Abstract
AbstractMesoscale eddies are ubiquitous and energetic features in the ocean. Although eddies are known to form dipoles from time to time, it is unclear how often they do so. Using satellite altimetry data, here we show that mesoscale dipoles are surprisingly widespread in the global ocean. About 30–40% of the mesoscale eddies identified in altimeter data are paired up as dipoles, and the percentage is even higher in energetic regions such as the Gulf Stream and the Southern Ocean. Composite analysis involving Argo float data further reveals that these mesoscale dipoles have a relatively uniform three‐dimensional structure. We find that the presence of mesoscale dipoles can strongly enhance wind Ekman pumping velocity and lead to deep‐reaching vertical motions inside the dipoles via eddy deformation and frontogenesis. Such strong vertical exchanges promoted by mesoscale dipoles may play an important role in regulating the Earth's biogeochemical processes.
Highlights
Mesoscale eddies, accounting for the majority of the ocean's kinetic energy, play a vital role in transporting climatically important properties and tracers such as momentum, heat, carbon, and nutrients (Conway et al, 2018; Dong et al, 2014; Wunsch, 1999; Zhang et al, 2014)
In this study we have provided the first observational evidence to show that mesoscale dipoles are widespread features in the global ocean
The vertical velocity induced by the dipole structure is comparable in magnitude with those associated with other mesoscale and even some submesoscale physical processes (Gaube et al, 2015; Klein & Lapeyre, 2009; Mahadevan, 2016; Pascual et al, 2015)
Summary
Mesoscale eddies, accounting for the majority of the ocean's kinetic energy, play a vital role in transporting climatically important properties and tracers such as momentum, heat, carbon, and nutrients (Conway et al, 2018; Dong et al, 2014; Wunsch, 1999; Zhang et al, 2014). Theory predicts that mesoscale dipoles are the simplest dynamically consistent, and potentially ubiquitous, features in the ocean (Flierl et al, 1983). Mesoscale eddy dipoles have been observed a number of times near the eastern boundary (Ahlnäs et al, 1987; Callendar et al, 2011; Pidcock et al, 2013; Simpson & Lynn, 1990) and in association with the western boundary currents (de Ruijter et al, 2004; Hooker et al, 1995). Via visual analysis, nine rapidly moving eddy dipoles were identified in satellite altimeter data in the midlatitude ocean to the north of the Antarctic Circumpolar Current (Hughes & Miller, 2017). The distribution and three‐dimensional (3‐D) structure of mesoscale dipoles remain unknown, especially on the global scale
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