+(*)Clarify turbulent energetics and add EPBL_BBL_TIDAL_EFFIC #808
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Jan 24, 2025
Revised the name of visc%TKE_BBL to visc%BBL_meanKE_loss to better reflect what these variables contain, and the fact that the efficiency of the conversion from mean kinetic energy loss to turbulent kinetic energy has not been applied yet. The units of visc%BBL_meanKE_loss are [H L2 T-3 ~> m3 s-3 or W m-2], whereas those of visc%TKE_BBL were [H Z2 T-3 ~> m3 s-3 or W m-2]. The factor rescaling between the units of mean kinetic energy and those of turbulent kinetic energy have been incorporated into set_diffusivity_CS%BBL_effic and energetic_PBL_CS%ePBL_BBL_effic. All answers are bitwise identical.
Revised the name of fluxes%TKE_tidal to fluxes%BBL_tidal_dis to better reflect what this field holds,and the fact that the efficiency of the conversion from mean kinetic energy loss to turbulent kinetic energy has not been applied yet. The units of fluxes%BBL_tidal_dis are [R Z L2 T-3 ~> W m-2], whereas those of fluxes%TKE_tidal were [R Z3 T-3 ~> W m-2]. The factor rescaling between the units of mean kinetic energy and those of turbulent kinetic energy were already in set_diffusivity_CS%BBL_effic, and these have been cancelled out by this change, but this is offset by the addition of rescaling factors in the term setting this array in the NUOPC and mct convert_IOB_to_fluxes routines. In the FMS_cap version of convert_IOB_to_fluxes, the extra rescaling factor is rolled into the scaling factor used in the get_param call for rho_TKE_tidal. All answers are bitwise identical, but there is a change in the name and rescaled units of an element of a transparent type.
Added the option to use the energy source in fluxes%BBL_tidal_dis to drive mixing in ePBL_BBL_column(), similarly to what is done in add_drag_diffusivity() and add_LOTW_BBL_diffusivity(). Because this was omitted when ePBL_BBL_column() was first added, a separate runtime parameter, EPBL_BBL_TIDAL_EFFIC, is used to determine the extent to which this tidal energy source is used. The default for EPBL_BBL_TIDAL_EFFIC is currently set to 0 to avoid changing answers, but perhaps it should be changed follow the value of EPBL_BBL_EFFIC. By default all answers are bitwise identical, but there is a new runtime parameter in the MOM_parameter_doc files for cases that use ePBL.
Previously, visc%BBL_meanKE_loss (which was called visc%TKE_BBL before it was renamed) was missing a factor of the square root of the drag coefficient compared with the net loss of kinetic energy. This was compensated for by multiplication by factors of the square root of the drag coefficient in add_drag_diffusivity and add_LOTW_BBL_diffusivity, but when an equivalent expression was added in the ePBL BBL code this was erroneously omitted. Moreover, Alistair has had a comment questioning this added factor in add_LOTW_BBL_diffusivity for a decade without adequate resolution. To correct this confusing situation, visc%BBL_meanKE_loss has been changed to include the missing factor of the square root of the drag coefficient, while the new variable visc%BBL_meanKE_loss_sqrtCd was added to allow for the previous answers to be recovered when the new runtime parameter EPBL_BBL_EFFIC_BUG is set to true and DRAG_DIFFUSIVITY_ANSWER_DATE is set below 20250302. Because the ePBL bottom boundary layer was only added to dev/gfdl a month ago and has not yet been merged into main, we can be confident that it has only received very limited use as yet, so the default for EPBL_BBL_EFFIC_BUG is false but this default will change answers when EPBL_BBL_EFFIC > 0. The default for DRAG_DIFFUSIVITY_ANSWER_DATE is 20250101, which will preserve the previous answers, but the default should later be taken from DEFAULT_ANSWER_DATE. By default, answers are unchanged in any cases that are more than a month old, but answers can change by default in a few very recent experiments. There are two new runtime parameters in some MOM_parameter_doc files.
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This PR has passed pipeline testing at https://gitlab.gfdl.noaa.gov/ogrp/mom6ci/MOM6/-/pipelines/26183 with the expected warnings about new runtime parameters. |
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This PR consists of 4 commits that make the purpose and nature of two fields in the forcing type and the
vertvisc_typeclearer, and also adds the option to use the dissipated tidal energy supplied via the fluxes type to drive mixing inePBL_BBL_column(). It also corrects a bug in the energy being used in the recently added ePBL BBL mixing.Visc%TKE_BBLhas been revised tovisc%BBL_meanKE_lossto reflect that this array contains the mean kinetic energy that has been extracted by the bottom drag, and that the efficiency has not yet been applied. The units were also changed from[R Z3 T-3 ~> W m-2]to[R Z L2 T-3 ~> W m-2], with the extra conversion factors to translate from the units of mean kinetic energy to those of turbulent kinetic energy folded intoset_diffusivity_CS%BBL_efficandenergetic_PBL_CS%ePBL_BBL_effic. Similarly,fluxes%TKE_tidalhas been renamed tofluxes%BBL_tidal_disand its units are changed to[R Z L2 T-3 ~> W m-2]to reflect that this is the mean kinetic energy that has been dissipated and that the fractional efficiency has not been applied yet.This PR also adds the option to use the energy source in
fluxes%BBL_tidal_disto drive mixing inePBL_BBL_column()has been added, with the new runtime parameterEPBL_BBL_TIDAL_EFFICto control how much mixing is applied. By default this parameter is set to 0 and all answers are bitwise identical.Finally, this PR corrects a confusing situation regarding the absence of a factor of the square root of the drag coefficient in
visc%TKE_BBL, which led to both a bug when it was used in the ePBL BBL mixing and the persistence of a comment about this confusion that had not been addressed in 10 years. To correct this confusing situation,visc%BBL_meanKE_lossincludes the missing factor of the square root of the drag coefficient, whilevisc%BBL_meanKE_loss_sqrtCdhas the same values as were previously invisc%TKE_BBLto allow for the previous answers to be recovered when the new runtime parameterEPBL_BBL_EFFIC_BUGis set to true andDRAG_DIFFUSIVITY_ANSWER_DATEis set below 20250302. Because the ePBL bottom boundary layer was only added to dev/gfdl a month ago and has not yet been merged into main, we can be confident that it has only received very limited use as yet, so the default forEPBL_BBL_EFFIC_BUGis false but this default will change answers whenEPBL_BBL_EFFIC > 0. The default forDRAG_DIFFUSIVITY_ANSWER_DATEis 20250101, which will preserve the previous answers, but the default should later be taken fromDEFAULT_ANSWER_DATE.All answers and output are bitwise identical by default in any cases that are more than a month old, but answers can change by default in a few very recent experiments. There are renamed and rescaled elements in two transparent types, and new entries in some MOM_parameter_doc files. The specific commits in this PR include: