.. _ocean_drying_slope:

drying_slope
=============

The ``ocean/drying_slope`` test group reproducs the tidal channel flow test case
from `Warner et al. (2013) <http://dx.doi.org/10.1016/j.cageo.2013.05.004>`_
which was originally presented in
`Oey (2005) <https://doi.org/10.1016/j.ocemod.2004.06.002>`_.

The domain is 2-d with a channel sloping in the x-dimension and periodic in the
y-dimension. The channel length is set to 25 km and slopes with an aspect ratio
of 0.1. The channel width is 6km for all simulations. The channel is initialized
as dry with a minimum layer thickness. The water level at the seaward end is
oscillated sinusoidally with a period of 0.5 days as

.. math::
   \zeta_{east} = 10.0 \sin(\pi/0.5t) - 10.0

.. image:: images/drying_slope_forcing.png
   :width: 500 px
   :align: center

Temperature and salinity are constant throughout the domain with values of 20
degC and 35 PSU, respectively. Two different linear drag bottom roughness
factors of 0.0025 and 0.01 are applied in separate simulations.

By default, there are 10 vertical layers. The sigma vertical coordinate is
used. Horizontal resolution of 250m and 1 km are available.

The test group includes 1 test case.  The test case has 4 steps. The
``initial_state`` defines the mesh and initial conditions for the model. For
the ``sigma`` vertical coordiante, two ``forward`` steps are run, one for each
Rayleigh damping coefficient; for the ``single_layer`` case, one ``forward``
step is run at one value of the explicit bottom drag coefficient. The ``viz``
step performs visualization of the ssh field. For the ``sigma`` case, the
``viz`` step also produces a comparison plot with the analytical solution as
well as the solution from the ROMS model.

.. image:: images/drying_slope_validation.png
   :width: 500 px
   :align: center


config options
--------------

The config options for this test case are:

.. code-block:: cfg

   # Options related to the vertical grid
   [vertical_grid]
   
   # Number of vertical levels
   vert_levels = 10
   
   # The type of vertical coordinate (e.g. z-level, z-star)
   coord_type = sigma
   
   # config options for drying slope test cases
   [drying_slope]
   
   # the number of grid cells in x and y
   nx = 6
   
   # config options for visualizing drying slope ouptut
   [drying_slope_viz]
   
   # whether to generate movie
   generate_movie = False

   # frames per second for movies
   frames_per_second = 30
   
   # movie format
   movie_format = mp4

All units are mks.

default
-------

``ocean/drying_slope/1km/default`` is the default version of the drying slope
test case for two short (12h) test runs with two different drag coefficients
and validation of sea surface height through visual inspection against analytic
and ROMS solutions.