# drag coefficient in wrf

#### water

##### New member
When I do the ideal test to simulate a tropical cyclone, the roughness on land is a fixed value, but the drag coefficient is variable and can be up to = 0.1, is this normal?

CD is a function of wind speed. This result is reasonable.

CD is a function of wind speed. This result is reasonable.
Thank you! Where can I find the formula for calculating CD

It depends on the sfclay scheme. Which surface layer scheme did you use?

It depends on the sfclay scheme. Which surface layer scheme did you use?
I used Revised MM5.

The calculation of surface exchange coefficient is conducted in phys/module_sf_sfclayrev.F, in which you can find the folloiwng piece of code:
Code:
``````        IF(PRESENT(ck) .and. PRESENT(cd) .and. PRESENT(cka) .and. PRESENT(cda)) THEN

Ck(I)=(karman/psix10)*(karman/psiq10)

Cd(I)=(karman/psix10)*(karman/psix10)

Cka(I)=(karman/psix)*(karman/psiq)

Cda(I)=(karman/psix)*(karman/psix)

ENDIF``````

The calculation of surface exchange coefficient is conducted in phys/module_sf_sfclayrev.F, in which you can find the folloiwng piece of code:
Code:
``````        IF(PRESENT(ck) .and. PRESENT(cd) .and. PRESENT(cka) .and. PRESENT(cda)) THEN

Ck(I)=(karman/psix10)*(karman/psiq10)

Cd(I)=(karman/psix10)*(karman/psix10)

Cka(I)=(karman/psix)*(karman/psiq)

Cda(I)=(karman/psix)*(karman/psix)

ENDIF``````
Thank you very much for your help. I would also like to ask how to modify soil moisture availability profiles.

Thank you very much for your help. I would also like to ask how to modify soil moisture availability profiles.
Q2:I used Noah LSM, what are the heights of layers 0-3 in the variable SMOIS?