cam6_4_019: New CLUBB External to fix GPU problem

[Katetc]

Small answer changes, but no new CLUBB science. Diagnostics can be found here: https://webext.cgd.ucar.edu/F2000climo/newCLUBBtesting/larson_tag_20240605.katemerge.062724-0201.F2000dev.f09_f09_mg17_1_2_vs_larson_tag_control.cam6_3_162.062724-1359.F2000dev.f09_f09_mg17_1_2/website/index.html

Ran 6 year ne30 BLT1850 simulations to look at differences in applicable and longer runs. Had some trouble with diagnostics but the results can be found here: https://webext.cgd.ucar.edu/FHIST/clubb_tests/larson_tag_20240605.katemerge.071924-1633.FLTHIST.ne30pg3_g17_1979_1984_vs_larson_tag_control.cam6_4_007.071924-1639.FLTHIST.ne30pg3_g17_1979_1984/website/

Differences seem to be minimal.

Fixes #1036

[adamrher]

@Katetc I'm under the impression that these new clubb externals remove the ghost point from the thermodynamic 'zt' grid. But I'm not seeing a reduction in the size of the zt arrays in clubb_intr in this PR. What am I missing?

[cacraigucar]

@adamrher and @bstephens82 - @Katetc requested reviews from both of you. Please either remove yourself as a reviewer or do a review when you can.

[vlarson]

I'm approving this PR, but would like to understand why all the arrays on the thermodynamic grid in clubb_intr.F90 are still retaining their ghost points. It was my understanding that this PR is removing the ghost point? Is the plan to just do that in the clubb externals, not the CAM interface?

For example, rho_zt is still of size dimension(state%ncol,pverp+1-top_lev) in clubb_intr.F90; it has the ghost point.

This code merely changes some lower BCs to one-sided derivatives within CLUBB core (and fixes some minor bugs involving full-level variables being placed on the wrong (half-level) grid levels). This PR doesn't change the clubb_intr, but UWM hopes to do that at some point.

[vlarson]

@adamrher, do you think that the changes in the solution look "large", or do they look like what you'd expect from truncation error (numerics)?

[adamrher]

Thanks for getting back to me on the ghost point. All is good then.

@adamrher, do you think that the changes in the solution look "large", or do they look like what you'd expect from truncation error (numerics)?

The global mean turbulent fluxes and radiative fluxes look ~identical, so that suggests round-off level changes. There's some differences in the lat-lon map plots but those are what you would expect from comparing to two, 2 year long runs.

[Katetc]

One minor tweak requested, but I am approving

I had a minor bug fix too, so I fixed this "if" statement as well.