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Lateral Boundary Conditions
===========================

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WRF Dynamics Contents
---------------------

`Dynamics Overview`_ |br|
`Hybrid Vertical Coordinate`_ |br|
Diffusion_ |br|
Damping_ |br|
Advection_ |br|
`Other Dynamics Options`_ |br|
`Lateral Boundary Conditions`_

.. _`Dynamics Overview`: dynamics.html
.. _`Hybrid Vertical Coordinate`: hybrid_vert_coord.html
.. _Diffusion: diffusion.html
.. _Damping: damping.html
.. _Advection: advection.html
.. _`Other Dynamics Options`: other_dynamics.html
.. _`Lateral Boundary Conditions`: lat_bdy_conditions.html 

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Lateral Boundary Conditions for Idealized Cases
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For each idealized case (found in test/em_<case>), a default namelist.input file is provided and there are varying lateral boundary conditions default settings for the different cases. These settings are found in the "&bdy_control" section, and should be set for each domain. *The following options are only available for idealized cases*.

    * **periodic_x** and **periodic_y** : set to ".true." for periodic boundary conditions in the x and y directions. This means that (for e.g., the conditions/values that leave out of x_end of the domain are returned to the x_start position, as if the two sides are connected.

    * **open_xs, open_xe, open_ys,** and **open_ye** : set to ".true." for open boundary conditions along the x-start, x-end, y-start, and/or y-end boundaries. This means conditions/values come in from one direction and leave without being cycled back in.

    * **symmetric_xs, symmetric_xe, symmetric_ys,** and **symmetric_ye** : set to ".true." for symmetric boundary conditions along the x-start, x-end, y-start, and/or y-end boundaries. This means all variables have the same value and gradients at the same distance from the boundary.

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Lateral Boundary Conditions for Real-data Cases
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The real-data case (found in test/em_real) a namelist.input file is provided with default lateral boundary condition settings. These are found in the "&bdy_control" section, and should be set for each domain. *The following options are only available for real-data cases*.


    * **specified** : The first row and column are specified with external model values (spec_zone=1, which should not be modified). The rows and columns in "relax_zone" have values blended from an external model and WRF. This can be used with periodic_x in tropical channel simulations. The "specified=.true." option can only be used for domain 1.

    * **spec_exp** \: Exponential multiplier for the relaxation zone ramp, used with a specified boundary condition. 
        * spec_exp=0. : linear ramp (default)
        * spec_exp=0.33 : ~3*dx exp decay factor (this may be useful for long simulations)

    * **spec_bdy_width** : total number of rows for specified value nudging. The default value is 5. 

    * **spec_zone** : number of points in the specified zone when "specified=.true." The default value is 1 and should not be changed!

    * **relax_zone** : number of points in the relaxed zone when specified=.true. The default value is set to 4. This value may be changed, as long as spec_bdy_width=spec_zone + relax_zone. 

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