Pi1B pulsations as a possible driver of Alfvénic aurora at substorm onset

Lessard, M.; Lund, E. J.; Kim, H. M.; Engebretson, M. J.; Hayashi, K.

doi:10.1029/2010ja015776

Cited by 21 publications

(22 citation statements)

References 36 publications

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“…Strong Alfvenic turbulence is commonly observed in the PSBL at 4–6 R E geocentric distance with the Polar spacecraft during the expansion phase of substorms [ Wygant et al ., ; Keiling et al ., ]. Lessard et al [] found a relationship between Pi1B pulsations originating from beyond geosynchronous orbit and wave‐driven aurora during the onset of a substorm, suggesting that the pulsations propagating from the magnetotail are powering the aurora. Pi1B pulsations are bursty waves with frequencies from 25 mHz to 1 Hz; sometimes higher frequencies are seen too.…”

Section: Discussionmentioning

confidence: 99%

The optical manifestation of dispersive field‐aligned bursts in auroral breakup arcs

et al. 2013

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[1] High-resolution optical observations of a substorm expansion show dynamic auroral rays with surges of luminosity traveling up the magnetic field lines. Observed in ground-based imagers, this phenomenon has been termed auroral flames, whereas the rocket signatures of the corresponding energy dispersions are more commonly known as field-aligned bursts. In this paper, observations of auroral flames obtained at 50 frames/s with a scientific-grade Complementary Metal Oxide Semiconductor (CMOS) sensor (30 ı 30 ı field of view, 30 m resolution at 120 km) are used to provide insight into the nature of the precipitating electrons similar to high-resolution particle detectors. Thanks to the large field of view and high spatial resolution of this system, it is possible to obtain a first-order estimate of the temporal evolution in altitude of the volume emission rate from a single sensor. The measured volume emission rates are compared with the sum of modeled eigenprofiles obtained for a finite set of electron beams with varying energy provided by the TRANSCAR auroral flux tube model. The energy dispersion signatures within each auroral ray can be analyzed in detail during a fraction of a second. The evolution of energy and flux of the precipitation shows precipitation spanning over a large range of energies, with the characteristic energy dropping from 2.1 keV to 0.87 keV over 0.2 s. Oscillations at 2.4 Hz in the magnetic zenith correspond to the period of the auroral flames, and the acceleration is believed to be due to Alfvenic wave interaction with electrons above the ionosphere.

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Section: Discussionmentioning

confidence: 99%

The optical manifestation of dispersive field‐aligned bursts in auroral breakup arcs

et al. 2013

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“…The mode of the discharging current is beyond the scope of this paper, but it is emphasized that as mentioned earlier, the acceleration process of the UL electrons is expected to be different from that of the DD current (Karlsson 2012). In this regard, Mende (2003) found that the field-aligned current associated with the poleward advancing arc is carried by superthermal electrons accompanied by waves, which may be related to Pi1B pulsations (Lessard et al 2011). …”

Section: Deflationmentioning

confidence: 99%

Auroral Substorms: Search for Processes Causing the Expansion Phase in Terms of the Electric Current Approach

Akasofu

2017

Space Sci Rev

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Auroral substorms are mostly manifestations of dissipative processes of electromagnetic energy. Thus, we consider a sequence of processes consisting of the power supply (dynamo), transmission (currents/circuits) and dissipations (auroral substorms-the end product), namely the electric current line approach. This work confirms quantitatively that after accumulating magnetic energy during the growth phase, the magnetosphere unloads the stored magnetic energy impulsively in order to stabilize itself. This work is based on our result that substorms are caused by two current systems, the directly driven (DD) current system and the unloading system (UL). The most crucial finding in this work is the identification of the UL (unloading) current system which is responsible for the expansion phase. A very tentative sequence of the processes leading to the expansion phase (the generation of the UL current system) is suggested for future discussions.(1) The solar wind-magnetosphere dynamo enhances significantly the plasma sheet current when its power is increased above 10 18 erg/s (10 11 w). (2) The magnetosphere accumulates magnetic energy during the growth phase, because the ionosphere cannot dissipate the increasing power because of a low conductivity. As a result, the magnetosphere is inflated, accumulating magnetic energy. (3) When the power reaches 3-5 × 10 18 erg/s (3-5 × 10 11 w) for about one hour and the stored magnetic energy reaches 3-5 × 10 22 ergs (10 15 J), the magnetosphere begins to develop perturbations caused by current instabilities (the current density ≈3 × 10 −12 A/cm 2 and the total current ≈10 6 A at 6 Re). As a result, the plasma sheet current is reduced. (4) The magnetosphere is thus deflated. The current reduction causes ∂B/∂t > 0 in the main body of the magnetosphere, producing an earthward electric field. As it is transmitted to the ionosphere, it becomes equatorward-directed electric field which drives both Pedersen and Hall currents and thus generates the UL current system. (6) The substorm intensity depends on the location of the energy accumulation (between 4 Re and 10 Re), the closer the location to the earth, the more intense substorms becomes, because the capacity of holding the energy is higher at closer distances. The convective flow toward the earth brings both the ring current and the plasma sheet current closer when the dynamo power becomes higher.This proposed sequence is not necessarily new. Individual processes involved have been considered by many, but the electric current approach can bring them together systematically and provide some new quantitative insights.

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“…KAWs have been found in the plasma sheet associated with fast flows (Angelopoulos et al, 2002;Chaston et al, 2009Chaston et al, , 2012, at the plasma sheet boundary layer (PSBL; Gershman et al, 2017;Wygant et al, 2002), and in the inner magnetosphere (Chaston et al, 2006(Chaston et al, , 2014Huang et al, 1997). It has been argued that Journal of Geophysical Research: Space Physics 10.1029/2019JA027062 the KAWs observed around the tail plasma sheet carry sufficient Poynting flux flowing along magnetic field lines toward the ionosphere to power low-altitude auroral acceleration (Angelopoulos et al, 2002;Lessard et al, 2011).…”

Section: Introductionmentioning

confidence: 99%

Kinetic Alfvén Waves From Magnetotail to the Ionosphere in Global Hybrid Simulation Associated With Fast Flows

et al. 2020

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We have used the Auburn Global Hybrid Code in 3‐D to study the generation, dynamics, and global structure of kinetic Alfvén waves (KAWs) from the magnetotail to the ionosphere. Our results show that KAWs are generated in magnetic reconnection in the plasma sheet, located around fast flows, and carrying transverse electromagnetic perturbations, parallel Poynting fluxes, parallel currents, and parallel electric field. Overall, shear Alfvénic turbulent spectrum is found in the plasma sheet. The KAWs are shear Alfvén waves possessing short perpendicular wavelength with k⊥ρi∼1, where k⊥ is the perpendicular wave number and ρi the ion Larmor radius. The KAWs are identified by their dispersion relation and polarizations. The structures of these KAWs embedded in the plasma sheet are also revealed by placing a virtual satellite in the tail. In order to understand whether the Poynting fluxes carried by the shear Alfvén waves/KAWs in the plasma sheet can be carried directly along field lines to the ionosphere, we have tracked the wave propagation from the plasma sheet to the ionosphere. It is found that in front of the flow‐braking region, the structure and strength of the shear Alfvén waves are significantly altered due to interaction with the dipole‐like field, mainly by the flow shear associated with the azimuthal convection. Also in front of the dipole‐like field region, ion kinetic effects (Hall effects) lead to the generation of additional pairs of KAWs. As such, the generation and transport of the shear Alfvén waves/KAWs to the ionosphere are illustrated for the first time in a comprehensive manner on the global scale.

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Pi1B pulsations as a possible driver of Alfvénic aurora at substorm onset

Cited by 21 publications

References 36 publications

The optical manifestation of dispersive field‐aligned bursts in auroral breakup arcs

The optical manifestation of dispersive field‐aligned bursts in auroral breakup arcs

Auroral Substorms: Search for Processes Causing the Expansion Phase in Terms of the Electric Current Approach

Kinetic Alfvén Waves From Magnetotail to the Ionosphere in Global Hybrid Simulation Associated With Fast Flows

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