## Vertical boundary conditions

Discussion of how to use ROMS on different regional and basin scale applications.

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nmichelet
Posts: 31
Joined: Fri Oct 02, 2015 2:24 pm
Location: Cerema

### Vertical boundary conditions

Hello everyone,
I am currently trying to find where is the vertical boundary condition in the model, in order to modify the condition on u.
Can you help me to find where the next equation is in the model
Km(du/dz) = tau_x^b

# if defined UV_LOGDRAG
!
! Set logarithmic bottom stress.
!
DO j=JstrV-1,Jend
DO i=IstrU-1,Iend
cff1=1.0_r8/LOG((z_r(i,j,1)-z_w(i,j,0))/ZoBot(i,j))
cff2=vonKar*vonKar*cff1*cff1
wrk(i,j)=MIN(Cdb_max,MAX(Cdb_min,cff2))
END DO
END DO
DO j=Jstr,Jend
DO i=IstrU,Iend
cff1=0.25_r8*(v(i ,j ,1,nrhs)+ &
& v(i ,j+1,1,nrhs)+ &
& v(i-1,j ,1,nrhs)+ &
& v(i-1,j+1,1,nrhs))
cff2=SQRT(u(i,j,1,nrhs)*u(i,j,1,nrhs)+cff1*cff1)
bustr(i,j)=0.5_r8*(wrk(i-1,j)+wrk(i,j))* &
& u(i,j,1,nrhs)*cff2
# ifdef LIMIT_BSTRESS
cff3=cff*0.5_r8*(Hz(i-1,j,1)+Hz(i,j,1))
bustr(i,j)=SIGN(1.0_r8, bustr(i,j))* &
& MIN(ABS(bustr(i,j)), &
& ABS(u(i,j,1,nrhs))*cff3)
# endif

I found this which calculate the bottom shear stress "bustr", but I don't know where the boundary condition is defined.
Thanks

kate
Posts: 3808
Joined: Wed Jul 02, 2003 5:29 pm
Location: CFOS/UAF, USA

### Re: Vertical boundary conditions

A search on bustr shows that it is used in lmd_bkpp, lmd_skpp, pre_step3d and in rhs3d. In rhs3d, it is being added to rufrc, the barotropic expression of the baroclinic terms as used in the depth-integrated equations. In pre_step3d, it is being used as the bottom boundary condition to the vertical diffusion term in a tri-diagonal solve.

nmichelet
Posts: 31
Joined: Fri Oct 02, 2015 2:24 pm
Location: Cerema

### Re: Vertical boundary conditions

Thank you for your help Kate it is very useful