Spontaneous Generation of Inertia–Gravity Waves during the Merging of Two Baroclinic Anticyclones

Pallàs‐Sanz, Enric; Viúdez, Álvaro

doi:10.1175/2007jpo3716.1

Cited by 11 publications

(3 citation statements)

References 37 publications

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“…Moreover, as the two vortices co-rotate, the IGWs spread away from the vortices in a spiral pattern. Similar spiral patterns have been observed by Viúdez (2006), Pallàs-Sanz & Viúdez (2008. The maximum imbalanced vertical velocities are found inside the vortex, in particular near their inner edges.…”

Section: Resultssupporting

confidence: 82%

The merger of geophysical vortices at finite Rossby and Froude number

Reinaud

Dritschel

2018

J. Fluid Mech.

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We investigate the merger of two co-rotating geophysical vortices at finite Rossby and Froude number. The initial conditions consist of two uniform potential vorticity vortices in near-equilibrium and in a nearly ‘balanced’ state (i.e. with negligible emission of inertia–gravity wave radiation). We determine the critical merger distance between the two vortices. This distance is found to increase with the magnitude of the Rossby number: intense cyclones or intense anticyclones are able to merge from further apart compared to weaker cyclones and anticyclones. Note that the Froude number is proportional to the Rossby number for the near-equilibrium initial conditions considered. The critical merging distance also depends on the sign of the potential vorticity anomaly, which is positive for ‘cyclones’ and negative for ‘anticyclones’. We show that ageostrophic motions occurring at finite Rossby number tend to draw cyclones together but draw anticyclones apart. On the other hand, we show that anticyclones tend to deform more, in particular when subject to vertical shear (as when the vortices are vertically offset). These two effects compete. Overall, nearly aligned cyclones tend to merge from further apart than their anticyclonic counterparts, while vertically offset anticyclones merge from further apart than cyclones.

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Section: Resultssupporting

confidence: 82%

The merger of geophysical vortices at finite Rossby and Froude number

Reinaud

Dritschel

2018

J. Fluid Mech.

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“…Moreover, cyclone-anticyclone asymmetry in IGWs from a corotating vortex pair has been recently found (Sugimoto et al 2015). This asymmetry was also reported by the numerical simulation of a vortex merger (Sugimoto 2015; note that Pallàs-Sanz and Viúdez (2008) investigated spontaneous IGW radiation in a vortex merger for the first time). However, since analytical derivation was performed only for an idealized case of a co-rotating point vortex pair, and numerical verifications were done for cases of a co-rotating vortex pair and its merger as a numerical extension, it is not evident whether this asymmetry appears in complicated vortical flows.…”

Section: Introductionsupporting

confidence: 60%

Inertia–gravity wave radiation from the elliptical vortex in the f -plane shallow water system

Sugimoto¹

2017

Fluid Dyn. Res.

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Inertia-gravity wave (IGW) radiation from the elliptical vortex is investigated in the f-plane shallow water system. The far field of IGW is analytically derived for the case of an almost circular Kirchhoff vortex with a small aspect ratio. Cyclone-anticyclone asymmetry appears at finite values of the Rossby number (Ro) caused by the source originating in the Coriolis acceleration. While the intensity of IGWs from the cyclone monotonically decreases as f increases, that from the anticyclone increases as f increases for relatively smaller f and has a local maximum at intermediate f. A numerical experiment is conducted on a model using a spectral method in an unbounded domain. The numerical results agree quite well with the analytical ones for elliptical vortices with small aspect ratios, implying that the derived analytical forms are useful for the verification of the numerical model. For elliptical vortices with larger aspect ratios, however, significant deviation from the analytical estimates appears. The intensity of IGWs radiated in the numerical simulation is larger than that estimated analytically. The reason is that the source of IGWs is amplified during the time evolution because the shape of the vortex changes from ideal ellipse to elongated with filaments. Nevertheless, cyclone-anticyclone asymmetry similar to the analytical estimate appears in all the range of aspect ratios, suggesting that this asymmetry is a robust feature.

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“…Spontaneous generation by balanced flows has been obtained from simulations of the propagation of IGWs from vortex dipoles. For instance, an initially balanced flow consisting of an unstable baroclinic jet was observed to break up into a street of cyclonic and anticyclonic vortices (Viúdez & Dritschel 2006;Pàllas-Sanz & Viúdez 2008). The instability of a three-dimensional (baroclinic) jet was also reported using a triply periodic non-hydrostatic numerical model (Dritschel & Viúdez 2003;Viúdez & Dritschel 2006).…”

Section: Introductionmentioning

confidence: 92%

Inertia–gravity waves in a liquid-filled, differentially heated, rotating annulus

Randriamampianina

Arco²

2015

J. Fluid Mech.

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International audienceDirect numerical simulations based on high-resolution pseudospectral methods are carried out for detailed investigation into the instabilities arising in a differentially heated, rotating annulus, the baroclinic cavity. Following previous works using air (Randriamampianina et al., J. Fluid Mech., vol. 561, 2006, pp. 359–389), a liquid defined by Prandtl number Pr=16 is considered in order to better understand, via the Prandtl number, the effects of fluid properties on the onset of gravity waves. The computations are particularly aimed at identifying and characterizing the spontaneously emitted small-scale fluctuations occurring simultaneously with the baroclinic waves. These features have been observed as soon as the baroclinic instability sets in. A three-term decomposition is introduced to isolate the fluctuation field from the large-scale baroclinic waves and the time-averaged mean flow. Even though these fluctuations are found to propagate as packets, they remain attached to the background baroclinic waves, locally triggering spatio-temporal chaos, a behaviour not observed with the air-filled cavity. The properties of these features are analysed and discussed in the context of linear theory. Based on the Richardson number criterion, the characteristics of the generation mechanism are consistent with a localized instability of the shear zonal flow, invoking resonant over-reflection

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Spontaneous Generation of Inertia–Gravity Waves during the Merging of Two Baroclinic Anticyclones

Cited by 11 publications

References 37 publications

The merger of geophysical vortices at finite Rossby and Froude number

The merger of geophysical vortices at finite Rossby and Froude number

Inertia–gravity wave radiation from the elliptical vortex in the f -plane shallow water system

Inertia–gravity waves in a liquid-filled, differentially heated, rotating annulus

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