Articles | Volume 15, issue 18
Atmos. Chem. Phys., 15, 10619–10629, 2015
https://doi.org/10.5194/acp-15-10619-2015
Atmos. Chem. Phys., 15, 10619–10629, 2015
https://doi.org/10.5194/acp-15-10619-2015

Research article 25 Sep 2015

Research article | 25 Sep 2015

Motion-correlated flow distortion and wave-induced biases in air–sea flux measurements from ships

J. Prytherch1, M. J. Yelland2, I. M. Brooks1, D. J. Tupman1,a, R. W. Pascal2, B. I. Moat2, and S. J. Norris1 J. Prytherch et al.
  • 1School of Earth and Environment, University of Leeds, Leeds, UK
  • 2National Oceanography Centre, Southampton, UK
  • anow at: Centre for Applied Geosciences, University of Tübingen, Germany

Abstract. Direct measurements of the turbulent air–sea fluxes of momentum, heat, moisture and gases are often made using sensors mounted on ships. Ship-based turbulent wind measurements are corrected for platform motion using well established techniques, but biases at scales associated with wave and platform motion are often still apparent in the flux measurements. It has been uncertain whether this signal is due to time-varying distortion of the air flow over the platform or to wind–wave interactions impacting the turbulence. Methods for removing such motion-scale biases from scalar measurements have previously been published but their application to momentum flux measurements remains controversial. Here we show that the measured motion-scale bias has a dependence on the horizontal ship velocity and that a correction for it reduces the dependence of the measured momentum flux on the orientation of the ship to the wind. We conclude that the bias is due to experimental error and that time-varying motion-dependent flow distortion is the likely source.

Download
Short summary
Signals at scales associated with wave and platform motion are often apparent in ship-based turbulent flux measurements, but it has been uncertain whether this is due to measurement error or to wind-wave interactions. We show that the signal has a dependence on horizontal ship velocity and that removing the signal reduces the dependence of the momentum flux on the orientation of the ship to the wind. We conclude that the signal is a bias due to time-varying motion-dependent flow distortion.
Altmetrics
Final-revised paper
Preprint