Need and use of skin temperature

[doblerone]

To make gl working in the current setup, skin temperature needs to be provided.

Within gl, skin temperature is then used in util/gl_grib_api/ala/merge_ifs.f90 to replace SST values < 272.16 with surface temperature (kts) to have more realistic temperatures over ice:
IF ( adjust_sst_under_ice ) THEN
WHERE( ABS(ifsfld(1:intpgeo%nlon,1:intpgeo%nlat,ksst)-missing_data) > 1._jprb .AND. &
ifsfld(1:intpgeo%nlon,1:intpgeo%nlat,ksst) < 272.16_jprb )
ifsfld(1:intpgeo%nlon,1:intpgeo%nlat,ksst) = &
ifsfld(1:intpgeo%nlon,1:intpgeo%nlat,kts )
END WHERE
ENDIF

However, in Interpol_sst_sic there is
if [ $SURFEX_SEA_ICE = "sice" ] ; then ADJUST_SST_UNDER_ICE=.FALSE.; else ADJUST_SST_UNDER_ICE=.TRUE. fi
and we use $SURFEX_SEA_ICE = "sice"

Thus, surface temperature is not used and we can provide it for all time steps (as far as I can see) without really using it.

Issue: needs to be checked.