Parameter Sweep Experiments on Spontaneous Gravity Wave Radiation from Unsteady Rotational Flow in an f-Plane Shallow Water System

Sugimoto, Norihiko; Ishioka, Keiichi; Ishii, Katsuya

doi:10.1175/2007jas2404.1

Cited by 19 publications

(31 citation statements)

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“…5 While gravity wave radiation in a shallow water system is different from that in a continuously stratified one, 6 their fundamental study in geophysical fluid dynamics is nevertheless important. 3 Spontaneous gravity wave radiation from unsteady vortical flows in rotating shallow water has been investigated 5,[7][8][9] and cyclone-anticyclone asymmetry has recently been found. 10 However, it is not evident whether this asymmetry appears in complicated vortical flows, since analysis and numerical verification were performed only for an idealized case of a co-rotating point vortex pair.…”

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confidence: 99%

“…8,10 In Ref. 10, the intensity of the gravity waves from a co-rotating point vortex pair with a constant rotation rate Ω is analytically derived, which is estimated using the following equation:…”

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confidence: 99%

“…10. Spontaneous gravity wave radiation in rotating shallow water is analogous to sound emission from a vortex (Lighthill-Ford theory 6,18 ); the quadrupole source of waves is approximately expressed using the unsteady motions of vortical flows, In addition, the source originating in Coriolis acceleration is important at smaller Ro, [8][9][10] which is expressed as…”

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Inertia-gravity wave radiation from the merging of two co-rotating vortices in the f-plane shallow water system

Sugimoto

2015

Physics of Fluids

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Inertia-gravity wave radiation from the merging of two co-rotating vortices is investigated numerically in a rotating shallow water system in order to focus on cyclone–anticyclone asymmetry at different values of the Rossby number (Ro). A numerical study is conducted on a model using a spectral method in an unbounded domain to estimate the gravity wave flux with high accuracy. Continuous gravity wave radiation is observed in three stages of vortical flows: co-rotating of the vortices, merging of the vortices, and unsteady motion of the merged vortex. A cyclone–anticyclone asymmetry appears at all stages at smaller Ro (≤20). Gravity waves from anticyclones are always larger than those from cyclones and have a local maximum at smaller Ro (∼2) compared with that for an idealized case of a co-rotating vortex pair with a constant rotation rate. The source originating in the Coriolis acceleration has a key role in cyclone–anticyclone asymmetry in gravity waves. An additional important factor is that at later stages, the merged axisymmetric anticyclone rotates faster than the elliptical cyclone due to the effect of the Rossby deformation radius, since a rotation rate higher than the inertial cutoff frequency is required to radiate gravity waves.

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Inertia-gravity wave radiation from the merging of two co-rotating vortices in the f-plane shallow water system

Sugimoto

2015

Physics of Fluids

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“…In this study, we extend the previous f -plane study (Sugimoto et al 2008) onto a sphere. In the previous study, we investigated gravity wave radiation from an unsteady jet in a wide parameter range as an extension of the Ford theory (Ford 1994).…”

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confidence: 70%

“…The other way is to use simpler configuration models of an f -plane shallow water system (Ford 1994;Sugimoto et al 2005Sugimoto et al , 2007bSugimoto et al , 2008. This is the simplest system in which both rotational flows and inertial gravity waves exist.…”

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confidence: 99%

Spontaneous Gravity Wave Radiation in a Shallow Water System on a Rotating Sphere

Sugimoto

Ishii

2012

Journal of the Meteorological Society of Japan

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The effect of the earth's rotation on spontaneous inertial gravity wave radiation from an unsteady rotational flow is investigated numerically using a shallow water system on a rotating sphere, changing three parameters, the Rossby number (1 ≤ Ro ≤ 30), the Froude number (0.1 ≤ Fr ≤ 0.7), and the latitudinal positions of the jet (11.25 • N ≤ θ 0 ≤ 78.75 • N). The spectral-like three-point combined compact difference (sp-CCD) scheme is used for numerical calculation to estimate the amplitude of gravity waves with high accuracy and resolution similar to the spherical harmonics model. The jet, which is initially balanced but evolves with time because of barotropic instability, is maintained by relaxation forcing. The time variations of nearly balanced rotational flows continuously radiate gravity waves. While the amount of gravity wave flux for large Ro (≥ 10) in all positions of the jet is almost constant, that for relatively small Ro (< 10) depends considerably on the positions of the jet and the observational latitude. First, there is almost no gravity wave radiation from the jet positioned at a high latitude. Second, even when gravity waves are radiated from the jet positioned at low latitude, they rarely propagate toward a higher latitude. To discuss the results, the source of gravity waves is introduced as an analogy to the aeroacoustic sound wave radiation theory (Lighthill theory) with an f -plane approximation at the position of the jet. Spectral analysis of the sources reasonably explains the waves. Because the effect of the earth's rotation varies with the latitude, gravity waves are radiated only from an unsteady source with higher frequency than the inertial cut-off frequency at the position of the jet. In a similar way, gravity waves that propagate toward high latitudes should have a higher frequency than the inertial cut-off frequency at that latitude.

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Internal gravity waves from atmospheric jets and fronts

2014

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For several decades, jets and fronts have been known from observations to be significant sources of internal gravity waves in the atmosphere. Motivations to investigate these waves have included their impact on tropospheric convection, their contribution to local mixing and turbulence in the upper troposphere, their vertical propagation into the middle atmosphere, and the forcing of its global circulation. While many different studies have consistently highlighted jet exit regions as a favored locus for intense gravity waves, the mechanisms responsible for their emission had long remained elusive: one reason is the complexity of the environment in which the waves appear; another reason is that the waves constitute small deviations from the balanced dynamics of the flow generating them; i.e., they arise beyond our fundamental understanding of jets and fronts based on approximations that filter out gravity waves. Over the past two decades, the pressing need for improving parameterizations of nonorographic gravity waves in climate models that include a stratosphere has stimulated renewed investigations. The purpose of this review is to present current knowledge and understanding on gravity waves near jets and fronts from observations, theory, and modeling, and to discuss challenges for progress in coming years.

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Parameter Sweep Experiments on Spontaneous Gravity Wave Radiation from Unsteady Rotational Flow in an f-Plane Shallow Water System

Cited by 19 publications

References 31 publications

Inertia-gravity wave radiation from the merging of two co-rotating vortices in the f-plane shallow water system

Inertia-gravity wave radiation from the merging of two co-rotating vortices in the f-plane shallow water system

Spontaneous Gravity Wave Radiation in a Shallow Water System on a Rotating Sphere

Internal gravity waves from atmospheric jets and fronts

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