The NCAR Community Climate Model version 3.6 (CCM3.6) is now released.

CCM3.6 is the latest version of the NCAR Community Climate Model. It is in the same family as CCM3.0 and therefore most of the code is the same with only minor changes to the physical parameterizations. The simulated climate of CCM3.6 does not differ significantly from that of CCM3.2.

The CCM3.6 is a stable, efficient, documented, state of the art, atmospheric general circulation model designed for climate research on high-speed supercomputers and select upper-end workstations.

CCM3.6 is released as a free resource to scientists and graduate students worldwide as an advanced tool for global atmospheric modeling research, allowing them to develop and implement their particular area of modeling expertise without spending decades of their careers building a complex global climate model.

The CCM3.6 source code, initial and boundary datasets, documentation, model verification and control simulations may be downloaded from the CCM3 home page at http://www.cgd.ucar.edu/cms/ccm3 .

The National Center for Atmospheric Research is operated by the University Corporation for Atmospheric Research and is sponsored by the National Science Foundation.

Modifications (to CCM3.2) include:

Physics changes (no significant change to the climate):

• Added capability to calculate earth's orbital parameters.
• Changed algorithm to calculate solar zenith angle.
• Modified surface stress calculation.
• Solar radiation calculations now include 19 bands. This allows comparison to Nimbus-7 spectral albedos.
• 2m-reference height temperature computed everywhere, both in flux-coupled mode and stand-alone mode.
• Snow capped to 1m over land ice.
• Negative runoff in LSM is allowed for glaciers, lakes, wetland, and irrigated land so that the model conserved water globally.

Changes to input/output files:

• The ozone dataset is now interpolated horizontally and vertically during the model run.
• All input files are now netCDF format rather than ccm history file
• LSM and CCM generate initial conditions files during model runs.
• Input and output LSM datasets are in netCDF format.
• LSM can now generate its own initial dataset at model startup.
• Off-line programs interpic, and definesurf are now provided to interpolate initial conditions to a different resolution.
• An off-line program interpsst is now privided to interpolate Sea Surface Temperature (SST) data to a different resolution.

Changes to user interface:

• Added capabilities to run model adiabatically or with prescribed heating.
• Solar constant added as a namelist input variable.
• Volume mixing ratios for greenhouse gases added as namelist input.
• Output primary history files and restart datasets renamed to correspond to model date.
• Added a "restart-pointer file" to keep track of the latest restart file written. This way the user doesn't have to figure out the name of the last restart file written to restart a run.

Bug fixes (no significant change to the climate):

• Calendar no longer off by 1 day.
• Fixed vector temporary that was improperly used outside of loop in radiation code (routine radabs).
• Corrected pressure levels used in routine difcor.
• Corrected minor problem with top of atmosphere radiation calculation (routine radtpl).
• Corrected minor problem with water vapor paths used in trace gas overlap (routine trcabn).
• Fixed potential out of bounds memory reference in buoyancy calculation (routine bouyan)
• Workaround added to LSM to address Cray compiler bug. See the CCM3 web-site for more information on this at:
  http://www.cgd.ucar.edu:80/cms/ccm3/news/ccm3.2_fix.html.

Bug fix plus tuning modification to restore the documented climate

• Overestimate of subcloud consumption of CAPE by moist convection. (routine closure). This error had the effect of suppressing moist convection, particularly shallow convection. The parameter adjustment required to restore the simulated climate changes the minimum CAPE for initiating convection from zero to 70 J/Kg (routine conv_ccm).

The CCM3 news page contains the code-patches for CCM3.2 for all the bug-fixes. The code patches by nature show the code changes in CCM3.6 that fix the above problems.
http://www.cgd.ucar.edu:80/cms/ccm3/news/bug_fixes_in_ccm3.6.html.