FJORD TIDAL CASE

Fjord Tidal Test Case

This WikiROMS article is currently under HEAVY construction. This message will be erased when active construction is finished (in 1 or 2 days). April 21, 2008

There are a few ways to setup tidal forcing in ROMS (...learn more about tides in ROMS). This tutorial will explain the simplest way, which is to prescribe (analytically) tidal variations in sea-surface height at a open boundary (this uses a FLATHER/CHAPMAN combination). I learned this trick from hetland in this forum post (at the bottom).

RESTRICTIONS: This technique is ONLY applicable in cases with one relatively narrow open boundary (say < 10 km). In this cases, the tidal height along the open boundary is essentially uniform and can be prescribed analytically.

PREREQUISITES: This tutorial assumes that you have (1) downloaded ROMS, (2) installed it in your computer (or cluster), and (3) tested it by compiling and running one of the included test cases. If you haven't done all the above, check the "Getting Started" and "Tutorials" WikiROMS sections.

Geographical Preamble

This application is for Ship Harbour, an estuarine fjord in Nova Scotia, Canada. Click here to see the location in Google. Tides are semidiurnal and tidal range is 1.4 m on average and 2 m on spring tides. Ship Harbour is a long embayment (~7 km) with an open (EAST) boundary of ~1 km, therefore it is an ideal candidate for the type of analytical tidal forcing taught in this tutorial. For now I will only include tidal forcing, however, there is a river at the uppermost end of the estuary, which discharges freshwater at an annual average rate of 18 m³ s^-1. I plan to write another tutorial on how to add a river, but for now is only tides.

Grid Generation

The first step to set up a realistic application is to set up a realistic grid. There are several software packages to generate ROMS grids; SEAGRID and GRIDGEN being the most popular ones. I used the much-less-fancy EASYGRID, which is a bit easier to get up and running.

DOWNLOAD HERE to get the GRID and INITIALIZATION files required for this tutorial. Alternatively, you can create your own grid and initialization files for this tutorial using the grid-generation software of your choice. You can download the bathymetry and coastline data for Ship Harbour Fjord HERE.

NOTE: I also wrote a tutorial for grid generation using EASYGRID. The output of that tutorial are the grid and initialization files used in this tutorial (see above). So if you want to start from scratch, you should begin with the EASYGRID tutorial.

Compiling ROMS with tides

Before we compile ROMS, we need to create a header (.h) file with the appropriate cpp definitions that turn ON the analytical tides. Also, we need to modify some analytical Fortran files, where we are going to specify how create the analytical tide.

Creating header (.h) file

Create a file named fjord.h and copy-paste the cpp definitions below:

/*
**
** Options for Tidal Fjord.
**
** Application flag:   FJORD
** Input script:       ocean_fjord.in
*/
#define UV_ADV                 /* use to turn ON or OFF advection terms  */
#define UV_COR                 /* use to turn ON or OFF Coriolis term    */
#define UV_QDRAG               /* use to turn ON or OFF quadratic bottom friction */
#define UV_VIS4                /* use to turn ON or OFF harmonic horizontal mixing */
#define MIX_S_UV               /* momentum mixing on s-surfaces */
#define DJ_GRADPS              /* use if splines density Jacobian (Shchepetkin, 2000) */
#define TS_U3HADVECTION        /* use if 3rd-order upstream horiz. advection */
#define TS_C4VADVECTION        /* use if 4th-order centered vertical advection */
#define SOLVE3D                /* use if solving 3D primitive equations */
#define SPLINES                /* use to activate parabolic splines reconstruction */
/* */
#define ANA_SMFLUX             /* use if analytical surface momentum stress */
#define ANA_STFLUX             /* use if analytical surface temperature flux */
#define ANA_SSFLUX             /* use if analytical surface salinity flux */
#define ANA_BSFLUX             /* use if analytical bottom salinity flux */
#define ANA_BTFLUX             /* use if analytical bottom temperature flux */
#define MASKING                /* use if analytical masking is enabled */
#define EAST_FSCHAPMAN         /* use if free-surface Chapman condition*/
#define EAST_M2FLATHER         /* use if 2D momentum Flather condition*/
#define EAST_M3RADIATION       /* use if 3D momentum radiation condition*/
#define EAST_TRADIATION        /* use if tracers radiation condition*/
#define ANA_FSOBC              /* use if analytical free-surface boundary conditions*/
#define ANA_M2OBC              /* use if analytical 2D momentum boundary conditions*/

The last 6 cpp definitions are the responsible for the analytical tidal forcing.
If your open boundary is not EAST... change EAST_FSCHAPMAN, EAST_M2FLATHER, EAST_M3RADIATION and EAST_TRADIATION to represent your open boundary (e.g. WEST__FSCHAPMAN for a west open boundary... etc.).

Modify ana_fsobc.h

You will have to edit the file ana_fsobc.h (located in trunk/ROMS/Functionals) to tell ROMS to estimate surface height analytically when running the FJORD case. Below is a snippet of the end of the file... you have to ADD the green code.

#elif defined TEST_CHAN
     IF (WESTERN_EDGE) THEN
       cff=0.0_r8
       DO j=JstrR,JendR
         BOUNDARY(ng)%zeta_west(j)=cff
       END DO
     END IF
     IF (EASTERN_EDGE) THEN
       cff=-0.4040_r8*MIN(time(ng)/150000.0_r8,1.0_r8)
       DO j=JstrR,JendR
         BOUNDARY(ng)%zeta_east(j)=cff
       END DO
     END IF
#elif defined WEDDELL
     IF (WESTERN_EDGE) THEN
       fac=TANH((tdays(ng)-dstart)/1.0_r8)
       omega=2.0_r8*pi*time(ng)/(12.42_r8*3600.0_r8)  !  M2 Tide period
       val=0.53_r8+(0.53_r8-0.48_r8)/REAL(Iend+1,r8)
       phase=(277.0_r8+(277.0_r8-240.0_r8)/REAL(Iend+1,r8))*deg2rad
       DO j=JstrR,JendR
         BOUNDARY(ng)%zeta_west(j)=fac*val*COS(omega-phase)
       END DO
     END IF
     IF (EASTERN_EDGE) THEN
       fac=TANH((tdays(ng)-dstart)/1.0_r8)
       omega=2.0_r8*pi*time(ng)/(12.42_r8*3600.0_r8)  !  M2 Tide period
       val=0.53_r8+(0.53_r8-0.48_r8)
       phase=(277.0_r8+(277.0_r8-240.0_r8))*deg2rad
       DO j=JstrR,JendR
         BOUNDARY(ng)%zeta_east(j)=fac*val*COS(omega-phase)
       END DO
     END IF
#elif defined FJORD
     IF (WESTERN_EDGE) THEN
       fac=TANH((tdays(ng)-dstart)/1.0_r8)
       omega=2.0_r8*pi*time(ng)/(12.42_r8*3600.0_r8)  !  M2 Tide period
       val=0.53_r8+(0.53_r8-0.48_r8)/REAL(Iend+1,r8)
       phase=(277.0_r8+(277.0_r8-240.0_r8)/REAL(Iend+1,r8))*deg2rad
       DO j=JstrR,JendR
         BOUNDARY(ng)%zeta_west(j)=fac*val*COS(omega-phase)
       END DO
     END IF
     IF (EASTERN_EDGE) THEN
       fac=TANH((tdays(ng)-dstart)/1.0_r8)
       omega=2.0_r8*pi*time(ng)/(12.42_r8*3600.0_r8)  !  M2 Tide period
       val=0.53_r8+(0.53_r8-0.48_r8)
       phase=(277.0_r8+(277.0_r8-240.0_r8))*deg2rad
       DO j=JstrR,JendR
         BOUNDARY(ng)%zeta_east(j)=fac*val*COS(omega-phase)
       END DO
     END IF      
#else
     IF (EASTERN_EDGE) THEN
       DO j=JstrR,JendR
         BOUNDARY(ng)%zeta_east(j)=0.0_r8
       END DO
     END IF
     IF (WESTERN_EDGE) THEN
       DO j=JstrR,JendR
         BOUNDARY(ng)%zeta_west(j)=0.0_r8
       END DO
     END IF
     IF (SOUTHERN_EDGE) THEN
       DO i=IstrR,IendR
         BOUNDARY(ng)%zeta_south(i)=0.0_r8
       END DO
     END IF
     IF (NORTHERN_EDGE) THEN
       DO i=IstrR,IendR
         BOUNDARY(ng)%zeta_north(i)=0.0_r8
       END DO
     END IF
#endif
     RETURN
     END SUBROUTINE ana_fsobc_tile

Modify ana_m2obc.h

You will have to edit the file ana_m2obc.h (located in trunk/ROMS/Functionals) to tell ROMS to estimate currents analytically when running the FJORD case. Below is a snippet of the end of the file... you have to ADD the green code.

#elif defined WEDDELL
     IF (WESTERN_EDGE) THEN
       fac=TANH((tdays(ng)-dstart)/1.0_r8)
       omega=2.0_r8*pi*time(ng)/(12.42_r8*3600.0_r8)  !  M2 Tide period
       minor=0.0143_r8+(0.0143_r8+0.010_r8)/REAL(Iend+1,r8)
       major=0.1144_r8+(0.1144_r8-0.013_r8)/REAL(Iend+1,r8)
       phase=(318.0_r8+(318.0_r8-355.0_r8)/REAL(Iend+1,r8))*deg2rad
       angle=(125.0_r8+(125.0_r8- 25.0_r8)/REAL(Iend+1,r8))*deg2rad
       DO j=JstrR,JendR
         val=0.5_r8*(angler(Istr-1,j)+angler(Istr,j))
         BOUNDARY(ng)%ubar_west(j)=fac*(major*COS(angle-val)*          &
    &                                         COS(omega-phase)-        &
    &                                   minor*SIN(angle-val)*          &
    &                                         SIN(omega-phase))
       END DO
       DO j=Jstr,JendR
         val=0.5_r8*(angler(Istr-1,j-1)+angler(Istr-1,j))
         BOUNDARY(ng)%vbar_west(j)=fac*(major*SIN(angle-val)*          &
    &                                         COS(omega-phase)-        &
    &                                   minor*SIN(angle-val)*          &
    &                                         COS(omega-phase))
       END DO
     END IF
     IF (EASTERN_EDGE) THEN
       fac=TANH((tdays(ng)-dstart)/1.0_r8)
       omega=2.0_r8*pi*time(ng)/(12.42_r8*3600.0_r8)  !  M2 Tide period
       minor=0.0143_r8+(0.0143_r8+0.010_r8)
       major=0.1144_r8+(0.1144_r8-0.013_r8)
       phase=(318.0_r8+(318.0_r8-355.0_r8))*deg2rad
       angle=(125.0_r8+(125.0_r8- 25.0_r8))*deg2rad
       DO j=JstrR,JendR
         val=0.5_r8*(angler(Iend,j)+angler(Iend+1,j))
         BOUNDARY(ng)%ubar_east(j)=fac*(major*COS(angle-val)*          &
    &                                         COS(omega-phase)-        &
    &                                   minor*SIN(angle-val)*          &
    &                                         SIN(omega-phase))
       END DO
       DO j=Jstr,JendR
         val=0.5_r8*(angler(Iend+1,j-1)+angler(Iend+1,j))
         BOUNDARY(ng)%vbar_east(j)=fac*(major*SIN(angle-val)*          &
    &                                         COS(omega-phase)-        &
    &                                   minor*SIN(angle-val)*          &
    &                                         COS(omega-phase))
       END DO
     END IF
#elif defined FJORD
     IF (WESTERN_EDGE) THEN
       fac=TANH((tdays(ng)-dstart)/1.0_r8)
       omega=2.0_r8*pi*time(ng)/(12.42_r8*3600.0_r8)  !  M2 Tide period
       minor=0.0143_r8+(0.0143_r8+0.010_r8)/REAL(Iend+1,r8)
       major=0.1144_r8+(0.1144_r8-0.013_r8)/REAL(Iend+1,r8)
       phase=(318.0_r8+(318.0_r8-355.0_r8)/REAL(Iend+1,r8))*deg2rad
       angle=(125.0_r8+(125.0_r8- 25.0_r8)/REAL(Iend+1,r8))*deg2rad
       DO j=JstrR,JendR
         val=0.5_r8*(angler(Istr-1,j)+angler(Istr,j))
         BOUNDARY(ng)%ubar_west(j)=fac*(major*COS(angle-val)*          &
    &                                         COS(omega-phase)-        &
    &                                   minor*SIN(angle-val)*          &
    &                                         SIN(omega-phase))
       END DO
       DO j=Jstr,JendR
         val=0.5_r8*(angler(Istr-1,j-1)+angler(Istr-1,j))
         BOUNDARY(ng)%vbar_west(j)=fac*(major*SIN(angle-val)*          &
    &                                         COS(omega-phase)-        &
    &                                   minor*SIN(angle-val)*          &
    &                                         COS(omega-phase))
       END DO
     END IF
     IF (EASTERN_EDGE) THEN
       fac=TANH((tdays(ng)-dstart)/1.0_r8)
       omega=2.0_r8*pi*time(ng)/(12.42_r8*3600.0_r8)  !  M2 Tide period
       minor=0.0143_r8+(0.0143_r8+0.010_r8)
       major=0.1144_r8+(0.1144_r8-0.013_r8)
       phase=(318.0_r8+(318.0_r8-355.0_r8))*deg2rad
       angle=(125.0_r8+(125.0_r8- 25.0_r8))*deg2rad
       DO j=JstrR,JendR
         val=0.5_r8*(angler(Iend,j)+angler(Iend+1,j))
         BOUNDARY(ng)%ubar_east(j)=fac*(major*COS(angle-val)*          &
    &                                         COS(omega-phase)-        &
    &                                   minor*SIN(angle-val)*          &
    &                                         SIN(omega-phase))
       END DO
       DO j=Jstr,JendR
         val=0.5_r8*(angler(Iend+1,j-1)+angler(Iend+1,j))
         BOUNDARY(ng)%vbar_east(j)=fac*(major*SIN(angle-val)*          &
    &                                         COS(omega-phase)-        &
    &                                   minor*SIN(angle-val)*          &
    &                                         COS(omega-phase))
       END DO
     END IF      
#else
     IF (EASTERN_EDGE) THEN
       DO j=JstrR,JendR
         BOUNDARY(ng)%ubar_east(j)=0.0_r8
       END DO
       DO j=Jstr,JendR
         BOUNDARY(ng)%vbar_east(j)=0.0_r8
       END DO
     END IF
     IF (WESTERN_EDGE) THEN
       DO j=JstrR,JendR
         BOUNDARY(ng)%ubar_west(j)=0.0_r8
       END DO
       DO j=Jstr,JendR
         BOUNDARY(ng)%vbar_west(j)=0.0_r8
       END DO
     END IF
     IF (SOUTHERN_EDGE) THEN
       DO i=Istr,IendR
         BOUNDARY(ng)%ubar_south(i)=0.0_r8
       END DO
       DO i=IstrR,IendR
         BOUNDARY(ng)%vbar_south(i)=0.0_r8
       END DO
     END IF
     IF (NORTHERN_EDGE) THEN
       DO i=Istr,IendR
         BOUNDARY(ng)%ubar_north(i)=0.0_r8
       END DO
       DO i=IstrR,IendR
         BOUNDARY(ng)%vbar_north(i)=0.0_r8
       END DO
     END IF
#endif
     RETURN
     END SUBROUTINE ana_m2obc_tile

Tidal Forcing

Dummy text... No real information here yet