Salinity Boundary Conditions and the Atlantic Meridional Overturning Circulation in Depth and Quasi-Isopycnic Coordinate Global Ocean Models
NAVAL RESEARCH LAB STENNIS SPACE CENTER MS
Pagination or Media Count:
This paper compares the Atlantic Meridional Overturning Circulation AMOC in global simulations performed with the depth coordinate Parallel Ocean Program POP ocean model and with the HYbrid Coordinate Ocean Model HYCOM under different surface salinity boundary conditions. When forced by the Coordinated Ocean-ice Reference Experiment CORE repeat Normal Year Forcing, HYCOM develops internal inter-annual variability during the model spin-up, while POP does not and HYCOM is more sensitive to the salinity boundary condition in the Southern Ocean. Otherwise the AMOC and related fields in the two models are qualitatively similar, but neither is able to maintain a non-trivial AMOC, because of a positive feedback that continually freshens the high-latitude surface waters. However, with salinity restoring at the ocean surface the AMOC becomes progressively stronger as the piston velocity is increased. The different restoring strategies in POP and HYCOM cause differences in the AMOC simulation. The components of the AMOC and closely related fields, including the oceanic deep convection, thermohaline fluxes, three dimensional currents, water mass distribution and overflows, are compared between the models with different salinity boundary conditions. The comparison provides insights on the models response and increases our understanding of ocean climate simulations. It also provides motivation for the future development of ocean climate models capable of simulating the AMOC more realistically.
- Physical and Dynamic Oceanography