[issm-support] palaeo ice sheet modelling

[Morlighem, Mathieu (334H-Affiliate)]

Hi Henry,

thank you for your interest in ISSM. We have never used ISSM for long paleo runs but there should not be any major problem. Nevertheless, you should be aware of a few limitations:
1. The boundaries are not moving (fixed ice front). So you cannot start from an ice-free model. You can start with a thickness of 10 m everywhere and let the model evolve, assuming that the position of the front will not change.
2. There is no PDD implemented in ISSM: if you use a 2d model, you must provide a time series of surface mass balance, if you have a 3d model and also compute the thermal regime, you will need a surface temperature time series as well to force the model.

If you want to apply a forcing that varies with time, say the surface mass balance, instead of providing a vector of size "md.mesh.numberofvertices", you must provide a matrix of size [md.mesh.numberofvertices+1    " number of time series"], where the last row is the time for each vector. for example, if you have the vectors smb1, smb2,... smbN interpolated on the mesh for times: time1, time2,...timeN (in years), the forcing should be imposed as:

md.surfaceforcings.mass_balance =[ [smb1; time1],  [smb2; time2], ... [smbN; timeN]];

For a given time step in the transient run, the model will interpolate the smb linearly between the two closest years provided.
If you are interested in developing a more sophisticated surface mass balance module based on surface temperatures, we can help you.

Thanks,
Mathieu

On Mar 19, 2012, at 9:58 AM, Henry Patton wrote:

Hi,

I have a rather basic question regarding modelling of palaeo ice sheets with the ISSM The model has been installed and have gone through the tutorials available…everything seems to be working great which is good news.

It seems relatively straightforward to start modelling projections of current ice sheets like Greenland/Antarctica, for example setting initial values of smb then making simple transient forcings, but if I wanted to say reconstruct an ice sheet starting from an ice-free topography, is it possible for the model to calculate mass balance from a prescribed temperature forcing curve e.g. from an ice core record. Looking through the model’s parameters it doesn’t seem obvious to me, but I may be missing something.

Thanks,
Henry
----------------------------------------------
Henry Patton

Centre for Glaciology
H6, Institute of Geography and Earth Sciences,
Aberystwyth University,
Ceredigion,
SY23 3DB

Tel: 01970 621859
Fax: 01970 622659

research.henrypatton.org<http://research.henrypatton.org/>


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Mathieu Morlighem
Assistant Project Scientist
Department of Earth System Science
University of California, Irvine

(818) 354-4134 (office)
(626) 429-5780 (cell)
Mathieu.Morlighem at uci.edu<mailto:Mathieu.Morlighem at uci.edu>
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