how to output the vertical velocity "wt" in MOM6

[ma1983]

Dear ALL,

I am a new with MOM6. I want to online output the vertical velocity "wt" as MOM4/MOM5 does. How can I do it?

Thank you very much for help in advance.

Best,
Libin Ma

 

[kshedstrom@alaska_edu]

This is an ongoing topic of discussion - how to compute such a beast. The model in ALE mode make computing it very tricky.

 

[clpwolfe]

If you're using z* coordinates and you just want a diagnostic that gives you a sense of the vertical velocity, you can calculate the velocity that balances the divergence of the transports uh and vh by integrating the divergence vertically (from the bottom assuming w = 0 there, or from the top with an estimate of the vertical velocity from the evolution of SSH). This best done with time-mean outputs, since it is otherwise difficult to determine exactly which time level the vertical velocity should instantaneously live. Further, the z* coordinates themselves move as the free surface moves up and down, but this should be a small effect if you take a long enough time mean.

What you get out of this isn't going to be the same as the velocity used to "advect" tracers and momentum, but the model never really uses such a velocity since vertical motion is handed by coordiante motion followed by remapping.