Hydraulic Control And Turbulent Mixing Of Deep Overflows In Key Passages Of The Indonesian Seas And Pacific Ocean

The hydraulics,instability,and mixing of two deep strait flows are investigated theoretically and numerically based on observation,in an attempt to provide insights into understanding the influence of topography on the deep circulation and on the spatial distribution of mixing.The two study subjects include the deep branch of Indonesian Throughflow(ITF)passing the Lifamatola Passage and the Antarctic Bottom Water(AABW)entering the Samoan Passage.Historical mooring and recently obtained in-situ hydrographic observations suggest that the Lifamatola Passage overflow is hydraulically controlled,based on which various“weir”formulae(i.e.,estimating volume transport from stratification for cross-sections in different shapes)for non-rotating strait flows are employed and validated by observation.Hydraulic jump-like features,intense mixing,and entrainment(transport of 0.6-1.2 Sv)due to the presence of a hydraulically controlled overflow(transport of 2.4 Sv)are found in the lee of the sill.Thorpe-scale based estimates of diapycnal diffusivity coefficients averaged over downstream sites range from 2.3×10^*+m^-s^*/to 10.1×10^*+m^-s^*/within the overflow layer.The knowledge of strait flow transport and potential enthalpy flux allows estimating a bulk diapycnal diffusivity coefficient(1.6±0.5×10^*+m^-s^*/)in a closed basin downstream(i.e.,Banda Sea).The critical condition for rotating strait flows with uniform potential vorticity(i.e.,an extension to Gill,1977)are derived to predict the volume flux through multiple passages,at least one of which is located on the pathway of an ocean boundary current.The formulations have been applied to predicting the transport distribution of the Deep Western Boundary Current(DWBC)within the Samoan Passage and east of the Manihiki Plateau.However,these formulae are valid only when the throughflow(e.g.,flow through the Samoan Passage)is hydraulically controlled while the bypass flow(e.g.,flow to the east of the Manihiki Plateau)is uncontrolled.Such a steady state is possible if,along the plateau,the energy dissipation due to hydraulic jumps in the passage can be balanced by the dissipation due to viscous forces(e.g.,bottom frictions)in the bypass flow.