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The NCAR Community Climate Model (CCM3)CCM Users;
We have come up with a fix for the "68 year" problem originally brought up by user on the ccm-users list. The problem he encountered (on a SUN) was that 32-bit integer computations would overflow at approximately year 68 of the simulation in the routine which computes calendar day information. The fix involves a few lines of changes to the routine calendr.F in CCM3.6 (and CCM3.6.6). A few of the computations are now forced to be done using 64-bit integer arithmetic. We have tested the fix on all platforms on which the CCM is supported and gotten bit-for-bit answers as compared to the old code (for a one-day run). An offline driver test was run out to 7000 years of simulation and no problems were found.
The fix we are providing applies to CCM3.6 and CCM3.6.6. For those who wish to retrofit the changes into CCM3.2, you will need to change caldyi.F in addition to calendr.F.
Please let us know if you encounter further problems.
CCM Core Group