[Wrf-users] what is difference between Z0 and ZNT

[Feng Liu]

Hi, WRF-uers,
I am wondering what are the difference between "Z0, Background Roughness
Length" and "ZNT, Time Varying Roughness Length" in physics. I checked
the both from my model runs, and has a twofold fact, First, ZNT is
generally greater than  Z0 at the same location, especially in urban
area. Second, ZNT does not change with time, why defined as
"Time-Varying Roughness Length".  Which roughness length should be used
for calculating surface wind speed via Monin-Obhukov similarity theory?
Thanks.
Feng