Momentum exchange between atmosphere, sea ice and ocean

  • The Arctic is experiencing ongoing dramatic changes. The strongest evidence of these changes is in the sea ice. The ice cover showed a reduction in areal extent and total volume. Older ice is giving space to new and thinner ice, and large surface topographic elements are disappearing accompanied by an increase of melt ponds and smaller topographic features. Moreover, the sea ice, which is not a stationary cover but moves in response to external forcing, showed an increase in drift speed over the last 30 years. The ice is coupled to the ocean and the atmosphere by exchanging heat and momentum, thus changes in sea ice may affect the other two components through mechanisms that are not fully understood yet. In the light of these recent changes, a good understanding of the factors determining the lifetime, movement and evolution of the ice is becoming necessary, together with a proper investigation of the coupling of sea ice with atmosphere and ocean. It is known that the intensity of the atmosphere-ice and ocean-ice interactions depend on the roughness of the separation interface; the roughness of the ice surface is determined by the concentration and shape of the topographic elements. The aim of this thesis is to estimate the momentum fluxes over the entire Arctic Basin as function of sea-ice topography. The present study splits in two parts: as first the momentum fluxes between atmosphere and ice and between ice and ocean are estimated based on real topography data. Then the results are upscaled with numerical simulations. This second step allows also to evaluate the impact of a more detailed physical description of the atmosphere-ice-ocean interactions on the ocean circulation. The study based on sea-ice topography data showed a high variability in space and time of the ice surface, such variability is then reflected in the momentum fluxes. The concentration of large and small topographic elements differs from region to region according to the age of ice and to the deformation history. In particular, this study revealed that considering only the large topographic elements is not enough to characterize the degree of deformation of an ice field and thus to evaluate the strength of the air-ice-ocean interactions. The model study showed that by introducing a topography dependent description of the atmosphere-ice-ocean interaction, the sea ice is affected in its thickness, areal extent and drift. Moreover, changes in the ice topography affect the ocean to a large extent: the ocean shows changes not only in the surface circulation, but also in the circulation of the deeper Atlantic water. This reveals that in order to obtain correct predictions for the future of the Arctic a better description of subgrid processes, like the formation of surface roughness elements and their impact on the drag coefficients, is needed.

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Publishing Institution:IRC-Library, Information Resource Center der Jacobs University Bremen
Granting Institution:Jacobs Univ.
Author:Giulia Castellani
Referee:Rüdiger Gerdes, Michael Bau, Martin Losch, Christof Lüpkes
Advisor:Rüdiger Gerdes
Persistent Identifier (URN):urn:nbn:de:gbv:579-opus-1000002
Document Type:PhD Thesis
Date of Successful Oral Defense:2014/11/13
Year of Completion:2014
Date of First Publication:2015/10/22
PhD Degree:Geosciences
School:SES School of Engineering and Science
Library of Congress Classification:G Geography. Anthropology. Recreation / GC Oceanography / GC190-190.5 Ocean-atmosphere interaction
Call No:Thesis 2014/64

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