Buoyancy Waves in Earth's Magnetosphere: Calculations for a 2‐D Wedge Magnetosphere

Wolf, R. A.; Toffoletto, F.; Schutza, A. M.; Yang, Jian

doi:10.1029/2017ja025006

Cited by 11 publications

(49 citation statements)

References 26 publications

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“… 2014 ). If stopping flow bursts overshoot their equilibrium position, they may start performing interchange (or buoyancy) oscillations around that position (Wolf et al 2012 , 2018 ; Panov et al. 2013b ).…”

Section: Explosive Magnetotail Dynamicsmentioning

confidence: 99%

Explosive Magnetotail Activity

et al. 2019

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Modes and manifestations of the explosive activity in the Earth’s magnetotail, as well as its onset mechanisms and key pre-onset conditions are reviewed. Two mechanisms for the generation of the pre-onset current sheet are discussed, namely magnetic flux addition to the tail lobes, or other high-latitude perturbations, and magnetic flux evacuation from the near-Earth tail associated with dayside reconnection. Reconnection onset may require stretching and thinning of the sheet down to electron scales. It may also start in thicker sheets in regions with a tailward gradient of the equatorial magnetic field ; in this case it begins as an ideal-MHD instability followed by the generation of bursty bulk flows and dipolarization fronts. Indeed, remote sensing and global MHD modeling show the formation of tail regions with increased , prone to magnetic reconnection, ballooning/interchange and flapping instabilities. While interchange instability may also develop in such thicker sheets, it may grow more slowly compared to tearing and cause secondary reconnection locally in the dawn-dusk direction. Post-onset transients include bursty flows and dipolarization fronts, micro-instabilities of lower-hybrid-drift and whistler waves, as well as damped global flux tube oscillations in the near-Earth region. They convert the stretched tail magnetic field energy into bulk plasma acceleration and collisionless heating, excitation of a broad spectrum of plasma waves, and collisional dissipation in the ionosphere. Collisionless heating involves ion reflection from fronts, Fermi, betatron as well as other, non-adiabatic, mechanisms. Ionospheric manifestations of some of these magnetotail phenomena are discussed. Explosive plasma phenomena observed in the laboratory, the solar corona and solar wind are also discussed.

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Section: Explosive Magnetotail Dynamicsmentioning

confidence: 99%

Explosive Magnetotail Activity

et al. 2019

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“…That is probably due to the fact that the rapidly earthward moving bubble, which is a highly nonlinear disturbance, generates waves in a Cherenkov pattern, creating a V pointed in the direction of motion (earthward). The dispersion relation for short‐wavelength buoyancy waves (Wolf et al, ) is

ω = \frac{ω_{b}}{\sqrt{1 + \frac{k_{r}^{2}}{k_{y}^{2}}}}

where ω b is the buoyancy frequency. Combined with the Cherenkov condition

ω = - k_{r} v_{o}

, equation gives the following expression for the Cherenkov opening angle:

\tan θ_{C} = \frac{k_{y}}{k_{r}} = {[\frac{2}{- 1 + \sqrt{1 + 4 {(\frac{ω_{b}}{ω})}^{2}}}]}^{1 / 2} \approx \pm \frac{k_{y} v_{o}}{ω_{b}}

…”

Section: Comparison With Mhd Modelsmentioning

confidence: 99%

The Inertialized Rice Convection Model

et al. 2019

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The Rice Convection Model (RCM) is an established first‐principles physics model in which the field‐aligned current density is computed by the Vasyliunas equation. Its slow‐flow assumption neglects the inertial term in the MHD momentum equation, which is a major obstacle to using the RCM to model some of the fluid dynamics of bursty bulk flows in the plasma sheet. This paper describes the RCM‐I, which represents an effort to approximately add inertial effects in the RCM by correcting the expression for field‐aligned currents. That inertial current is calculated under the assumption that the mass on each field line is concentrated near the equatorial plane. RCM‐I results are presented with magnetic fields calculated in two different ways: A static statistics‐based model and an MHD code. In both cases, the bubble flow velocities are much smaller and more realistic than those calculated from the traditional RCM. An additional promising feature is that the injection of a low‐entropy bubble produces interchange (braking) oscillations and buoyancy waves that radiate away from the original bubble, forming multiple flow vortices. None of these features could be produced by traditional RCM simulations. Comparison simulations also suggest that gradient and curvature drifts have substantial effect on oscillation of bubbles and tend to damp buoyancy waves. We also note that substantial work will be needed in the future to further improve the pressure distribution by inertializing an anisotropic version of the RCM and to understand the effects of neglecting the magnetosphere‐ionosphere communication time.

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“…Indeed, in this form, it is easy to see that dropping velocity shear terms yields precisely the equation in Wolf et al ():

\begin{matrix} right ω^{2} δ v_{r} & left = \frac{ω}{ρ_{0}} \frac{d}{d r} (- \frac{δ v_{r} ρ_{0} ω (c_{s}^{2} - c_{A}^{2})}{r (ω^{2} - k_{y}^{2} c_{f}^{2})} - \frac{d δ v_{r}}{d r} \frac{c_{f}^{2} ρ_{0} ω}{ω^{2} - k_{y}^{2} c_{f}^{2}}) & right \\ right & left + \frac{2 c_{A}^{2}}{r} (\frac{δ v_{r}}{Γ c_{f}^{2}} [c_{s}^{2} \frac{K_{0}^{'}}{K_{0}} - \frac{ω^{2} Γ (c_{s}^{2} - c_{A}^{2})}{r (ω^{2} - k_{y}^{2} c_{f}^{2})}] - \frac{d δ v_{r}}{d r} \frac{ω^{2}}{ω^{2} - k_{y}^{2} c_{}}) \end{matrix}

…”

Section: Magnetospheric Wave Equation For Plasma Wedgementioning

confidence: 75%

Shear Flow‐Interchange Instability in Nightside Magnetotail as Proposed Cause of Auroral Beads as a Signature of Substorm Onset

2020

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A geometric wedge model of the near-Earth nightside plasma sheet is used to derive a wave equation for low-frequency shear flow-interchange waves which transmit ⃗ E × ⃗ B sheared zonal flows along magnetic flux tubes toward the ionosphere. Discrepancies with the wave equation result used in Kalmoni et al. (2015, https://doi.org/10.1002/2015JA021470) for shear flow-ballooning instability are discussed. The shear flow-interchange instability appears to be responsible for substorm onset. The wedge wave equation is used to compute rough expressions for dispersion relations and local growth rates in the midnight region of the nightside magnetotail where the instability develops, forming the auroral beads characteristic of geomagnetic substorm onset. Stability analysis for the shear flow-interchange modes demonstrates that nonlinear analysis is necessary for quantitatively accurate results and determines the spatial scale on which the instability varies.

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Buoyancy Waves in Earth's Magnetosphere: Calculations for a 2‐D Wedge Magnetosphere

Cited by 11 publications

References 26 publications

Explosive Magnetotail Activity

Explosive Magnetotail Activity

The Inertialized Rice Convection Model

Shear Flow‐Interchange Instability in Nightside Magnetotail as Proposed Cause of Auroral Beads as a Signature of Substorm Onset

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