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surface drag

paulino

Paulino Ajiquichi
New Member
What version of the code are you using?

I am using CESM2.1.5

Have you made any changes to files in the source tree?
I have not made any change yet

Describe your problem or question:

Dear CESM staff:

I am working with the following component set: 2000_CAM60_CLM50%BGCDV-CROP_CICE%PRES_DOCN%DOM_MOSART_CISM2%NOEVOLVE_SWAV
I want am trying to simulate the effect of large scale of wind farms ( which increase surface friction) in North Africa. My idea is to parameterize the wind farms increasing the surface drag (or drag coefficient). So, I am looking for recommendation about the source file that I could modify to achieve this (NOTE: I know that I don't have to modify directly the source file, instead I have to copy this in my SourceMods/ directory. Beforehand, I would greatly appreciate your recommendation.
 

slevis

Moderator
Staff member
I will suggest a process that you could try, same as what I would try myself, since I do not remember this information off the top of my head:
1) I would find relevant documentation in the Technical Note and/or in CLM articles; I recommend visiting the Technical Note first, because it documents everything about the model
2) Then I would search the code for key words and/or variable names corresponding to what I'm looking for; typically variable names are more descriptive than the scientific symbols used in Technote equations, but this step may take some detective work
3) Then, as you said, copy the .F90 files to /SourceMods and start modifying the code
 
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paulino

Paulino Ajiquichi
New Member
Dear Slevis

Thank you very much for the recommendation. I have reading the documentation and I found something about friction velocity (ustar) which is related with surface drag. My goal now is try to increase by 2 the friction velocity for certain grid cells over North Africa. I am working with CESM2.1.5, and I checked the source files. I found FrictionVelocityMod.F90 file which contains the subroutine FrictionVelocity (I attach an screenshot).

I am trying to understand how the model works, so I ran some cases to see how ustar is computed and I noticed that it is only computed for certain grid cells ( I attach an screenshot of then lnd.log file). The loop that appear in the subroutine to compute ustar depends on "fn" which is the filtered land unit elements. I am a beginner, so I am not sure exactly if this is the correct place/file to make the changes or if there is another file which I have to modify first. I have a list of target grid cells over North Africa, but as I said must of this grid cells are not used to computed ustar so I am not able to make the change in these grid cells. I would greatly appreciate any suggestion.

NOTE: it seems that the value of fn depens a bit on the component set. For the screenshots that I attached I used: HIST_CAM60_CLM50%BGC-CROP_CICE_POP2%ECO%ABIO-DIC_MOSART_CISM2%NOEVOLVE_WW3_BGC%BDRD
 

Attachments

  • FrictionVelocity.png
    FrictionVelocity.png
    99.5 KB · Views: 2
  • lnd-log.png
    lnd-log.png
    129.8 KB · Views: 2
  • subroutineFrictionVelocity.png
    subroutineFrictionVelocity.png
    63.2 KB · Views: 2
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oleson

Keith Oleson
CSEG and Liaisons
Staff member
FrictionVelocity is called by the various surface flux routines (call FrictionVelocity):

BareGroundFluxesMod.F90
UrbanFluxesMod.F90
CanopyFluxesMod.F90
LakeFluxesMod.F90

so I would expect that all gridcells and landunits and/or patches should have a calculation of ustar.
Another approach in the literature to represent wind farms is to modify roughness length and displacement height for those gridcells/surface types. This is the so-called Z0 approach in this CAM/CLM paper:


These roughness lengths and displacement heights are set in CanopyTemperatureMod.F90. This would then affect the ustar calculation.
 
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