Change units of slope returned from calc_isoneutral_slopes() to "Z L-1" #1351
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Codecov Report
@@ Coverage Diff @@
## dev/gfdl #1351 +/- ##
=========================================
Coverage 45.83% 45.83%
=========================================
Files 234 234
Lines 72663 72663
=========================================
Hits 33302 33302
Misses 39361 39361
Continue to review full report at Codecov.
|
| real, dimension(SZIB_(G),SZJ_(G),SZK_(GV)+1), & | ||
| optional, intent(inout) :: N2_u !< Brunt-Vaisala frequency squared at | ||
| !! interfaces between u-points [T-2 ~> s-2] | ||
| real, dimension(SZI_(G),SZJB_(G),SZK_(GV)+1), & | ||
| optional, intent(inout) :: N2_v !< Brunt-Vaisala frequency squared at | ||
| !! interfaces between u-points [T-2 ~> s-2] | ||
| !! interfaces between v-points [L2 Z-2 T-2 ~> s-2] |
There was a problem hiding this comment.
I agree with this change, but for consistency there also has to be an equivalent change to the documented units of N2_u 3 lines above this change.
There was a problem hiding this comment.
Good spot - this was due to conflicts when I cherry-picked this out of my other branch
There was a problem hiding this comment.
I did a force push to avoid new commits.
- Units of isoneutral or interface slope were recorded as "nondim". While
true in SI units, not so for MOM6 units. MOM6 distinguishes between units
of length in the vertical (Z) and horizontal (L) the slopes should have
units of "Z L-1 ~> nondim".
- This has consequences for other variables in calc_isoneutral_slopes().
- An internal constant, G_Rho0, was defined differently from elsewhere in
the code. "g" has units of "L2 Z-1 T-2 ~ m s-2" because it is the
vertical component of the gradient of geopotential in "L2 T-2 ~ m2 s-2".
Everywhere else `G_Rho0 = g_Earth/Rho0` but in this routine it was
different in order render N2 (the Brunt-Vaisala frequency) in units of
"T-2" (s-2).
- N2 is a quantity associated with dispersion relations and defined
N2 = - g/Rho0 d/dz rho and either way acquires units of "L2 Z-2 T-2"
and not just "T-2". In SI units L2 Z-2 = 1. So I have also changed
the units of N2 in this, and connected, modules.
- The changes also propagate to MOM_lateral_mixing_coeffs.F90 and
MOM_thickness_diffuse.F90.
- Changing the definition of G_Rho0 in calc_isoneutral_slopes(), and
its units to "L2 Z-1 T-2", the slope and N2 calculations then require
many less inline conversions. Many of the one-line changes in this commit
remove factors like US%Z_to_L.There is one exception:
- In the calculation of slope, we use in the denominator a mostly
non-vanishing replacement for d/dz rho, the magnitude of grad rho from
mag_grad2 = ( d/dx rho )^2 + ( d/dz rho )^2. In code this had
`mag_grad2 = drdy**2 + (L_to_Z*drdz)**2` since this is mixing
gradients in the horizontal and vertical. The result should be
in "R2 Z-2" so now `mag_grad2 = (Z_to_L*drdy)**2 + drdz**2`
- A few diagnostics needed new, or changed, conversion factors.
- One run-time parameter needed a conversion parameter.
- For the most part this commit moves inline conversions of units to
the I/O stage, which is an indicator that it is the right thing to do.
marshallward
approved these changes
Mar 12, 2021
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
This addresses the units of interface slope, or isoneutral slope, used for parameterizing thickness transport. I came across this while fixing the Eady growth rate calculation which will come next and depends on this PR but for the sake of smaller PRs am submitting them as a dependent sequence.
From the commit message:
G_Rho0 = g_Earth/Rho0but in this routine it was different in order render N2 (the Brunt-Vaisala frequency) in units of "T-2" (s-2).mag_grad2 = drdy**2 + (L_to_Z*drdz)**2which is mixing gradients in the horizontal and vertical. The result should be in "R2 Z-2" so nowmag_grad2 = (Z_to_L*drdy)**2 + drdz**2