Revision of SETTE PHYOPTS test-case variants

Context

Several of the PHYOPTS test-case variants, which are routinely run as part of the SETTE tests, currently fail. This includes the EXP-FCT2_flux_cen2, the EXP-FCT2_vect_{eenH,een,ene} and all of the EXP-FCT4_* LOCK_ECHANGE test-case variants when using the current NEMO main and branch_4.2 version, as well as the EXP-zps_FCT2_flux_ubs and all of the EXP-sco_* OVERFLOW test-case configurations of NEMO branch_4.2.

Analysis

The current failures of the LOCK_EXCHANGE test-case runs appear to be due to an outdated variable name used in the corresponding namelist input files; the EXP-zps_FCT2_flux_ubs test case appears to be numerically unstable; and the failure of the s-coordinate versions of the OVERFLOW test-case variants has been reported previously, see issue #255 (closed).

Fix

The obsolete variable name used in some LOCK_EXCHANGE test-case configurations is nn_een_e3f (in namelist group namdyn_vor); it seems to be possible to replace the corresponding entries by nn_e3f_typ = 0, in both the NEMO main and branch_4.2 versions of the affected test configurations. While the EXP-zps_FCT2_flux_ubs test case can apparently be stabilised by increasing the minimum permitted vertical grid-cell extent defined as variable ze3min in file tests/OVERFLOW/MY_SRC/usrdef_zgr.F90 (e.g., an increase from 10% to 15% of the default scale factor appears to be sufficient), the precise cause of the failure, however, is currently unknown and remains to be tracked down. Further, the s-coordinate variants of the OVERFLOW test case should be addressed in the context of issue #255 (closed).