Surface Turbulent Exchange over the Arctic Ocean—Measurements from the SWERUS-C3 / ACSE Project (Invited Presentation)

Direct measurements of turbulent fluxes over sea ice are challenging to obtain due to the remote location and often harsh conditions, and parameterizations within large scale models perform poorly in comparison to those over land or the open ocean. In fractional ice conditions the mix of open water and ice surfaces on a range of spatial scales and damping of waves by floating ice complicates the exchange processes.

Here we present a first look at measurements made during a 3-month cruise of the icebreaker Oden within the Arctic Ocean during the summer and early autumn of 2014. Eddy covariance measurements are made from a specially installed mast over the bow of the Oden; these include the fluxes of momentum, heat, water vapour, and methane. The superstructure of the Oden will distort the mean flow of air over it, causing streamlines to lift and the flow to change speed. Corrections for these effects are determined through CFD modelling of the air flow around the ship; Doppler lidar measurements of the mean wind profile upstream of the ship are used to validate the CFD model results. Regional ice fraction is estimated from daily satellite retrievals, and the immediate local ice fraction estimated from digital imagery obtained from cameras mounted above the ship's bridge. Boundary layer thermodynamic and dynamic structure are derived from measurements from the Doppler lidar, a scanning microwave radiometer, Doppler cloud radar, and a radar wind profiler. The lidars, radiometer, and cloud radar are all stabilised against the changing pitch and roll of the ship, and the residual linear motions are measured in order to correct the Doppler wind measurements. When on station a waverider buoy will be deployed to measure 2D wave spectra whenever ice conditions permit, allowing the impact of fractional ice damping of wind-driven waves to be assessed.

Measurements will be made in a wide variety of conditions – from open ocean through marginal sea ice and into the pack ice; and during the peak of the summer melt into the early autumn freeze up.