Cumulus: on or off for 5 km grid spacing?

[irratio]

Hello everyone,
I am interested in precipitation output from WRF. Currently I am defining my domains and I would like to ask if nested domains of 15km and 5km are a suitable choice for precipitation? Additionally, I am unsure if I need to activate the cumulus scheme for both domains, or only for the outer 15 km domain? I will be running various microphysics schemes and compare to observations to choose an option.
Thank you in advance.
Kind regards

 

[stanleyakor]

I turn off cumulus parameterization at 4km or smaller.

 

[kwerner]

Hello everyone,
I am interested in precipitation output from WRF. Currently I am defining my domains and I would like to ask if nested domains of 15km and 5km are a suitable choice for precipitation? Additionally, I am unsure if I need to activate the cumulus scheme for both domains, or only for the outer 15 km domain? I will be running various microphysics schemes and compare to observations to choose an option.
Thank you in advance.
Kind regards

Hi,
Apologies for the delay in response. Between 3-10 km is what we consider a "gray zone," where it's too coarse for reasonable cloud parameterization, but potentially too fine to keep cu_physics turned on. We typically recommend trying to stay away from domains with this grid-spacing, though 3km is used pretty often, and it's probably okay to set cu_physics = 0 for 3km domains.