Performance with 0.25 degree ocean

[MartinDix]

For comparison, CM2 suite with 0.25 ocean (u-cz789) used

ATM_PROCX=24
ATM_PROCY=18
CICE_BLKX=15
CICE_BLKY=1080
CICE_COL=1440
CICE_MAXBK=1
CICE_ROW=1080
MOM_CPUS=618
MOM_PROCX=32
MOM_PROCY=24

The UM was reduced from the usual 576 PEs to 432 to better match the MOM time (note that they're running simultaneously with OASIS). CICE used 96, so 1146 total (rounded up to 1152).

UM, MOM and CICE time steps were all 1200 s. Atmosphere coupling every 3 hours.

Model took approx 170 minutes for each 6 month run, so approx 4 years/day.