Damping

WRF Dynamics Contents

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

There are several damping options available for WRF simulations. Each of these options can be set in the &dynamics section of namelist.input and are all independent of each other.

Upper Damping (damp_opt)

Upper damping options are added near the model top to control reflection from the upper boundary.

• damp_opt=1 : a layer of increased diffusion

• damp_opt=2 : a Rayleigh relaxation layer

• damp_opt=3 : an implicit gravity-wave damping layer

Vertical Velocity Damping (w_damping)

For operational robustness, vertical motion can be damped to prevent the model from becoming unstable with locally large vertical velocities. This only affects strong updraft cores, and has very little impact on results otherwise. Set w_damping=1 to turn it on. The default is =0 (off).

Divergence Damping (smdiv)

Setting smdiv controls horizontally-propagating sound waves. The default, and typical value is smdiv=0.1 (for each domain).

External Mode Damping (emdiv)

The emdiv option is an external mode filter coefficient for the mass coordinate model that controls upper-surface (external) waves. The default and typical value is emdiv=0.01 (for each domain) for real-data cases.

Time Off-centering (epssm)

This option controls vertically-propagating sound waves. Slightly forward-centering the vertical pressure gradient damps 3d divergence. This can be a useful option if the simulation is resulting in CFL errors near complex terrain. The default value is epssm=0.1 (for each domain), but can be set up to 0.5. Values higher than 0.5 can begin to provide inaccuracy.