Ocean‐Scale Interactions From Space

Abstract

Satellite observations of the last two decades have led to a major breakthrough emphasizing the existence of a strongly energetic mesoscale turbulent eddy field in all the oceans. This ocean mesoscale turbulence is characterized by cyclonic and anticyclonic eddies (with a 100‐ to 300‐km size and depth scales of ∼500–1,000 m) that capture approximatively 80% of the total kinetic energy and is now known to significantly impact the large‐scale ocean circulation, the ocean's carbon storage, the air‐sea interactions, and therefore the Earth climate as a whole. However, ocean mesoscale turbulence revealed by satellite observations has properties that differ from those related to classical geostrophic turbulence theories. In the last decade, a large number of theoretical and numerical studies has pointed to submesoscale surface fronts (1–50 km), not resolved by satellite altimeters, as the key suspect explaining these discrepancies. Submesoscale surface fronts have been shown to impact mesoscale eddies and the large‐scale ocean circulation in counterintuitive ways, leading in particular to up‐gradient fluxes. The ocean engine is now known to involve energetic scale interactions, over a much broader range of scales than expected one decade ago, from 1 to 5,000 km. New space observations with higher spatial resolution are however needed to validate and improve these recent theoretical and numerical results.

Dynamics of Mesoscale Eddies Interacting With a Western Boundary Current Flowing by a Gap

“…Future studies should include the interactions of multiple eddies with the WBC and consider the roles of the submesoscale variability. Recent studies on the interactions of the submesoscale variability with mesoscale and large‐scale circulation in the ocean seem to suggest the importance of such interactions (Klein et al, ; Sasaki et al, ; Su et al, ; Torres et al, ). In addition, the seasonally variable WBC and the South China Sea throughflow are shown to alter the WBC hysteresis strongly (Song et al, ), which will impact the WBC‐eddy interactions.…”

Energetic Submesoscale Dynamics in the Ocean Interior

“…1). This offset is key to the generation of submesoscale buoyancy fronts and filaments, because the strain field will then be able to stretch and compress these background anomalies (Klein et al 2019). These large-and mesoscale characteristics are common to the two other most energetic currents: the Kuroshio Extension (Sasaki et al 2014) and the Gulf Stream (Chassignet and Xu 2017).…”

“…Meso-and submesoscale turbulence is characterized by the spontaneous emergence of numerous small-scale filaments and vortices with a horizontal size of tens of kilometers (McWilliams 2016), not directly identifiable in SSH ( Fig. 1) but evident in tracer fields, such as the Ertel PV (Klein et al 2019).…”

“…The simulation includes energetic IGWs, comprising internal tides, near-inertial motions and a large IGWs continuum at higher frequencies. As such, it is essential to be able to disentangle them from balanced motions, that is, flows in thermal or gradient wind balance that encompass meso and submesoscales (Klein et al 2019).…”

“…Oceanic mesoscale and submesoscale turbulence has been extensively studied in the past decade (Klein and Lapeyre 2009;Mahadevan 2016;McWilliams 2016). Results emphasize the existence of submesoscale fronts (#50-km width), predominantly confined to the surface mixed layer (ML) and particularly energetic in winter when ML instabilities are active (Fox-Kemper et al 2008;Callies et al 2015).…”