Tidal forcing on 3D momentum boundary field

[chysun]

Hi,
I try to figure out how tides is put into ROMS boundary.

Following what wikiroms says there are three ways to include tides:
1.You can specify a time-dependent boundary condition file that temporally resolves the tides and skip the tides file entirely.
2.You can specify SSH_TIDES and/or UV_TIDES and provide a tides file and skip the boundary condition file entirely
3.You can specify other 2d currents and surface elevation signals as coming in, plus have tides and use the ADD_M2OBC and ADD_FSOBC options.

When I read the set_tides.F it tells me that tidal currents are added into barotropic u/v momentum at boundaries only while no tidal constituent is applied to 3d u/v momentum boundaries.

Code: Select all

#  ifdef ADD_M2OBC
              BOUNDARY(ng)%ubar_west(j)=BOUNDARY(ng)%ubar_west(j)+      &
     &                                  Utide(Istr,j)
#  else
              BOUNDARY(ng)%ubar_west(j)=Utide(Istr,j)
#  endif

Here are my doubts,
1)Does it make sense to have a non-tide 3d u/v momentum boundary conditions if that's what I see?
2)I've also wondering how ROMS make barotropic momentum that includes tides in the depth-integrated momentum equation consistent with 3d momentum that does not include tides,especially when I have a Nudging boundary condition of 3d momentum?

Some posts about tides issues such as,
viewtopic.php?f=2&t=61&hilit=tangential,
viewtopic.php?f=14&t=1911&p=6923&hilit= ... ecc9#p6923,
are illuminating but few of them mentioned about 3d tidal forcing.

It is appreciated to give some comments about tidal forcing at 3d field!


Thanks in advance,
Haiyun

[kate]

The model computes 2d flow and 3d flow independently and has to make them consistent at the end of each baroclinic timestep. To do that, the model throws out the 3d estimate of barotropic transport and replaces it with the transport from the 2d solution. That's how tides get into the 3d flow without you having to specify it on the boundary - as long as the tides are part of the 2d solution.

[chysun]

Dear Kate,
Thanks for your reply.
I got the answer from ROMS codes about time stepping 2d&3d momentum equations(step2d_LE_AM3.F step3d_uv.F) as you noticed.