using gwd_opt=3 in 1km-resolution simulation

[Qianqian Huang]

Hi,
I'm running a simulation with 1km resolution, trying to use gwd_opt=3. I already know that gwd_opt=3 in 3km-resolution simulation could reduce the overestimation of near-surface wind speed at night. So now I'm trying to use it in 1km-resolution, although WRF user guide said that gwd_opt=3 is suitable to simulations with resolution greater than 1km.
The result is that there is almost no difference between gwd_opt=0 and 3 in simulating near-surface wind speed by 1km-resolution. Could you please explain the reason? Is the constraint in resolution this strict?

Look forward to the reply. Thanks!

Qianqian Huang

 

[weiwang]

In the scheme, the small scale drag turns off at exactly 1 km grid sizes. If you would like to test its effects, you may consider modify the parameter dxmin_ss (currently set to 1000 m) in WRF/phys/module_bl_gwdo_gsl.F.