Momentum flux BC at the surface

[ajpeliz]

Hi,
I'm trying to develop a suite of ocean numerical Labs for students, and find Oceananigans to be the all in one perfect tool.
However I got stuck right at the beginning when I was developing a simple idealized surface ekman layer and an upwelling on a periodic channel case. I'm probably missing something very basic about the setup of a surface forcing through the FluxBoundaryConditions(\tau). No matter what I try, i can't see the expected anticyclonic rotation of the current vector relative to wind (ie, say \tau_x is zero and \tau_y positive) I expect u(0) and v(0) nearly the same and positive. Am i making a wrong interpretation of what \tau should be in FluxBoundaryConditions(\tau)?

Can you also tell how to setup the bottom stress? and what about lateral conditions? are we using free slip, no slip.

Thanks and sorry for such basic questions.

[glwagner]

No worries about the question! Right now, fluxes at the surface use a convention that a positive flux is upwards, into the atmosphere. Therefore a positive tau is removing momentum from the ocean, driving currents in the "negative" direction.

tl;dr --- try FluxBoundaryCondition(-tau).

[glwagner]

Can you also tell how to setup the bottom stress? and what about lateral conditions? are we using free slip, no slip.

All boundary conditions are specified in the same way via FieldBoundaryConditions. This example implements quadratic bottom drag:

https://clima.github.io/OceananigansDocumentation/stable/literated/tilted_bottom_boundary_layer/

and there is more information here

https://clima.github.io/OceananigansDocumentation/stable/model_setup/boundary_conditions/

Note, all fluxes are in the positive direction. The sign convention does not depend on the boundary under consideration (right now).