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If the proportion of vegetation in the PFT is set in CLM5.0, and the bare land in the study area is set to 0, then the model will use Z0MV and Z0MV wh

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zqzq

zqzqzqzq
Member
Dear all,
When I output Z0MG, Z0HG, Z0MV, Z0HV, I found that Z0MG=Z0HG and Z0MV=Z0HV. Obviously this is not correct. For the underlying surface without vegetation cover, there is a corresponding mathematical formula between Z0MG and Z0HG. However, The output of CLM5 shows that the two are equal. What is the situation?In addition, when I set the corresponding vegetation coverage ratio in the PFT (as shown in the figure, crop etc. are set to 0), does the model use Z0MV and Z0HV to calculate the corresponding flux?
 

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oleson

Keith Oleson
CSEG and Liaisons
Staff member
As stated in the technical note and in the code, Z0MV=Z0HV=Z0QV.
The roughness length for scalars is less than that of momentum, which leads to a larger aerodynamic resistance to the atmosphere. This occurs because of the additional diffusion across the leaf boundary layer, and the additional resistance imparted by leaves (inferred from the smaller roughness length) is sometimes called the "excess resistance". Because we separately include the leaf boundary layer resistance (to the canopy air space), we use the momentum roughness length to calculate the aerodynamic resistance from the canopy air to the atmosphere.

Z0MG is different from Z0HG only for non-vegetated surfaces. For ground beneath vegetation, the momentum roughness length is used to calculate a turbulent transfer coefficient (see Eq. 2.5.122). The ground heat and water vapor roughness lengths are not used in this case.
 
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zqzq

zqzqzqzq
Member
Thank you very much for your reply.If I want to output long-wave radiation, short-wave radiation, and heat flux into soil, what are their corresponding abbreviations? For example, the abbreviation for dynamic roughness is Z0MV.
 
erik

erik

Erik Kluzek
CSEG and Liaisons
Staff member
Looks like this thread is resolved, but I'm moving it to the CLM specific forum.
 
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