Small-Scale Dynamic Aurora

Kataoka, Ryuho; Chaston, C. C.; Knudsen, D. J.; Lynch, K. A.; Lysak, R. L.; Song, Yan; Rankin, R.; Murase, Kiyoka; Sakanoi, Takeshi; Semeter, J. L.; Watanabe, Toshiya; Whiter, Daniel

doi:10.1007/s11214-021-00796-w

Cited by 14 publications

(14 citation statements)

References 218 publications

(259 reference statements)

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“…The connection of kinetic Alfvén waves with the aurora at Earth has been well established with observations from the FAST satellite (e.g., Chaston et al 2007 ) and, more recently, from the Swarm constellation of satellites (Wu et al 2020 ). A recent review of dynamic aurora phenomena has also been given by Kataoka et al ( 2021 ), while the quasi-static acceleration at Earth generally produces more energetic electrons and larger energy fluxes, as we have seen above these can also be Alfvénic in character, due to the low frequencies of field line resonances.…”

Section: Discussionsupporting

confidence: 60%

Kinetic Alfvén waves and auroral particle acceleration: a review

Lysak

2023

Rev. Mod. Plasma Phys.

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Shear mode Alfvén waves are the carriers of field-aligned currents in the auroral zones of Earth and other planets. These waves travel along the magnetic field lines, coupling the outer magnetosphere with the ionosphere. However, in ideal magnetohydrodynamic (MHD) theory, the shear mode Alfvén wave does not carry a parallel electric field that could accelerate auroral particles. This can be modified by including kinetic effects, which lead to a parallel electric field when the perpendicular wavelength becomes comparable to the electron inertial length or the ion acoustic gyroradius. These small perpendicular wavelengths can be formed by phase mixing, ionospheric feedback, or nonlinear effects. Kinetic Alfvén waves are further constrained by their interaction with the ionosphere, which acts as a reflector for these waves. In addition, the strong plasma gradients in the topside ionosphere form an effective resonator that leads to fluctuations on time scales of seconds. These rapidly changing parallel electric fields can lead to broadband acceleration of auroral electrons, often called the Alfvénic aurora. Such interactions do not only take place in Earth’s magnetosphere, but have also been observed in Jupiter’s magnetosphere by the Juno satellite.

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Section: Discussionsupporting

confidence: 60%

Kinetic Alfvén waves and auroral particle acceleration: a review

Lysak

2023

Rev. Mod. Plasma Phys.

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“…Such thin arcs often behave more dynamically (i.e., not quasistatic), some of which is closely related to time-varying magnetic field-aligned electric fields associated with dispersive Alfvén waves [501], [502], [503], [504]. Details of the smallscale dynamic discrete aurora can be found in the review of Kataoka et al [505]. The above-mentioned types of the discrete aurora (quasi-static arc and small-scale dynamic arc) are mainly observed within the main auroral oval (see [506,Fig.…”

Section: A Discrete Aurorasmentioning

confidence: 99%

Space Plasma Physics: A Review

Hajra

Zank

Sterken³

et al. 2023

IEEE Trans. Plasma Sci.

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“…Such gradients would be more common than we think, according to Partamies et al (2010). A review of the topic is provided in Kataoka et al (2021). Knudsen et al (2001) did find a lower auroral scale size boundary of 8 km with a 1.7 km pixel resolution, which was later determined by Partamies et al (2010) to be an instrumental effect.…”

Section: Coherent Scatter With a Doppler Shift Of ≥450 M/smentioning

confidence: 88%

The Properties of ICEBEAR E‐Region Coherent Radar Echoes in the Presence of Near Infrared Auroral Emissions, as Measured by the Swarm‐E Fast Auroral Imager

et al. 2021

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For the first time, near infrared (NIR) auroral emissions measured from space have been compared with E‐region coherent scatter. The E‐region coherent scatter observations were obtained by the 49.5 MHz Ionospheric Continuous‐wave E‐region Bistatic Experimental Auroral Radar (ICEBEAR) in western Canada. NIR emissions integrated over 650–1,100 nm wavelengths were obtained from the Fast Auroral Imager instrument onboard e‐POP on CASSIOPE (now Swarm‐E) with a 1 s temporal resolution (same as ICEBEAR), with the instrument slewed to the center of the ICEBEAR field‐of‐view. The coherent echoes and the NIR emissions are expected to originate below 120 km altitude. The radar spectra indicated that the turbulence was very weak. The location of all coherent echoes corresponded to NIR emission brightness values of more than 250 kR (kilo‐Rayleighs) and less than 1,250 kR. When the emissions were very bright, the electric fields were seemingly too weak to produce plasma instabilities, explaining why no radar echoes were detected. By contrast, even if the electric field happened to be relatively strong in dark regions, the background plasma densities were too small to generate detectable coherent scatter radar echoes. The Doppler shifts of the coherent scatter spectra were clustered around 465 and ± 250 m/s. These magnitudes did not agree with the quiet 350 m/s ion‐acoustic speed expected from the weaker electric fields that should have prevailed under weak turbulence situations. The unexpected Doppler shifts were potentially due to either unexpected strong electric fields and altitude variations, or ambient km‐size density gradients at 110 km.

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Small-Scale Dynamic Aurora

Cited by 14 publications

References 218 publications

Kinetic Alfvén waves and auroral particle acceleration: a review

Kinetic Alfvén waves and auroral particle acceleration: a review

Space Plasma Physics: A Review

The Properties of ICEBEAR E‐Region Coherent Radar Echoes in the Presence of Near Infrared Auroral Emissions, as Measured by the Swarm‐E Fast Auroral Imager

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