[MITgcm-support] internal tide beam in nonuniform stratification

[Sherry]

Hi everyone,

I am a grad student trying to model internal tide beams as they propagate
up towards the surface after being generated in the open ocean.

I started with the internal wave example in verifications and modified
obcs_calc.F to make an upward beam that's the sum of 10 modes.
I've been encountering a barotropic instability that starts in w, which is
sometimes worsened by decreasing Uinflow or deltaT, or increasing the
number of points per process. (Decreasing the forcing frequency also led to
increased instability, and switching to rigid lid improved this.)

Right now I have a (seemingly) stable configuration for H=4200m (dz=20m)
and Lx=120km (dx=120m), with uniform stratification, that ran for more than
22 wave periods (M2 period = 12.42 hrs). I am interested in the effect of
different stratification profiles, and would like to start with a simple
Gaussian shape where the maximum bvsq is ~1e-4. The attached gendata.py (it
is written in python) makes a temperature profile that has max bvsq ~2e-5.
When I increase max bvsq slightly to ~3e-5 (by increasing the drho_rel
parameter to 0.2*3.6e-3), w-velocity becomes unstable after 1 wave period.

Any kind of help for this specific configuration, or for learning how to
deal with the model blowing up in general, would be much appreciated.

Thank you,

Sherry Chou
schou at hawaii.edu

Department of Oceanography
UH Manoa, Hawaii

[image: Inline image 1]
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