1 Introduction

The Community Climate System Model (CCSM) is a coupled climate model consisting of atmosphere, ocean, land, and sea ice components which exchange fluxes and states through a coupler. This model is making important contributions to knowledge about past, present, and future climates.

The sea ice component of CCSM Version 2 is the Community Sea Ice Model Version 4, or CSIM4. The physics of this component is described in (Briegleb et al.(2002)). Accessing and running CSIM4 is described in (Schramm(2002)). This document discusses the CSIM4 source code, its general organization and data structures, a detailed listing of all modules (including subroutines, module reference and input/output arguments), how to add new fields to the history file, and finally suggestions on modifying the source code.