![]() Properties of this surface-intensified regime involve a velocity spectrum with a k −2 slope (instead of a k −3 slope for the Phillips regime). The resulting mesoscale turbulent regime is known as the Charney-like regime 5, 15 (after the original work of Charney 16). ![]() This interpretation invokes the instability derived from the interaction between the large-scale positive QGPV gradient in the upper layers (induced by large-scale surface density anomalies) and the negative QGPV gradient in the interior. Idealized modelling studies of the last 8 years 2, 11, 12, 13, 14, 15 led to the proposition of an alternative interpretation. This questioned the paradigm related to the Phillips regime. However, recent reanalysis of satellite altimeter and in situ data 7, 8, 9, 10 have pointed out that submesoscales are much more energetic than expected in many regions of the oceans, involving a k −2 spectrum slope over a large range of scales, which suggests an impact of these small scales on larger scales. In this regime, smaller-scale structures (O(1–50 km)), also called submesoscales, are therefore very weakly energetic and have little impact on mesoscale eddies, except in terms of KE dissipation. The resulting mesoscale turbulent dynamics is referred to as the Phillips regime 5 (after the seminal work of Phillips 6 related to baroclinic instability in the ocean interior) and leads to a velocity spectrum with a k −3 slope, with k being the wavenumber. Such instability occurs when the sign of QGPV horizontal gradients changes with depth and related studies showed that this depth is around 800–1,000 m. Until recently, the broadly accepted paradigm is that these eddies are generated and sustained by the instability of the large-scale vertical current shear (or horizontal gradient of quasigeostrophic potential vorticity (QGPV)) in the ocean interior. KE associated with mesoscale eddies is monitored from space by satellite altimeters and these eddies are also explicitly resolved in present-day realistic ocean numerical simulations. Oceanic eddies (100–300 km), also called mesoscale eddies, are known to explain not only most of the total kinetic energy (KE) in the oceans 1, but also most of the turbulent dispersion and transport of tracers such as heat and carbon dioxide in oceanic basins 1, 2, 3, 4. As such, it is driven by nonlinear scale interactions that can transfer energy upscale or downscale. These rifts are about 20 miles wide (30 km) and 6,500 feet (2,900 m) deep and are a site where lava is expelled on to the ocean floor.The oceanic flow is known to be highly turbulent involving a very broad range of scales from O(1,000 km) down to O(1 m) and even smaller scales 1. At the crest of the ridge system lies a trough or rift. Known for over a century, the mid-ocean ridge system in the Atlantic Ocean rises some 6,500 feet above the surrounding ocean floor and extends for more that 37,500 miles (60,000 km) in all the world's oceans. During the 1950's seismologists showed that earthquake activity was concentrated along the longest continuous mountain system on Earth, the mid-ocean ridge. ![]() In the late 1950's and early 1960's oceanographic research was opening the final frontier on Earth, the mysteries of the ocean floor. \): Mid-ocean Ridge (Courtesy USGS) (Click image to enlarge)
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