A Novel Assessment of the Vertical Velocity Correction for Non-orthogonal Sonic Anemometers

Abstract. Non-orthogonal sonic anemometers are used extensively in flux networks and biomicrometeorological research. Previous studies have hypothesized potential underestimation of the vertical velocity turbulent perturbations, necessitating correction to increase flux measurements by approximately 10 %, while some studies have refuted that any correction is needed. Those studies have used cross comparisons between sonic anemometers and numerical simulations. Here we propose a method that yields a correction factor for vertical velocity that requires only a single sonic anemometer in situ but requires some assumptions and adequate fetch at a sufficient distance above roughness elements where surface similarity is valid. Correction factors could be important in adjusting flux network and other flux data, as well as assessing the energy budget closure that is used as one of the flux data quality measures. The correction factor is confirmed in one field experiment and comparison between a CSAT3 and RMY 81000VRE, but it does not work well for the more complex form factors shown in a field comparison of an IRGAson and a CSAT3a.