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The University of Southampton
Southampton Marine and Maritime Institute

Recent Advances in Modelling Arctic Sea Ice Seminar

Time:
3:00 - 4:00
Date:
31 October 2012
Venue:
Henry Charnock Lecture Theatre National Oceanography Centre Southampton Visitors should check before travelling to attend the seminar.

For more information regarding this seminar, please telephone Gerard McCarthy on +44 (0) 23 80596175 .

Event details

Arctic sea ice after more than three decades of prolonged thinning and shrinking is now predicted to transform from essentially multiyear ice to essentially (if not entirely) first year ice. With this dramatic evolution comes the necessity to reevaluate all the physical processes that take place in this radically changing system and in particular the driving mechanisms that set the ice in motion and redistribute its mass in and out of the Arctic basin.

Sea ice is subjected primarily to three forces, the atmospheric drag, the oceanic drag and the internal forces in the ice. In the first part of the talk I will introduce some recent results obtained at CPOM concerning the mechanical properties and rheology of sea ice. A new rheology that explicitly accounts for the sub-continuum anisotropy of the sea ice cover has been implemented into the Los Alamos sea ice model (CICE). This is in contrast to all models of sea ice included in GCMs (Global Circulation Models) that use an isotropic rheology. The model contains one new prognostic variable, the local structure tensor, that quantifies the degree of anisotropy of the sea ice, and two parameters that set the time scale of the evolution of this tensor. The anisotropic rheology provides a sub-continuum description of the mechanical behaviour of sea ice and accounts for a continuum scale stress with large shear to compression ratio and tensile stress component. In the second part I will address the momentum transfers between the air and the ice and between the ocean and the ice. Pressure ridges, keels, floe edges and melt pond edges all introduce discrete obstructions to the flow of the air or ocean over the ice, and are a source of form drag. For typical ice covers the form drag contribution to the total drag is of comparable or greater magnitude to the surface or skin drag. Here we combine recent theoretical developments to deduce the total neutral form drag coefficients from the key parameters of the ice cover such as ice concentration, size and area of the ridges and keels, freeboard and floe draft and size of melt ponds. We validate the assumptions of this parameterisation against remote sensing observations from airborne missions (IceBridge) and high resolution satellites. We incorporate the drag coefficients into the sea ice component of a climate model (the CICE model). We present results over the Arctic of a stand-alone version of the model and show the influence of the new anisotropic rheology and the new drag parameterisation on the motion and mass of the ice cover. The impact of this new physics on the Arctic sea ice properties is large and seems to explain some of the differences between models and observations.

Speaker information

Michel Tsamados, UCL, London. Michel Tsamados was appointed as a research associate in the UCL Department of Earth Sciences in January 2010. Michel has a BSc. in Theoretical Physics (statistical and non-linear physics) from Ecole Normale Supérieure de Lyon and a Ph.D. on the mechanical properties and statistical physics of disordered glassy systems awarded in 2009 from Université Claude Bernard Lyon and in collaboration with King's College London. He is also holder of the 'agrégation' in physics, the highest teaching diploma in France.

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