Jet formation at the sea ice edge
Harold Heorton (PhD student), Daniel Feltham, Ann Keen (CASE supervisor at UK Meteorological Office)
Jet formation is well understood over coastlines. The jets form due to the Coriolis effect upon a flow over a sharp change in surface roughness which is present between the relatively smooth ocean and rough land. The jet is in the form of a band of increased velocity about the change in surface roughness.
See Figure. For winds or ocean currents travelling from the open ocean to the sea ice pack (1), the sea ice edge will be compacted and have a rapidly increasing sea ice concentration (2). This gives a sharp change in surface roughness at the ice/ocean boundary (3). This perturbs the wind or current parallel to the edge. This perturbation is greatest at the ice edge (4), decaying away over a Rossby radius, (e.g. 75 km for the atmosphere, 6 km for the ocean). The addition of this jet to the wind and ocean results in the formation of an ice jet of similar width (5). The non-dimensionalised velocity enhancements of the applied jets and resultant ice jet are of similar magnitude.
The jet formation has been modelled using a simple idealised model. This model is one dimensional and solves the momentum balance of the sea ice – ocean mixture layer. The jets have also been introduced into the sea ice component of a climate model, the CICE model. The introduction of the ice edge jets into this model will be used to show their effect upon sea ice extent.