[MITgcm-support] body force in apply_forcing.F

[Bertrand Louis Rene Delorme]

Hi everyone,

I am trying to set up a configuration with just a steady, deep, zonal jet in the water column balanced by the Coriolis force. To do that, I prescribed the jet as initial condition (u0) and I added a body force (BF) in the v-momentum equation such that dv/dt = -f*u + BF with BF=f*u0. I used apply_forcing.F to incorporate the body force by adding the following lines in APPLY_FORCING_V:

DO j=1,sNy+1
       DO i=0,sNx+1
	yv = 0.5*(yC(i,j,bi,bj)+yC(i,j-1,bi,bj))
	gV_arr(i,j) = gV_arr(i,j) + 1E-7 * exp(-(rC(k)-mZ)**2/sigZ**2) * exp(-(yv-mY)**2/sigY**2)
       ENDDO
ENDDO

where (mY, mZ) are the coordinates of the center of the jet in the meridional plane, sigZ and sigY the e-folding scale in each direction, and yv is the y-coordinate on the V-grid. Concerning the initial condition for U, I was careful to define it on the U-grid. 

However, for some reasons, the jet is not perfectly balanced and low amplitude waves emanate from its center. I feel like I might be doing something inconsistent in apply_forcing.F, like not using the appropriate grid, but couldn't figure out what it is. If anyone has an idea on what might go wrong please let me know.

Thank you,

Bertrand