This document is the User's Guide to version 3 of the NCAR Community Climate Model, denoted CCM3. It is a companion document to Description of the NCAR Community Climate Model (CCM3) (Kiehl et al., 1996), which describes the governing equations, numerical algorithms, and physical parameterizations used in CCM3. The CCM3 is copyrighted by the University Corporation for Atmospheric Research. This Guide was written with two goals in mind: (1) to provide detailed information that describes how to use CCM3; and (2) to furnish the user interested in modifying the CCM3 code with an in-depth description of the code organization, data structures, and other important details. The form of this report is similar to the User's Guide to NCAR CCM2 (Bath et al., 1992), but has been reorganized and updated to reflect the changes made in creating CCM3. Section II of this report, "Using CCM3", starts by delineating the steps involved in obtaining, compiling and executing CCM3. Next, the namelist input that is used to control a run is described in detail, followed by several examples. The input and output datasets are then discussed, along with a description of the Model printed output and error messages. The section concludes with a brief description of the Slab Ocean Model followed by information on how to get help with the CCM. For the user interested in making changes to CCM3 code, Section III, "CCM3 Internals," has been provided. This section illuminates the basic structure and fundamental features of the CCM3 code. Section IV, "Changing the Model," addresses issues relevant to modifying code, such as the CCM3 coding convention, and includes some specific examples.
