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SUMMARY:Modeling Land-Ice Retreat\, Ice-Ocean Interactions and Sea-Level R
 ise in the Community Earth System Model - William Lipscomb\, Los Alamos Na
 tional Laboratory and Xylar Asay-Davis\,  New York University\, Potsdam In
 stitute for Climate Impact Research\,  Los Alamos National Laboratory
DTSTART:20130925T143000Z
DTEND:20130925T153000Z
UID:TALK47449@talks.cam.ac.uk
CONTACT:Rosie Williams
DESCRIPTION:The Earth’s ice sheets and glaciers are retreating and raisi
 ng global sea level. Century-scale sea-level projections are uncertain and
  controversial\, with discrepancies between semi-empirical approaches and 
 physically based models. We are beginning to use a global climate model\, 
 the Community Earth System Model (CESM)\, to simulate land-ice retreat and
  sea-level rise. Version 1 of CESM includes a dynamic ice sheet model\, th
 e Glimmer Community Ice Sheet Model (Glimmer-CISM). The ice sheet model is
  forced by a surface mass balance (SMB) computed in multiple elevation cla
 sses in CESM's land model and downscaled to the ice sheet grid. For most o
 f the Greenland ice sheet\, CESM generates an SMB in good agreement with o
 bservations and regional climate models. Members of the CESM Land Ice Work
 ing Group are now working to (1) improve Glimmer-CISM by including higher-
 order ice-flow dynamics and more realistic physical parameterizations\, (2
 ) simulate the evolution of small glaciers and ice caps\, (3) implement tw
 o-way coupling between the ice sheet and land models\, with land surface t
 ypes that change over time\, and (4) incorporate ice-sheet/ocean coupling 
 beneath ice shelves. \n\nIn the second half of the talk we focus on this l
 ast area of research.  Fully coupled ice-sheet/ocean interactions involve 
 dynamic boundaries between model components\, a prospect that was not inco
 rporated in CESM's design (or that of other Earth System Models).  We are 
 making rapid progress in bridging this gap.  Recently\, we have added the 
 ability to simulate static sub-ice-shelf cavities into CESM's ocean model\
 , the Parallel Ocean Program (POP).  We are now in the process of validati
 ng the model under present-day conditions.  We are also performing a serie
 s of idealized ice-sheet/ocean simulations that are coupled offline (async
 hronously)—each model is run for a coupling time step based on boundary 
 conditions from the other model's previous time step.  Building on our exp
 erience with offline coupling\, we are in the early stages of implementing
  dynamic boundaries in both POP and the CESM coupler.\n
LOCATION:British Antarctic Survey\, Room 187
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