[Mitgcm-support] Re: can you help me?

[mitgcm-support at dev.mitgcm.org]

It sounds like the decay is due to the backward implicit method used for the
external mode and is expected. The external waves are so fast that to stabilize
them we use implicit time-stepping and to avoid aliasing energy from unresolved
frequencies we use the backward method that damps motions. This is a common
technique in atmos/ocean models and amounts to filtering. I believe there
is an option to use Crank-Nicholson time-stepping but I'm not sure if it has
ever
been tested/used. The person who added the option is away so I'll forward msg to
him for later comment.

A.