Model Coupling

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Model Coupling

The ROMS modeling system has been coupled to other fully developed models to provide increased modeling capabilites. For the coupling communications, we are using the Model Coupling Toolkit (http://www-unix.mcs.anl.gov/mct/). The original coupling is described in Warner, J.C., Perlin, N., and Skyllingstad, E.D. (2008). Using the Model Coupling Toolkit to couple earth system models, Environmental Modelling & Software, 23, 1240-1249. Since that publication, the coding has been modified to be more generic and allow interfaces to other couplers (such as ESMF).

The coupling provides a mechanism for data transfer between models while they are running concurrently (at the same time). The model coupling requires that each model still needs its own grid, input parameters file, its own time step, forcing files (information not acquired from the other model), and each model writes its own output in its own format (just as if it was not coupled) on its own time interval. However the models are compiled into one executable and exchange information at user defined synchronization intervals.

The current release of ROMS includes 2-way coupling to the wave model SWAN. For coupling to SWAN, the transferred fields are:

 Fields acquired from the WAVE Model:                                !
                                                                     !
    * Dwave      Wave direction.                                     !
    * Hwave      Wave height.                                        !
    * Lwave      Wave length.                                        !
    * Pwave_bot  Wave bottom period.                                 !
    * Pwave_top  Wave surface period.                                !
    * Wave_break Percent of breakig waves.                           !
    * Wave_dissip Wave energy dissipation.                           !
                                                                     !
 Fields sent to the WAVE Model:                                      !
                                                                     !
    * ubar       Depth integrated xi-direction velocity.             !
    * vbar       Depth integrated eta-direction velocity.            !
    * zeta       Water surface elevation.                            !
    * h          Bottom elevation.                                   !


For coupling to the Atmospheric Model WRF, (currently being tested, to be released in the future), the transferred fields are:

 Fields sent to the OCEAN Model:                                     !
                                                                     !
    * PSFC       Surface atmospheric pressure  (mb)                  !
    * RELH       Surface air relative humidity (-)                   !
    * T2         Surface 2m air temperature    (degC)                !
    * U10        U-Wind speed at 10 m          (m/s)                 !
    * V10        V-Wind speed at 10 m          (m/s)                 !
    * CLDFRA     Cloud fraction                (percent/100, so 0-1) !
    * RAIN       Precipitation                 (kg/m2/s)             !
    * SWDOWN     Short wave radiation          (Celsius m/s)         !
    * GLW        Long wave raditaion           (Celsius m/s)         !
    * USTRESS    Surface u-stress              (m2/s2)               !
    * VSTRESS    Surface v-stress              (m2/s2)               !
 Fields acquired from the OCEAN Model:                               !
                                                                     !
    * SST        Sea surface temperature       (degC)                !

The coupling must be compiled with MPI. Users need to first compile the Model Coupling Toolkit, as this library is linked to during the compilation. Examples of coupled applications distributed with the source code include the Tidal Inlet Test Case and the Tidal Headland Test case.

Users need to modify the coupling*.in file to ensure that the correct fields are being transferred. Users should also read the information for the swan.in file.