Why does Z0 vary?


Why does Z0 vary?

Postby rmclare » Wed Apr 04, 2018 6:15 pm

Hi all,

It's my understanding that the variable Z0 is the background surface roughness and should not vary at all over time as opposed to ZNT. Unless I misunderstand, Z0 should always be identical for the same domain.

I've recently looked at the Z0 variable in two wrfout files from 6 days apart and there are a lot of places where the two do not match up and I'm wondering why this would happen to the background roughness. Does anyone know? Am I just wrong about what background surface roughness means?

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Re: Why does Z0 vary?

Postby BHajni » Tue May 29, 2018 2:24 am

Hi Ryan,

Z0 is not a property of the domain, but a property of a grid cell and it depends on the landuse, as the roughness depends on vegetation height and in less extent vegetation density i.e. LAI. If you have a lots of cropland surfaces and your setting is in spring/summer the z0 values should differ according to the VEGPARM.TBL values (especially if you use noah_mp with dynamic vegetation option).

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