In WRF application, nested domain has always been used for weather/air quality modeling for the place of interest in a better resolution.

  The figure below is an example to illustrate that.

I have noticed that the ratio of grid resolution between outer(coarser) domain and inner(finer) domain are always be set in 3:1(In this case => 12:4).

Is there any reason in the aspects of physical process or computation?

  Is the ratio of 3:1 helpful for the interaction between the boundary?

I'm looking forward for your answers.

In WRF application, nested domain has always been used for weather/air quality modeling for the place of interest in a better resolution. The figure below illustrates this:

I have noticed that the ratio of grid resolution between outer  (coarser) domain and inner  (finer) domain are always set at 3:1 ratio.

Is there any reason in the aspects of physical process or computation? Is the ratio of 3:1 helpful for the interaction between the boundary?