Coupling To WW3

Coupling with WaveWatch III is currently a work in progress. We have established two-way coupling between ERF and WaveWatch III (WW3), in which WW3 sends ERF \(Hwave\) (significant wave height) and \(Lwave\) (mean wavelength) at the lower boundary, and ERF sends WW3 the wind magnitude and direction:

\[U_{wind} = \sqrt{u^{2} + v^2}\]

\[\theta = \mathrm{arctan}{\frac{v}{u}}\]

The bidirectional send and receive currently implemented within the WaveWatch III (WW3) regression test ww3_ts3. This regression test uses the wind velocity \(U_{wind}\) and wind direction \(\theta\) sent from ERF to compute an atmospheric source term \(S_in\) in the ST6 subroutine in WW3. The values for \(Hwave\) and \(Lwave\) are then sent to ERF to compute the surface roughness parameter \(z_0\) through a fixed point iteration:

\[z_{0} = 1200.0 Hwave (\frac{Hwave}{Lwave})^{4.5} + \frac{0.11 \mu}{u_*}\]

To run the coupled model:

git clone --recursive git@github.com:erf-model/ERF
cd ERF/Exec/CanonicalTests/ABL/WW3_coupling
make -j4 USE_WW3_COUPLING=TRUE
cd ../../../../Submodules/WW3
./model/bin/w3_setup model -c gnu -s Ifremer1
cd regtests
./bin/run_cmake_test -C MPMD -n 2 -p mpirun -f -s ST6_PR1_MPI -w work ../model ww3_ts3

Modifications to the problem size and geometry, as well as other parameters can be done in the inputs_mpmd file. The plt files as well as relevant outputs can be viewed in the regtests/ww3_ts3/work directory.