This document is a short description of what GISS ModelE does and gives some references and descriptions of how it does it. Hopefully this will eventually morph into a full technical paper given enough time and resources!
Model development is an ongoing task. As new physics is introduced, old bugs found and new applications developed, the code is almost continually undergoing minor, and sometimes major, reworking. Thus any fixed description of the model is liable to be out of date the day it is printed. Understanding this, we will endeavor to maintain the web version of the document as closely as we can to the current release, however in is inevitable that some discussion here will on occasion fall behind development.
The GISS GCM model development process is over 25 years old (for a very readable description of the historical development see Hansen et al (2000)). Inevitably, decisions that were made and constraints that existed early on in the process have had influences that are still apparent. While much of the subsequent reworking of the model has led to a reduction in these historical influences, some parts of the model still hark back to the days of punch cards, fortran 66 and line printer output. A charitable interpretation would be that while embracing the new (Fortran 90/95, multi-processing, netcdf, etc.), we endeavor to maintain some of the more harmless GISS traditions (which some might call eccentricities) in a spirit of continuity with those who have previously worked on the model. On the other hand, some of those early decisions (for instance regarding diagnostics, or conservation properties) turned out to be very far-sighted and are a principle reason why the GISS series of models continue to play a useful and important role in the world of GCM simulations. We hope that by continuing to make the GISS models a more accessible and better documented, we will be able to carry on in that vein for at least another 25 years.