Abstract

The method of elevation classes has proven to be a useful way for a low-resolution GCM to produce high-resolution downscaled surface mass balance fields, for use in one-way studies coupling GCMs and ice flow models. However, past uses of elevation classes have been a cause of non-conservation of mass and energy, causing problems for potential two-way coupling.

We present a generalization of the method of elevation classes that conserves mass and energy fluxes. We identify three grids between which data must be regridded, and five transformations between those grids required by a typical coupled GCM / ice flow model. We show how each of those five transformations may be implemented in a conservative manner. Confounding real-world issues are discussed, including the use of projections for ice modeling, how to handle dynamically changing ice geometry, and modifications required for finite element ice models.

We have implemented these transformations in GLINT2 , a library used to couple GCMs with ice models. Source code and documentation are available for download.