Version 6.0 of the CCSM Coupler, cpl6, is included with version 3 of the Community Climate System Model. The name ``cpl6'' is meant to reflect its place in the lineage of CCSM couplers but cpl6 is very different from its predecessors. Like cpl5 and earlier versions, cpl6 includes a specific instance of a coupler main program to implement CCSM3's coupling scheme. But new with this version, cpl6 also includes a class library of Fortran90 modules which provide a flexible and uniform way to construct the Coupler main program and interface it to the other components of CCSM. Along with more flexibility, cpl6 allows the Coupler to be run as a distributed memory parallel application.
This guide is divided into three parts. Part I is the traditional User's Guide and describes how to use the Coupler main included within CCSM3, modify its runtime options, and understand its output. Part II, the Source Code Reference, describes the structure of the Coupler main and also describes the objects and methods of cpl6 and how to use them to modify or construct a new coupled system. Part III contains the scientific description of the Coupler including details on the physical calculations performed in the Coupler.