Proposed minor updates to canopy biogeophysics diagnostic variables

[mpaiao]

I was going through the code to incorporate a few additional output variables in ELM based on the CLM code (E3SM-Project/E3SM#7328), and in the process I found the following:

1. The units and description of variable USTAR are incorrect. I guess the description should be friction velocity, and the units should be m/s.

CTSM/src/biogeophys/FrictionVelocityMod.F90

Lines 286 to 288 in e0104b9

	call hist_addfld1d (fname='USTAR', units='s/m', &
	avgflag='A', long_name='aerodynamical resistance ', &
	ptr_patch=this%ustar_patch, default='inactive')

2. A few lines later, variable VPD seems to be reported in Pa:

CTSM/src/biogeophys/FrictionVelocityMod.F90

Lines 314 to 316 in e0104b9

	call hist_addfld1d (fname='VPD', units='Pa', &
	avgflag='A', long_name='vpd', &
	ptr_patch=this%vpd_patch, default='inactive')

But the actual calculation has a factor of 0.001_r8, which seems to be a conversion factor to kPa.

CTSM/src/biogeophys/CanopyFluxesMod.F90

Lines 1103 to 1111 in e0104b9

	svpts(p) = el(p) ! pa
	eah(p) = forc_pbot(c) * qaf(p) / 0.622_r8 ! pa
	rhaf(p) = eah(p)/svpts(p)
	! variables for history fields
	rah1(p) = rah(p,above_canopy)
	raw1(p) = raw(p,above_canopy)
	rah2(p) = rah(p,below_canopy)
	raw2(p) = raw(p,below_canopy)
	vpd(p) = max((svpts(p) - eah(p)), 50._r8) * 0.001_r8

3. This one is just a very minor detail, but the term "Monin-Obukhov length" is incorrect, it should be "Obukhov length" according to the American Meteorological Society.

I have a commit ready for pull request that addresses all these points, but I am first opening an issue to see if there are any concerns with my suggested changes.

[olyson]

My 2 cents is that I agree with these changes. Thanks for finding these.
Regarding 2, it seem like the units on the associate statement would also need to be changed from Pa to kPa:

vpd => frictionvel_inst%vpd_patch , & ! Output: [real(r8) (:) ] vapor pressure deficit [Pa]

Regarding 3, Gordon Bonan's Ecological Climatology book refers to L as the Obukhov length scale, but Obukhov length seems fine also...

[mpaiao]

Thanks for the feedback @olyson! For 2, I wasn't sure if it would be preferable to update the units to kPa, or to make the output in Pa (and drop the 0.001_r8 factor). I guess the latter would not be bit-for-bit.

For 3, "Obukhov length scale" is fine, I can update my branch and push it.

[olyson]

Yeah, it would probably be better to be bit-for-bit in my opinion. We have a (relatively) fast-track bfb branch that these changes could go on.