Bathymetry in s-coordinate OVERFLOW test cases

Context

The s-coordinate variants of the SETTE OVERFLOW test-case runs (EXP-sco_FCT2_flux_cen-ahm1000, EXP-sco_FCT2_flux_ubs, EXP-sco_FCT4_flux_cen-ahm1000, and EXP-sco_FCT4_flux_ubs) fail when using the current NEMO branch_4.2 version. When compiled with debug compiler options, these runs fail due to a floating-point exception raised during the computation of the horizontal momentum-flux divergence (in subroutines dyn_adv_cen2 and dyn_adv_ubs in the cen and ubs configurations, respectively).

Analysis

The definition of the vertical scale factors on the U-grid for the s-coordinate OVERFLOW configurations appears to be incompatible with the current OVERFLOW domain setup.

Fix

Bringing the computation of the OVERFLOW bathymetry at U-grid locations in file tests/OVERFLOW/MY_SRC/usrdef_zgr.F90 of NEMO branch_4.2 in line with the corresponding implementation in NEMO main may be suitable to resolve this issue.