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Title: The interaction between climate and ice sheets : with special reference to the boundary layer of the ablation zone
Author: Hall, Alison
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1992
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Investigations of the interaction between climate and ice sheets were originally based on the orbital theory of the ice ages, and arose through a desire to understand the glacial cycles. More recently, interest has been stimulated in this field, with concern of global warming and the role of ice sheets with respect to future climatic change. The work of glaciologists shows that ice sheet models are very sensitive to the climate of the ablation zone. Studies by climatologists tend to look at the larger scale climate, concentrating on accumulation, rather than ablation patterns. This work looks at the way in which climate models can be used to simulate the climate over an ice sheet, in order to assess the climatic variables most sensitive to ice sheet evolution. Data of the climate over the present day ice sheets in Antarctica and Greenland have been compiled and presented in a form suitable for comparison with GCM data. The work shows that GCM's cannot reproduce the temperature field, and boundary layer structure sufficiently accurately to provide boundary conditions for an ice sheet model. A slab model is developed and used over the glacial slopes to investigate the way in which the boundary layer may affect the ablation of the ice. Over the glacial slopes, the boundary layer flow is turbulent and characterised by entrainment of warm air from above. The rate of entrainment governs the depth, temperature and wind regime of the boundary layer. Two new types of entrainment parameterisation are investigated, and compared to the laboratory derived formulation of Ellison &38 Turner (1959). Experiments show that the method of parameterisation of entrainment is not important, although the coefficients derived in the laboratory tend to be too high; this suggests that there is more loss of TKE from the boundary layer on the glacial slopes, than empirical data from the laboratory suggests. The model is run using surface profiles from present ice sheets, as well as reconstructed profiles from the Laurentide ice sheet at the last glacial maximum. The model is used to look at the climatic parameters which influence the ablation of ice, as well as the way in which the ice sheet itself may influence the climate of the boundary layer. Conclusions show that the evolution of ice depends on a balance between the upper geostrophic wind, the boundary layer development, ice sheet shape and surface radiation budget. If an ice sheet steepens as it retreats, the air accelerates, producing a warmer boundary layer via entrainment. This will enhance the steepening process, and increase the rate of retreat of the ice.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available