Pressure‐driven and ionosphere‐driven modes of magnetospheric interchange instability

Miura, Akira

doi:10.1029/2008ja013663

Cited by 13 publications

(18 citation statements)

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“…A critical factor that may affect this assumption is the ionospheric boundary condition since the interchange mode necessarily involves nonzero displacement along the ionospheric boundaries. Although a rigorous treatment of this issue is required for a precise answer (see Miura [2009] for theoretical aspect), we give some intuitive argument below.…”

Section: Discussionmentioning

confidence: 99%

Observational test of interchange instability associated with magnetic dipolarization in the near‐Earth plasma sheet ofr < 12 R_E

et al. 2012

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Interchange instability is basically a pressure gradient‐driven mode, and therefore, it may naturally be expected to be triggered in the near‐Earth tail during the growth phase of magnetic dipolarization as the tail field lines become more stretched by an increasing radial pressure gradient. To examine this possibility, we have tested the classic interchange criterion by using the plasma and magnetic field observations from the THEMIS inner tail probes atr < 12 RE. Both the specific events and the statistical results of this study indicate that the stretched tail field configurations during the dipolarization growth phase are actually stable to the interchange mode. Considering that the interchange mode is formally regarded as a special case of the more general ballooning mode, our conclusion of the interchange mode stability prior to the dipolarization onset eliminates one family of the pressure gradient‐driven modes as a possible trigger of dipolarization at the near‐Earth tail. However, interestingly, we find the possibility that sometimes, the near‐tail field configurations can become less stable and even occasionally be unstable after they become rounder through the dipolarization process, although this possibility requires more rigorous test for a solid conclusion.

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Section: Discussionmentioning

confidence: 99%

Observational test of interchange instability associated with magnetic dipolarization in the near‐Earth plasma sheet ofr < 12 R_E

et al. 2012

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“…From equation through equation in Miura [], terms arising from k ⟂ I , which is the wave number vector at the ionosphere, were mistakenly calculated by using k ⟂ e q , which is the wave number vector in the equatorial plane. Thus, from equation through equation , those terms should be multiplied by α , which is defined by

α = \frac{k_{⟂ I}^{2}}{k_{⟂ eq}^{2}} .

Equations (C1)–(C5), which are necessary for the calculation of the explicit form of

{boldk}_{⟂}^{2}

at arbitrary r and θ in the spherical coordinates ( r , θ , φ ), were newly added after equation (105) as shown below.…”

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confidence: 99%

“…In other words,

{boldk}_{⟂ I}^{2} > {boldk}_{⟂ eq}^{2}

for L >1 owing to the geometrical constriction of a magnetic flux tube toward the ionosphere. Thus, the ionospheric destabilizing contribution δ W I to the potential energy variation δ W was underestimated in Miura [], because | δ W I | is proportional to

{boldk}_{⟂ I}^{2}

. Therefore, the following corrections due to the introduction of the correction factor α do not cause any essential change in one of the conclusions of the paper, which indicates that a substantial region of the inner magnetosphere with the equatorial plasma β less than one may be unstable against the ionosphere‐driven interchange instability, which is caused by a horizontal plasma displacement on the spherical ionospheric surface.…”

mentioning

confidence: 99%

“…Necessary modifications to Miura [], which are caused by the introduction of the correction factor α , are as follows: In paragraph [1] (abstract) of Miura [], the second and last sentences from the bottom

“For an axisymmetric, north‐south symmetric and low‐ β magnetospheric model, in which the magnetic field is approximated by a dipole field, the m =1 or m =2 ionosphere‐driven mode, where m is the azimuthal mode number, has an upper critical equatorial β value for instability in the order of one. Thus a substantial region of the inner magnetosphere or the near‐earth magnetosphere may be unstable against ionosphere‐driven interchange instability caused by a horizontal plasma displacement on the spherical ionospheric surface.”should read

“For an axisymmetric, north‐south symmetric and low‐ β magnetospheric model, in which the magnetic field is approximated by a dipole field, ionosphere‐driven interchange modes with m = 1∼34, where m is the azimuthal mode number, have upper critical equatorial β values for instability exceeding the order of one.…”

mentioning

confidence: 99%

“…In paragraph [1] (abstract) of Miura [], the second and last sentences from the bottom

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Correction to “Pressure‐driven and ionosphere‐driven modes of magnetospheric interchange instability”

Miura

2013

JGR Space Physics

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[1] In the paper "Pressure-driven and ionosphere-driven modes of magnetospheric interchange instability" by A. Miura (Journal of Geophysical Research, 114, A02224, doi:10.1029/2008JA013663, 2009, there were substantial errors in the equations. These errors were made by the mistaken use of the wave number vector in the equatorial plane instead of the wave number vector at the ionosphere in evaluating an ionospheric destabilizing contribution to the potential energy variation. Owing to these errors, the ionospheric destabilizing contribution to the potential energy variation was underestimated. This Correction provides the accurate form of the potential energy variation and corrects a quantitative prediction in the paper about the range of the azimuthal mode number m of unstable ionosphere-driven interchange modes in an axisymmetric inner magnetospheric model with a dipole magnetic field.[2] From equation (106) through equation (120) in Miura [2009], terms arising from k ?I , which is the wave number vector at the ionosphere, were mistakenly calculated by using k ?eq , which is the wave number vector in the equatorial plane. Thus, from equation (106) through equation (120), those terms should be multiplied by˛, which is defined by˛=Equations (C1)-(C5), which are necessary for the calculation of the explicit form of k 2 ? at arbitrary r and Â in the spherical coordinates (r, Â , ), were newly added after equation (105) as shown below. One can calculate the correction factor˛by using equation (C4) asIt is obvious that˛ 1 and˛= 1 occurs at L = 1.©2013. American Geophysical Union. All Rights Reserved. 2169-9380/13/10.1002/jgra.50173In other words, k?eq for L > 1 owing to the geometrical constriction of a magnetic flux tube toward the ionosphere. Thus, the ionospheric destabilizing contribution ıW I to the potential energy variation ıW was underestimated in Miura [2009], because |ıW I | is proportional to k 2 ?I . Therefore, the following corrections due to the introduction of the correction factor˛do not cause any essential change in one of the conclusions of the paper, which indicates that a substantial region of the inner magnetosphere with the equatorial plasmaˇless than one may be unstable against the ionosphere-driven interchange instability, which is caused by a horizontal plasma displacement on the spherical ionospheric surface. As shown below, one will find by the following corrections that ionosphere-driven interchange modes with a wider range of the azimuthal mode number m than m . 2 predicted by mistakenly using k ?eq instead of k ?I become unstable in the inner magnetosphere.[3] Necessary modifications to Miura [2009], which are caused by the introduction of the correction factor˛, are as follows:[4] 1. In paragraph [1] (abstract) of Miura [2009], the second and last sentences from the bottom "For an axisymmetric, north-south symmetric and lowmagnetospheric model, in which the magnetic field is approximated by a dipole field, the m = 1 or m = 2 ionosphere-driven mode, where m is the azimuthal mode number,...

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Auroral fragmentation into patches

et al. 2014

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Auroral patches in diffuse auroras are very common features in the postmidnight local time.However, the processes that produce auroral patches are not yet well understood. In this paper we present two examples of auroral fragmentation which is the process by which uniform aurora is broken into several fragments to form auroral patches. These examples were observed at Athabasca, Canada (geomagnetic latitude: 61.7 • N), and Tromsø, Norway (67.1 • N). Captured in sequences of images, the auroral fragmentation occurs as finger-like structures developing latitudinally with horizontal-scale sizes of 40-100 km at ionospheric altitudes. The structures tend to develop in a north-south direction with speeds of 150-420 m/s without any shearing motion, suggesting that pressure-driven instability in the balance between the earthward magnetic-tension force and the tailward pressure gradient force in the magnetosphere is the main driving force of the auroral fragmentation. Therefore, these observations indicate that auroral fragmentation associated with pressure-driven instability is a process that creates auroral patches. The observed slow eastward drift of aurora during the auroral fragmentation suggests that fragmentation occurs in low-energy ambient plasma.

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Pressure‐driven and ionosphere‐driven modes of magnetospheric interchange instability

Cited by 13 publications

References 24 publications

Observational test of interchange instability associated with magnetic dipolarization in the near‐Earth plasma sheet ofr < 12 R_E

Observational test of interchange instability associated with magnetic dipolarization in the near‐Earth plasma sheet ofr < 12 R_E

Correction to “Pressure‐driven and ionosphere‐driven modes of magnetospheric interchange instability”

Auroral fragmentation into patches

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Pressure‐driven and ionosphere‐driven modes of magnetospheric interchange instability

Cited by 13 publications

References 24 publications

Observational test of interchange instability associated with magnetic dipolarization in the near‐Earth plasma sheet ofr < 12 RE

Observational test of interchange instability associated with magnetic dipolarization in the near‐Earth plasma sheet ofr < 12 RE

Correction to “Pressure‐driven and ionosphere‐driven modes of magnetospheric interchange instability”

Auroral fragmentation into patches

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Observational test of interchange instability associated with magnetic dipolarization in the near‐Earth plasma sheet ofr < 12 R_E

Observational test of interchange instability associated with magnetic dipolarization in the near‐Earth plasma sheet ofr < 12 R_E