[MITgcm-support] Polar filter, Channel and momentum forcing

[Yuan Lian]

Hi,

I am using the atmospheric model of MITgcm code. I have some problems with
polar filter,  doing a channel(for example: from -45-45 degree) and
adding a momentum forcing.

First, I can't find find filter specially for poles if doing a global
simulation. Two filters are presented in MITgcm packages-Shapiro filter
and Zonal filter. To my understanding, Shapiro filter is applied globally
and FFT filter will only take care of the zonal but not polar issues.

Second, it's hard to make a channel working, say from -45-45degrees. The
problem is that instability happens at south bounfary and north boundary,
I guess the filter doesn't do a good job at boundaries. Is there any
successful test done for channel with atmospheric model? Or is it helpful
to define zonal_filt_lat being greater than 45 degree if I do a channel
from -45-45 degrees?

Third, does momentum forcing work for atmospheric model? I modified
external_forcing.F, where I put a momentum forcing for du/dt=-(u-u0)/T,
here T is a time scale. I am trying to relax the zonal wind to a given
profile u0, I didn't give any forcing to v,w and temperature. However the
wind will never relax to the profile I expected. I am sure the code works
for a temperature forcing since HS94' model can run well. But why it
doesn't work for momentum forcing?

Any suggestions for my problems? I think it will be great if an
experimental model is included in MITgcm verification according to the
problems above.

Greatly appreciate for your help.

Yuan