Impulsive enhancements of oxygen ions during substorms

Fok, M.‐C.; Moore, T. E.; Brandt, P. C.; Delcourt, Dominique; Slinker, S. P.; Fedder, J. A.

doi:10.1029/2006ja011839

Cited by 108 publications

(152 citation statements)

References 52 publications

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“…Figure 38(a) shows an example (Frank 1970). A simulation study of an imaged ring current shows also that the ring current belt was located between 3 and 7 L during a moderate storm (Fok et al 2006). Thus, there is an indication that the substorm intensity depends on the location of the accumulated energy, as well as the power ε.…”

Section: Storm Intensity and The Location Of The Energy Accumulationmentioning

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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Section: Storm Intensity and The Location Of The Energy Accumulationmentioning

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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“…It has been suggested that the ionospheric origin of low-energy O + ions in the lobe/plasma sheet are strongly accelerated at the magnetic reconnection region (X = −20 to −30 R E ), and are subsequently transported into the nearEarth plasma sheet Wilken et al, 1995;Zong et al, 1997Zong et al, , 1998]. Also proposed is that the energization of O + ions is caused by substorm-associated magnetic field reconfiguration and/or current sheet acceleration [Delcourt et al, 1990;Sánchez et al, 1993;Nosé et al, 2000;Fok et al, 2006;Nosé et al, 2009]. However, it was argued by Daglis and Axford [1996] that there existed a direct short-timescale feeding of the magnetosphere with ionospheric ions, indicating the injection of O + ions to the ring current region was faster than the traditional concepts as described in the paper by Kamide et al [1998].…”

Section: Introductionmentioning

confidence: 99%

The role of ULF waves interacting with oxygen ions at the outer ring current during storm times

Yang

Zong

et al. 2011

J. Geophys. Res.

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[1] The modulations of the outer ring current O + ion fluxes by ULF Pc5 waves are investigated by multisatellite observations during storm times. The O + ions have energies up to tens of keV. We concentrate on the process in terms of drift-bounce resonance of O + ions with ULF standing waves to understand whether the ring current O + ions could be accelerated/decelerated by ULF waves. Two case studies are performed, in which the Cluster satellites travel the outer ring current region in the morning sector with radial distances of about 5.5 R E . Distinct O + ion flux oscillations are observed associated with fundamental mode ULF standing waves. On 25 October 2002, both satellites SC1 and SC4 observe strong poloidal and toroidal standing waves at approximately the same region one by one with a time lag of 45 min. The O + ion flux oscillations at around 20 keV are dominantly coherent with the poloidal standing wave at 3.4 mHz with cross phases of near 90°with respect to the magnetic field waves. The O + phase space density spectra at 10 to 25 keV, measured by both satellites, deviate significantly from the typical power law distribution. We suggest that the O + ions at 10 to 25 keV are accelerated due to drift-bounce resonance with the poloidal standing wave. On 4 November 2002, satellite SC1 observes considerable poloidal and toroidal standing waves. The O + ion flux oscillation at around 7 keV is well correlated with both of the two wave modes at 3.7 mHz with cross phases of about 90°with respect to the magnetic field waves. The O + spectra at 4 to 8 keV deviates remarkably from the background power law distribution. When satellite SC4 closely encounters the same region 40 min later, the wave activities at 3.7 mHz are found to be rather weak and the O + spectra is close to the background power law distribution. We suggest that the spectra variation of SC1 results from the deceleration of O + ion at 4 to 8 keV via drift-bounce resonances during the strong wave activities. The observations made in this study reveal the effective role of ULF standing waves in accelerating/decelerating the ring current O + ions.Citation: Yang, B., Q.-G. Zong, S. Y. Fu, X. Li, A. Korth, H. S. Fu, C. Yue, and H. Reme (2011), The role of ULF waves interacting with oxygen ions at the outer ring current during storm times,

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“…Ionospheric plasma is highly collisional, and the plasma above ∼500 km is essentially collisionless. It has been recently realized that for a successful description of such a plasma system, a complex solution is needed which allows different physics domains to be described using different physical models (De Zeeuw et al, 2004;Fok et al, 2006;Moore et al, 2008;Ridley et al, 2004;Tóth et al, 2005;Tóth et al, 2011;Zhang, Liemohn, De Zeeuw, Borovsky, Ridley, Toth, Sazykin, Thomsen, Kozyra, Gombosi & Wolf, 2007). This is the reason why coupled models are intensively developed and improved during recent years.…”

Section: Discussion and Directions For Future Workmentioning

confidence: 99%

Impact of Solar Wind on the Earth Magnetosphere: Recent Progress in the Modeling of Ring Current and Radiation Belts

Buzulukova¹,

Fok²,

Glocer³

2012

Exploring the Solar Wind

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Impulsive enhancements of oxygen ions during substorms

Cited by 108 publications

References 52 publications

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

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

The role of ULF waves interacting with oxygen ions at the outer ring current during storm times

Impact of Solar Wind on the Earth Magnetosphere: Recent Progress in the Modeling of Ring Current and Radiation Belts

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