Meridional Turner angles and density compensation in the upper ocean
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The World Ocean Atlas 1998 is used to determine the global field of the meridional density ratio Rρhy=αΔT/βΔS, where temperature and salinity changes ΔT and ΔS are evaluated along meridians, in and below the mixed layer. The focus of the analysis is the identification of regions where the Rρhy field matches the values Rρ=2 sometimes suggested as the commonly perceived state of the ocean and Rρ=1, the condition of density compensation. Results are presented through fields of the meridional Turner angle Tuhy=arctan(Rhyρ) and through histograms of Tuhy for the Pacific, Atlantic and Indian Oceans at the ocean surface and at 300 m depth. At the 300-m depth level, which in the subtropics is representative of conditions in the permanent thermocline, the most frequently encountered values of the meridional density ratio are Rρhy=3.2 in the North and South Pacific, Rρhy=2.0 in the South Atlantic and Indian and Rρhy=1.6 in the North Atlantic Ocean. Conditions in the mixed layer are more variable and show seasonal differences, but Rρhy=2.0 occurs prominently in all ocean regions during winter and in all regions but the Atlantic during summer. Summer values for the Atlantic Ocean are Rρhy=3.2 in the Northern Hemisphere and Rρhy=2.4 in the Southern Hemisphere. Detailed analysis of Rρhy across the Subtropical Front (STF) confirms the most frequently observed values but shows zonal variation along the front in some oceans. Nearly complete density compensation (Rρhy=1) in the mixed layer is encountered in the STF of the eastern North Pacific, the eastern South Pacific and the eastern Indian Ocean. The eastern Indian Ocean south of Australia is also the only region where complete density compensation in the STF occurs below the mixed layer.
KeywordsTurner angle Density compensation Subtropical front
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