Sensitivity studies on vortex development over a polynya |
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Authors: | H Hebbinghaus H Schlünzen S Dierer |
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Institution: | Meteorologisches Institut, ZMK, Universit?t Hamburg, Hamburg, Germany Meteorologisches Institut der Universit?t Bonn, Bonn, Germany MeteoSchweiz, Zürich, Switzerland
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Abstract: | Summary The development of a cyclonic vortex over a polynya is investigated with the primitive equation mesoscale model METRAS. The
impact of different atmospheric processes on vortex development is determined by calculating the terms of the vorticity tendency
equation. Sensitivity studies are performed for different large-scale situations (geostrophic winds 1 ms−1, 3 ms−1, 20 ms−1, initial ice-water temperature difference of 35 K or 17.5 K) and for different polynya sizes and shapes. In general, the
vortex develops within a few hours. It is intensified by buoyancy, mainly resulting from latent heat release. Advective and
diffusive processes hinder the vortex development. The intensification depends on the actual situation and is faster over
small polynyas and heterogeneous ice cover. These situations result in intensification periods of only 12 to 18 hours for
the vortex, but create very strong vortices. Halved horizontal temperature gradients also about halve the vortex intensity.
The lifetime and intensification of a vortex increases with the time the air mass spends over the water. Thus, weak winds
show a slower development of the vortex but the vortex intensifies for more than 24 hours. Over big polynyas several vortices
develop, a long polynya results in a longer and narrower vortex which intensifies over a longer period. |
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