Comparison of the Ocean Components POP2 and HYCOM in the Community Earth System Model (CESM) at High Resolution

As part of an effort to document the impact on CESM of an alternate vertical coordinate ocean model, the Hybrid Coordinate Ocean Model (HYCOM) was added to the CESM workflow. A 20-year 1/12º ocean and ice simulation CESM-HYCOM is compared to a 1/10º ocean and ice POP-CESM. Both simulations are coupled to 0.5º atmospheric and land components and POP2 is the default fixed vertical coordinate ocean component of CESM.

The global circulation is very similar between the two experiments, but slightly stronger in HYCOM with an average AMOC transport of 18Sv at 26ºN compared to 15Sv in POP2. The globally averaged drifts in temperature and salinity are found to be weaker in HYCOM when compared to POP2, even though HYCOM’s temperature drift extends to the whole depth of the ocean, while POP2’s drifts remain constrained to the upper 1000m. This is due to cooling in HYCOM at the bottom of the Southern Ocean in convection regions. Additional diagnostics will be presented and discussed such as transports (heat and volume) and sea-ice extents.