Lateral Boundary Conditions


WRF Dynamics Contents

Dynamics Overview
Hybrid Vertical Coordinate
Diffusion
Damping
Advection
Other Dynamics Options
Lateral Boundary Conditions


Lateral Boundary Conditions for Idealized Cases

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.


Lateral Boundary Conditions for Real-data Cases

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.