16. Trouble-shooting

If you encounter problems getting LANL POP to run, a list of known bugs is maintained at the LANL POP website and the user should check there before contacting the developers. In addition, there are other common sources of error listed below with suggestions for avoiding such problems.

Users who have difficulty getting POP2 to run after reading the this manual and the CESM User’s Guide should send questions to cesm-help@cgd.ucar.edu

16.1. Timestep stability criteria

As part of the POP diagnostics, the Courant number for various processes can be output. The Courant number should always be less than one and often should be kept under 0.5 for stability. If such a CFL condition is exceeded, reducing the timestep may be a solution. However, it should be noted that often other underlying problems may be causing these limits to be exceeded (e.g. unrealistically high velocities) and reducing the timestep will only prolong the agony. In such cases, the particular CFL condition that is violated can help pinpoint the source of the problem.

16.2. Checking the global energy and work balances

16.3. Getting the right combination of mixing options

16.4. Getting the right combination of forcing options

16.5. Properly normalizing input salinity values

The units for salinity in the model are g/g. Care must be taken to renormalize salinity data, which is often in g/kg.