Energy and ozone fluxes over sea ice

We present surface layer measurements made over Hudson Bay seaice during February/March 2008 from the COBRA (Impact of combined iodine and bromine release on the Arctic atmosphere) experiment which formed part of the International OASIS (Ocean-Atmosphere-SeaIce-Snowpack) IPY programme. All components of the local surface energy balance were measured and it was defined by net radiative cooling throughout most of the day, mainly balanced by the conductive heat flux from the warmer sea water to the cooler seaice at the surface, and a small net radiative warming for a few hours after midday. Unique ground-level ozonefluxes were measured by eddy covariance and deposition velocities ranged from +0.5 mm s−1 (deposition) to −1.5 mm s−1 (emission). Ozone profile measurements suggested ozoneflux divergence within the surface layer. The observed bi-directional fluxes and flux divergence with height reveal the complexity of surface ozonefluxes in the Arctic spring time surface layer, and show that ozone exchange with the seaice surface is best probed using the eddy covariance method alongside frequent or continuous profile measurements. In this study, the local in-situ ozone-halogen photochemistry was identified as weakly controlling the measured ozoneflux, whereas horizontal advection and vertical mixing were considered more important in influencing fluxes. Under these conditions, several measurement sites would be desirable in order to quantify the contribution of advection to the local surface exchange.

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