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SUMMARY:Inferring the subsurface flow of Antarctic ice from satellite obse
 rvations and other challenges for ice sheet prediction - Robert Arthern (B
 AS)
DTSTART:20131015T120000Z
DTEND:20131015T130000Z
UID:TALK48077@talks.cam.ac.uk
CONTACT:Doris Allen
DESCRIPTION:Nowadays there are a large number of satellite and airborne ob
 servations of the large ice sheet that covers Antarctica. These include ma
 ps of the surface elevation\, ice thickness\, surface velocity\, the rate 
 of snow accumulation\, and the rate of change of surface elevation. Uncert
 ainty in the possible rate of future sea level rise motivates using all of
  these observations and models of ice-sheet flow to project how the ice sh
 eet will behave in future\, but this is still a challenge. To make useful 
 predictions\, especially in the presence of potential dynamic instabilitie
 s\, models will need accurate initial conditions\, including flow velocity
  throughout the ice thickness. The ice sheet can be several kilometres thi
 ck\, but most of the observations identify quantities at the upper surface
  of the ice sheet\, not within its bulk. There is thus a question of how t
 he subsurface flow can be inferred from surface observations. The key para
 meters that must be identified are the viscosity in the interior of the ic
 e and the basal drag coefficient that relates the speed of sliding at the 
 base of the ice sheet to the basal shear stress. Neither is characterised 
 well by field or laboratory studies\, but for incompressible flow governed
  by the Stokes equations they can be investigated by inverse methods analo
 gous to those used in electric impedance tomography (which is governed by 
 the Laplace equation). Similar methods can also be applied to recently dev
 eloped 'hybrid' approximations to Stokes flow that are designed to model s
 hallow ice sheets\, fast-sliding ice streams\, and floating ice shelves mo
 re efficiently. This talk will give a summary of progress towards model ba
 sed projections of the size and shape of the Antarctic ice sheet that make
  use of the available satellite data. Some of the outstanding problems tha
 t will need to be tackled to improve the accuracy of these projections wil
 l also be discussed.
LOCATION:CMS\, MR15
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