Add Leith+E #251
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This commit adds the 2D Leith+E closure, which uses a modified 2D Leith biharmonic viscosity paired with a harmonic backscatter. ('Modified' here is not used in the same sense as 'modified 2D Leith'; it just means that the biharmonic coefficient is modified to account for enstrophy backscatter.) Variables are often named 'leithy' to refer to Leith+E.
The parameterization is controlled by three main entries in user_nl_mom:
1. USE_LEITHY = True
2. LEITH_CK = 1.0
3. LEITH_BI_CONST = 8.0
To use Leith+E you should have LAPLACIAN=True and BIHARMONIC=True. (It doesn't hurt to be explicit and also set LEITH_AH=False, along with any other viscous closures, but this is not required. If USE_LEITHY=True it will not use any of the other schemes. It does use the background value of the biharmonic coefficient as a minimum, but ignores the
background harmonic value.) LEITH_CK is the fraction of energy dissipated by the biharmonic term that gets backscattered by the harmonic term (it's a target; the backscatter rate is not exact.) Recommended values between 0 and 1. LEITH_BI_CONST is Upsilon^6 where Upsilon is the ratio between the grid scale and the dissipation scale for enstrophy.
Values should be greater than or equal to 1; 8 is a good place to start.
The code is sensitive to the background value of Ah; specifically, if Ah is too large, the code is unstable. This is because the backscatter coefficient is proportional to Ah, and if Ah is large then you get large backscatter. If your code is unstable, consider reducing, e.g., `AH_VEL_SCALE`.
Codecov ReportPatch coverage:
Additional details and impacted files@@ Coverage Diff @@
## dev/ncar #251 +/- ##
============================================
- Coverage 37.07% 37.02% -0.06%
============================================
Files 264 264
Lines 74421 74564 +143
Branches 13780 13813 +33
============================================
+ Hits 27592 27604 +12
- Misses 41739 41855 +116
- Partials 5090 5105 +15
☔ View full report in Codecov by Sentry. |
This commit updates the code so that it uses the background Ah as a minimum. Previously, if `SMAGORINSKY_AH = True`, Leith+E would use the Smag value of Ah as the minimum, which is incorrect.
mnlevy1981
pushed a commit
to mnlevy1981/MOM6
that referenced
this pull request
Aug 10, 2023
There are extra US%T_to_s scaling factors in the expressions for ustar_min that were recently introduced with dev/gfdl PR NCAR#251; these are duplicative of the scaling factor that is already being applied when the parameter OMEGA is read in. The resulting expressions for ustar_min therefore effectively have units of [Z s T-2 ~> m s-1] when they should have units of [Z T-1 ~> m s-1]. Because ustar_min is a tiny floor on the magnitude of ustar, there is a range of values of T_RESCALE_POWER that will give the same answers as when it is 0, but for large enough values the answers will change, perhaps dramatically. This small commit removes these extra factors. Answers will change for some large values of T_RESCALE_POWER, but they are bitwise identical in the TC testing and in MOM6-examples based regression tests with modest or negative values.
Removed `do_not_log` condition on `USE_LEITHY`
|
Just one more minor very minor suggestion. We should follow Fortran2003 conventions, so |
Added one line to fix the fact that the code would only work as intended if either (i) writing out Ah_h, or (ii) in debug mode. Also swapped .le. and .lt. for <= and <.
|
@iangrooms, thanks for addressing all the issues. |
gustavo-marques
approved these changes
Aug 29, 2023
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This commit adds the 2D Leith+E closure, which uses a modified 2D Leith biharmonic viscosity paired with a harmonic backscatter. ('Modified' here is not used in the same sense as 'modified 2D Leith'; it just means that the biharmonic coefficient is modified to account for enstrophy backscatter.) Variables are often named 'leithy' to refer to Leith+E.
The parameterization is controlled by three main entries in user_nl_mom:
To use Leith+E you should have LAPLACIAN=True and BIHARMONIC=True. (You should also be explicit and set LEITH_AH=False, along with any other viscous closures. Leith+E does use the background value of the biharmonic coefficient as a minimum, but ignores the background harmonic value.) LEITH_CK is the fraction of energy dissipated by the biharmonic term that gets backscattered by the harmonic term (it's a target; the backscatter rate is not exact.) Recommended values between 0 and 1. LEITH_BI_CONST is Upsilon^6 where Upsilon is the ratio between the grid scale and the dissipation scale for enstrophy. Values should be greater than or equal to 1; 8 is a good place to start.
The code is sensitive to the background value of Ah; specifically, if Ah is too large, the code is unstable. This is because the backscatter coefficient is proportional to Ah, and if Ah is large then you get large backscatter. If your code is unstable, consider reducing, e.g.,
AH_VEL_SCALE.