A brief note to users ...
The Community Earth System model (CESM) and its predecessor, the Community Climate System Model (CCSM) and their component models have been invaluable tools for the national and international research communities. These models have been used by researchers worldwide, starting with the first version CSM1, to explore problems of both greenhouse and icehouse past climates. They have been shown to be adaptable for both deep-time paleoclimate applications, when the continental configurations were much different from present, to the more near-term past climates of the glacial-interglacial cycles of the last million years. Over 60 research articles using versions of CCSM for studying past climates have been published by the community. Low-resolution versions of CCSM have been developed and supported to allow paleoclimate researchers to integrate the model for thousands and even tens of thousands of years. This technical note outlines the procedures for setting up paleoclimate simulations with CCSM3, the version of CCSM released in 2004. The science of the paleoclimate simulation still rests on the researcher. Choices will need to be made on the appropriate conditions (i.e., land-ocean configuration, topography and bathymetry, ice sheets, vegetation) for the specific paleoclimate research topic being explored. Additional information on the component models and options that may need to be set can be found in the technical notes of these models. We thank all those who have contributed their time and expertise for maintaining the paleoclimate versions of CCSM.
Bette Otto-Bliesner and Jeff Kiehl
This document describes the procedures for creating a CCSM3 paleoclimate simulation in the fully coupled (all active components) configuration. We provide tools and examples of the process used to create paleoclimate simulations using the computing resources at the National Center for Atmospheric Research (NCAR). This document is to be used as a guide; researchers are ultimately responsible for modifying the process to accommodate their time period of interest as well as adapting the tools to their available computer resources.
Throughout this User’s Guide we differentiate between the procedures required to create (1) near-modern (e.g., Quaternary, Pliocene) or (2) Deep-Time (pre-Quaternary) model simulations. In near-modern simulations, the continents are in their present-day positions, and the land/sea masks do not require significant modification. Quaternary modelers are often able to use existing forcing files to simulate past climate. By contrast, deep-time simulations require drastic modifications to the land/sea mask, and the modeler is responsible for providing the orographic/bathymetric maps for their geologic period of interest.
This document assumes a default fully coupled CCSM3 configuration. We do not describe the creation of the forcing files used in Data Model components or in stand-alone component model runs. To gain more understanding about the CCSM3 component models and input files, see the CCSM3 documentation (http://www.cesm.ucar.edu/models/ccsm3.0/), and refer to the Appendices in this document for links to CCSM3 User guides and useful model set-up tools.
The CCSM3 paleoclimate liaisons are available for consultation. Please see the CCSM3 webpage for contact details. (http://www2.cesm.ucar.edu/working-groups/pwg).