Hi, Another reason that we utilize 64 bit precision is in developing algorithms. In particular, we rely heavily on diagnostics that detect whether tracer is conserved over a single time step. Numerous times one will code a new algorithm and make a mistake, and this mistake typically shows up clearly with the tracer time step diagnostics. The difference between precision of 1e-8 and 1e-16, or thereabouts, is the difference between a properly coded scheme and one that is not coded properly. Similar arguments hold for energetic consistency diagnostics derived from the momentum equation.
This argument for using full 64 bit precision is not an argument for always using such, since one could conceivably develop algorithms with 64 bit and turn it off for production runs. I believe the strongest arguments for 64 bits is what Pacanowski said in his email. We need to maintain negligible levels of spurious roundoff errors in the discretization of transport operators, especially where those operators act on a background meanstate with tight gradients (such as the oceanic pycnocline). Hope this helps to explain why we remain faithful to the 64 bit precision in mom4. I suspect similar arguments are used for other models as well. -Stephen -- Dr. Stephen M. Griffies phone: +1-609-452-6672 Geophysical Fluid Dynamics Laboratory FAX: +1-609-987-5063 P.O. Box 308, Forrestal Campus Site B email: [EMAIL PROTECTED] Princeton, NJ 08542 USA http://www.gfdl.noaa.gov/~smg ------------------------------------------------------- This SF.net email is sponsored by: VM Ware With VMware you can run multiple operating systems on a single machine. WITHOUT REBOOTING! Mix Linux / Windows / Novell virtual machines at the same time. Free trial click here: http://www.vmware.com/wl/offer/345/0 _______________________________________________ FMS-mom4 mailing list [EMAIL PROTECTED] https://lists.sourceforge.net/lists/listinfo/fms-mom4
