Impact of Motion Correction on Momentum and Sensible Heat Fluxes over Ice and Water Measured on a Moving Vessel in the Arctic

The Arctic exhibits an alarming warming rate, mainly caused by increasing greenhouse gas emissions and the climate forcing effect of aerosols. To get a better understanding of the relevance of local aerosol sources and sinks in the Arctic, vertical near-surface particle, momentum and sensible heat fluxes were investigated by collecting a large eddy covariance data set including three-dimensional wind speed, temperature and particle number concentration over ice, water and mixtures thereof during the PS131 expedition of the German research icebreaker Polarstern in 2022 using a 3-axis ultrasonic anemometer (Gill Solent HS-044, Lymington, United Kingdom) and a mixing condensation particle counter (Brechtel Model 1720, Hayward, USA). Both instruments were installed on the bow crane outrigger.

To minimize the influence of the inadvertent movement of the vessel caused by waves and wind on the anemometer data, two separate motion correction approaches were tested. The first method is based on the work of Fujitani (1981) and Edson et al. (1998). It realigns the wind vector (u, v, w) recorded in the vessel coordinate system with a reference frame while also correcting for apparent winds resulting from the tilting motion and the vessel movement in the reference coordinate system itself. Alternatively, by making use of the periodicity of the vessel movement and finding the frequencies with which the vertical wind vector component w oscillates using spectral FFT analysis, affected frequencies can be replaced assuming spectral similarity of atmospheric turbulence. Thus, it is possible to remove the impact of the movement without having to rely on the measured pitch, roll and yaw angles.

Both approaches were successfully used to correct the recorded data in preparation for calculating the sensible heat and momentum fluxes. Preliminary results suggest that the choice of motion correction approach has an impact on the obtained fluxes, though a complete evaluation of the resulting data is still pending at the time of abstract submission.

This study was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation): HE5214/10-1, HE5214/11-1 and WE 2757/6-1.