Ask about Z0m（roughness lengths for momentum）in CLM50_Tech_Note

[majun]

Dear scientist,
Recently, I read the chapter5 "Momentum, Sensible Heat, and Latent Heat Fluxes" in CLM50_Tech_Note, however, a question bothered me .
I want to know the Influence factors of Z0m（roughness lengths for momentum）, I just found plant height and adjusted for canopy density that influenced the calculation of Z0m in the formula of (5.125). However, I found LAI and atmospheric wind speed also influenced Z0m in other papers(not the CLM50_Tech_Note), so I want to what's the Influence factors of Z0m in CLM5.0,
Thank you very much!!

 

[oleson]

Canopy density is represented by LAI (and SAI - stem area index) in equation 5.127.
Wind speed doesn't directly effect z0m.

 

[majun]

thanks a lot！

 

[majun]

Canopy density is represented by LAI (and SAI - stem area index) in equation 5.127.
Wind speed doesn't directly effect z0m.

furthermore, I want to ask that how to calculate LAI in CLM5.0? just using look-up table? what's more, z0m is a constant or is changing with surface change?

 

[oleson]

For LAI, please see section 2.2.1.3 of the technical note:

2.2. Surface Characterization, Vertical Discretization, and Model Input Requirements — ctsm release-clm5.0 documentation

I'm not sure what you mean by "surface change"?

 

[majun]

For LAI, please see section 2.2.1.3 of the technical note:

2.2. Surface Characterization, Vertical Discretization, and Model Input Requirements — ctsm release-clm5.0 documentation

I'm not sure what you mean by "surface change"?

thanks a lot. I mean that is z0m a constant that is invariant in space and time? is it just affected by PFT-specific types? I see that canpoy top and bottom heights do, but LAI and SAI are calculated dynamically

 

[oleson]

z0m is not a constant that is invariant in space and time.
The equation for z0m (5.125) means that it varies by LAI, SAI, and canopy top height. LAI, SAI, and canopy top height vary by pft. When the BGC model is active, LAI, SAI, and canopy top height are prognostic and therefore vary in time.

 

[majun]

z0m is not a constant that is invariant in space and time. The equation for z0m (5.125) means that it varies by LAI, SAI, and canopy top height. LAI, SAI, and canopy top height vary by pft. When the BGC model is active, LAI, SAI, and canopy top height are prognostic and therefore vary in time.

thanks very much!