# Dealing with more difficult modeling choices¶

Most uses of an ice sheet model depend on careful modeling choices in situations where there are considerable uncertainties and the model results depend strongly on those choices. There may be, at the present state of knowledge, no clear default values that PISM can provide. Furthermore, the available PISM options and sub-models are known to not be sufficient for all users. Thus there are modelling situations for which we know the user may have to do a great deal more hard work than just choose among PISM runtime options.

Here are example cases where users have worked hard:

• User made use of available data in order to choose parameters for existing PISM models. These parameters then override PISM defaults.

Example

Use regional atmosphere model output to identify PDD parameters suitable for modeling surface mass balance on a particular ice sheet. Then supply these parameters to PISM by a -config_override file.

• User wrote code, including code which modified current PISM internals, either to add additional processes or to “correct” PISM default process models.

Example

Add a new sub-ice-shelf melt model by modifying C++ code in the src/coupler/ directory.

• User simplified the model in use, instead of the default which was more elaborate.

Example

Instead of using the PISM default mechanism connecting basal melt rate and basal strength, bypass this mechanism by generating a map of yield stress tauc directly and supplying it as input.

 Previous Up Next