A Heton Perspective of Baroclinic Eddy Transfer in Localized Open Ocean Convection

Legg, Sonya; Jones, Helen; Visbeck, Martin

doi:10.1175/1520-0485(1996)026<2251:ahpobe>2.0.co;2

Cited by 51 publications

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“…The integrated properties of a convective patch can be characterized in terms of an unstably stratified volume undergoing rapid vertical mixing (Send and Marshall 1995). Numerical experiments suggest that such a mixed patch exchanges buoyancy with its stratified surroundings, both during and after convection, through baroclinic instability and the shedding of hetons (Legg et al 1996). Figure 2 is a schematic representing the processes that lead to the formation and propagation of a heton.…”

Section: Background To the Dynamics Of Postconvective Vortices A Hetmentioning

confidence: 99%

“…At the instant of formation, a heton is a vertically aligned dipole, consisting of a cyclone directly overlying an anticyclone. This may be understood in terms of the redistribution of potential vorticity (Legg and Marshall 1993) or in terms of geostrophic shear: the weakly stratified heton is a buoyant anomaly at depth, causing anticyclonic shear, and a dense anomaly at the surface, causing cyclonic shear.…”

Section: Background To the Dynamics Of Postconvective Vortices A Hetmentioning

confidence: 99%

“…2c lies to the left of the subsurface anticyclone, causing self-propogation into the page. The name "heton" derives from the heat transport associated with this self-propagation (Hogg and Stommel 1985), and the theory describing the behavior of hetons in a rotating uniformly stratified fluid is well developed (e.g., Griffiths and Hopfinger 1986;Legg and Marshall 1993;Carton 2001). Gryanik et al (2000) developed a quasigeostrophic theory for isolated hetons, with equal magnitude cyclonic and anticyclonic components, in uniform stratification and zero ambient shear.…”

Section: Background To the Dynamics Of Postconvective Vortices A Hetmentioning

confidence: 99%

“…It is unusual to observe ongoing deep convection, and the majority of evidence for convection is obtained from observing postconvective vortices (Kasajima et al 2006), or regional-scale stratification (Ronski and Budeus 2005), weeks or months after convection has ceased. Moreover, the postconvective behavior of vortices is likely to be a key control on the heat and salinity budgets of convective regions (Legg et al 1996). Postconvective dynamics have been the focus of previous process studies (e.g., Legg and Marshall 1998;Gryanik et al 2000), but these have been in the context of a uniform ambient hydrography.…”

Section: Introductionmentioning

confidence: 99%

“…Moreover, the postconvective behavior of vortices is likely to be a key control on the heat and salinity budgets of convective regions (Legg et al 1996). Postconvective dynamics have been the focus of previous process studies (e.g., Legg and Marshall 1998;Gryanik et al 2000), but these have been in the context of a uniform ambient hydrography. In practice, convection occurs in cyclonic gyres with significant horizontal density gradients and bounded by steep topography, each of which has the potential to influence the behavior of postconvective vortices.…”

Section: Introductionmentioning

confidence: 99%

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A Greenland Sea Perspective on the Dynamics of Postconvective Eddies*

Oliver

Eldevik

Stevens

et al. 2008

Journal of Physical Oceanography

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Open ocean deep postconvection contributes to the formation of the dense waters that fill the global deep ocean. The dynamics of postconvective vortices are key to understanding the role of convection in ocean circulation. Submesoscale coherent vortices (SCVs) observed in convective regions are likely to be the anticyclonic components of hetons. Hetons are dipoles, consisting of a surface cyclone and a weakly stratified subsurface anticyclone, that can be formed by convection. Here, key postconvective processes are investigated using numerical experiments of increasing sophistication with two primary goals: 1) to understand how the ambient hydrography and topography influence the propagation of hetons and 2) to provide a theoretical context for recent observations of SCVs in the Greenland Sea.It is found that the alignment of hetons is controlled by ambient horizontal density gradients and that hetons self-propagate into lighter waters as a result. This provides a mechanism for transporting convected water out of a cyclonic gyre, but the propagation is arrested if the heton meets large-amplitude topography. Upon interaction with topography, hetons usually separate, and the surface cyclone returns toward denser water. The anticyclone usually remains close to topography and may become trapped for several hundred days. These findings may explain the observed accumulation and longevity of SCVs at the Greenland Fracture Zone, on the rim of the Greenland Sea gyre. The separation and sorting of cyclones from anticyclones have likely implications for the density and vorticity budgets of convective regions.

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Section: Background To the Dynamics Of Postconvective Vortices A Hetmentioning

confidence: 99%

Section: Background To the Dynamics Of Postconvective Vortices A Hetmentioning

confidence: 99%

Section: Background To the Dynamics Of Postconvective Vortices A Hetmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

A Greenland Sea Perspective on the Dynamics of Postconvective Eddies*

Oliver

Eldevik

Stevens

et al. 2008

Journal of Physical Oceanography

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Modeling Postconvective Submesoscale Coherent Vortices in the Northwestern Mediterranean Sea

et al. 2017

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For the first time, the formation of submesoscale coherent vortices (SCVs) during intermediate and deep convection events is documented in a realistic high‐resolution (1 km) numerical simulation of the oceanic circulation in the northwestern Mediterranean Sea. Winter intermediate and deep convection leads to the formation of anticyclonic and cyclonic eddies with lifetimes exceeding 1 year. By focusing on three typical eddies, the main characteristics of such vortices are discussed. The anticyclonic eddies are typical of SCVs observed in deep convection areas so far. They are characterized by a small radius (∼6.5 km) and orbital peak velocities of about 7 cm/s located at great depth (∼1500 m) or intermediate depth (∼500 m). The cyclonic vortices show very similar characteristics, such as a high Rossby number (∼0.4), but with surface‐intensified structures. The long lifetimes of both anticyclonic and cyclonic eddies reflect very slow diffusive processes between their core and their surroundings and a strong resistance to external perturbations. These long‐lived eddies are found to participate in the spreading of a significant portion (from 15 to 35%) of the convected waters in the Gulf of Lions and contribute to the ventilation of the deep basin.

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Scales and dynamics of Submesoscale Coherent Vortices formed by deep convection in the northwestern Mediterranean Sea

et al. 2016

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Since 2010, an intense effort in the collection of in situ observations has been carried out in the northwestern Mediterranean Sea thanks to gliders, profiling floats, regular cruises, and mooring lines. This integrated observing system enabled a year‐to‐year monitoring of the deep waters formation that occurred in the Gulf of Lions area during four consecutive winters (2010–2013). Vortical structures remnant of wintertime deep vertical mixing events were regularly sampled by the different observing platforms. These are Submesoscale Coherent Vortices (SCVs) characterized by a small radius (∼5–8 km), strong depth‐intensified orbital velocities (∼10–20 cm s−1) with often a weak surface signature, high Rossby (∼0.5) and Burger numbers O(0.5–1). Anticyclones transport convected waters resulting from intermediate (∼300 m) to deep (∼2000 m) vertical mixing. Cyclones are characterized by a 500–1000 m thick layer of weakly stratified deep waters (or bottom waters that cascaded from the shelf of the Gulf of Lions in 2012) extending down to the bottom of the ocean at ∼2500 m. The formation of cyclonic eddies seems to be favored by bottom‐reaching convection occurring during the study period or cascading events reaching the abyssal plain. We confirm the prominent role of anticyclonic SCVs and shed light on the important role of cyclonic SCVs in the spreading of a significant amount (∼30%) of the newly formed deep waters away from the winter mixing areas. Since they can survive until the following winter, they can potentially have a great impact on the mixed layer deepening through a local preconditioning effect.

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A Heton Perspective of Baroclinic Eddy Transfer in Localized Open Ocean Convection

Cited by 51 publications

References 0 publications

A Greenland Sea Perspective on the Dynamics of Postconvective Eddies*

A Greenland Sea Perspective on the Dynamics of Postconvective Eddies*

Modeling Postconvective Submesoscale Coherent Vortices in the Northwestern Mediterranean Sea

Scales and dynamics of Submesoscale Coherent Vortices formed by deep convection in the northwestern Mediterranean Sea

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