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.

Could you help me please

Thanks

## Vertical boundary conditions

### 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.

### Re: Vertical boundary conditions

Thank you for your help Kate it is very useful