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It is well understood that isolated eddies are presumed to propagate westward intrinsically at the speed of the annual baroclinic Rossby wave. This classic description, however, is known to be frequently violated in both propagation speed and its direction in the real ocean. Here, we present a systematic analysis on the divergence of eddy propagation direction (i.e., global pattern of departure from due west) and dispersion of eddy propagation speed (i.e., zonal pattern of departure from Rossby wave phase speed). Our main findings include the following: 1) A global climatological phase map (the first of its kind to our knowledge) indicating localized direction of most likely eddy propagation has been derived from 28 years (1993–2020) of satellite altimetry, leading to a leaf-like full-angle pattern in its overall divergence. 2) A meridional deflection map of eddy motion is created with prominent equatorward/poleward deflecting zones identified, revealing that it is more geographically correlated rather than polarity determined as previously thought (i.e., poleward for cyclonic eddies and equatorward for anticyclonic ones). 3) The eddy–Rossby wave relationship has a duality nature (waves riding by eddies) in five subtropical bands centered around 27°N and 26°S in the two hemispheres, outside which their relationship has a dispersive nature with dominant waves (eddies) propagating faster in the tropical (extratropical) oceans. Current, wind, and topographic effects are major external forcings responsible for the observed divergence and dispersion of eddy propagations. These results are expected to make a significant contribution to eddy trajectory prediction using physically based and/or data-driven models. [ABSTRACT FROM AUTHOR]

Systematic eddy propagation with a westward dominance is a well-documented feature in the global ocean, thanks to the availability of constellated altimeter measurement of sea level anomaly with a centimeter-level accuracy. According to their zonal speed relative to the phase speed of the first baroclinic Rossby wave, we propose that eddies can be divided into two modes: "eddy trains" and "eddy jets". The former refers to isolated eddies intrinsically guided by the long Rossby wave theory in zonal propagation, meanwhile significantly advected by energetic extratropical currents (via Doppler-like effect) and equatorial planetary waves (basically Kelvin waves). The latter refers mostly to "geared" eddy dipoles (also known as "modons" governed by the equivalent barotropic vorticity equation) that propagate with a "super" speed escaping from the Rossby wave guide. In this study, departure and reversal of eddy trains from the Rossby theory are analyzed and compensated, meanwhile the signature and mechanism of eddy jets are identified and revealed. As a result, three distinct regimes are observed in oceanic eddy propagation: A primary Rossby regime (∼66%, westward), a secondary anti-Rossby regime (∼33%, eastward, modulated by Doppler-like and Kelvin wave effects), and a third minor non-Rossby regime (∼1%, zonally neutral, of dipolar nature with gear effect). The first two regimes combine to form the eddy trains, while the third regime belongs to the eddy jets. A clear understanding of the mechanism and pattern of the complex eddy propagations is critical to marine science in general, and to eddy science in particular. • Eddies can be intrinsically divided into two regimes: "eddy trains" and "eddy jets". • "Eddy trains" refer to isolated eddies guided by the long Rossby wave theory. • "Eddy jets" refer to "geared" dipolar eddies propagating with a super speed. [ABSTRACT FROM AUTHOR]

Mesoscale eddies exist throughout the global ocean and significantly impact local vertical marine stratification through the physical processes of stirring and pumping. While the vertical transportation dynamics of eddies are known, the contribution to the displacement of pycnocline depth from eddies has not been comprehensively investigated. In this study, the 17-year Argo dataset and satellite altimetry data are used to estimate the deepening and uplifting of the pycnocline depth induced by anticyclonic eddies (AE) and cyclonic eddies (CE), respectively. Pycnocline displacements exhibit multiple geographic and seasonal trends, with the largest magnitude occurring in spring. More pronounced displacements are concentrated in mid-latitudes, particularly along the western boundary currents, with peak displacements reaching more than 90 m. Furthermore, these displacements are positively correlated with eddy properties (particularly eddy amplitude), suggesting that higher intensity eddies may induce larger pycnocline displacements. In the eddy coordinate system, the pycnocline displacement reveals a monopole structure with a marked extremum in the eddy centre. At the eddy core, maximum deepening in AE reaches ~54 m in spring, but only ~25 m in autumn. In contrast, uplifting in CE reaches ~66 m (~18 m) in spring (autumn). The eddy-induced pycnocline displacements reported here emphasize the intrinsic vertical dynamics of eddies during oceanic observations and provide a pathway to reproduce the effects of eddies on variations of the pycnocline in ocean models. • The role of eddy on the pycnocline depth variation is quantitatively estimated. • Anticyclonic and cyclonic eddy are observed to deepen and uplift the pycnocline. • Larger pycnocline displacement is found in areas with energetic eddies in spring. • The displacement is symmetrically distributed in the eddy coordinate system. [ABSTRACT FROM AUTHOR]