Accuracy of Wind Observations from Open-Ocean Buoys: Correction for Flow Distortion

Abstract

The comparison of equivalent neutral winds obtained from (i) four WHOI buoys in the subtropics and (ii) scatterometer estimates at those locations reveals a root-mean-square (RMS) difference of 0.56–0.76 m s−1. To investigate this RMS difference, different buoy wind error sources were examined. These buoys are particularly well suited to examine two important sources of buoy wind errors because 1) redundant anemometers and a comparison with numerical flow simulations allow us to quantitatively assess flow distortion errors, and 2) 1-min sampling at the buoys allows us to examine the sensitivity of buoy temporal sampling/averaging in the buoy–scatterometer comparisons. The interanemometer difference varies as a function of wind direction relative to the buoy wind vane and is consistent with the effects of flow distortion expected based on numerical flow simulations. Comparison between the anemometers and scatterometer winds supports the interpretation that the interanemometer disagreement, which can be up to 5% of the wind speed, is due to flow distortion. These insights motivate an empirical correction to the individual anemometer records and subsequent comparison with scatterometer estimates show good agreement.

The Annual Cycle of Air-Sea Fluxes in the Northwest Tropical Atlantic

“…Schlundt et al (2020) compared satellite and ASIMET wind measurements from other Ocean Reference Stations in the trade winds regions, including NTAS, and observed that wind speed discrepancies were less than 5% and consistent with flow distortion from CFD simulations (Emond et al, 2012). An empirical correction to the flow distortion exists that reduces the wind speed error to 5% of the true wind (Bigorre et al, 2013;Schlundt et al, 2020). This correction was not implemented here, as the flow distortion and platform motion errors are small at NTAS and do not impact our conclusions.…”

“…Using data from a mooring deployed in the Gulf Stream, where high winds and currents induced significant platform motion and tilt, Bigorre et al (2013) showed that the total wind speed error could reach up to 10% of the true wind in these extreme conditions. Schlundt et al (2020) compared satellite and ASIMET wind measurements from other Ocean Reference Stations in the trade winds regions, including NTAS, and observed that wind speed discrepancies were less than 5% and consistent with flow distortion from CFD simulations (Emond et al, 2012). An empirical correction to the flow distortion exists that reduces the wind speed error to 5% of the true wind (Bigorre et al, 2013;Schlundt et al, 2020).…”

“…The accuracy of the ASIMET data has been characterized using comparisons with measurements from ships, fixed platforms and satellites (Colbo and Weller, 2009;Bigorre et al, 2013;Weller, 2018;Schlundt et al, 2020), as well as Computational Fluid Dynamics simulations (Emond et al, 2012). Colbo and Weller, 2009 describe the accuracy of ASIMET measurements at NTAS and from similar moorings in trade winds regions.…”

Ocean and Atmospheric Observations at the Remote Ieodo Ocean Research Station in the Northern East China Sea

“…Forth and post-construction, the effects of the ORS structure on oceanic and atmospheric conditions must be measured to evaluate the reliability, representativeness, and quality of the ORS data. This evaluation step can limit platform derived errors leading to measurement bias, something that is of particular concern when seeking to produce long-term regionally representative monitoring records (Schlundt et al, 2020).…”

“…Note that, as with platform related wind distortion (Schlundt et al, 2020), large structures can distort ocean currents in their vicinity, leading to a measurement bias. This effect may, in turn, affect ocean properties locally (e.g., temperature and salinity) such that careful seasonal comparisons between Ieodo ORS and the ambient area are required to identify whether these observations are representative, without substantive distortion.…”