Relation of auroral substorm onset to local AL index and dispersionless particle injections

Weygand, J. M.; McPherron, R. L.; Kauristie, Kirsti; Frey, H. U.; Hsu, T.

doi:10.1016/j.jastp.2008.09.030

Cited by 14 publications

(11 citation statements)

References 33 publications

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“…The enhanced plasma density is injected from the magnetotail toward the Earth by the large electric field induced from the rapidly varying magnetic field. The above injections resemble the real substorm activities, since the AE ( AL ) index begins to sharply increase (decrease) at 09:30, 11:00, 13:30, and 16:00 UT (Figure ), approximately aligned with the modeled dipolarizations and injections, and these sharp changes in the AE / AL index occur almost simultaneously with substorm onset [ Weygand et al , ]. The large increase (decrease) in AE ( AL ) index between 18:00 and 20:00 UT suggests further substorm injections, which are however missed in the model.…”

Section: Resultsmentioning

confidence: 72%

The role of ring current particle injections: Global simulations and Van Allen Probes observations during 17 March 2013 storm

Jordanova

Welling

et al. 2014

Geophysical Research Letters

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We simulate substorm injections observed by the Van Allen Probes during the 17 March 2013 storm using a self‐consistent coupling between the ring current model RAM‐SCB and the global MHD model BATS‐R‐US. This is a significant advancement compared to previous studies that used artificially imposed electromagnetic field pulses to mimic substorm dipolarization and associated inductive electric field. Several substorm dipolarizations and injections are reproduced in the MHD model, in agreement with the timing of shape changes in the AE/AL index. The associated inductive electric field transports plasma sheet plasma to geostationary altitudes, providing the boundary plasma source to the ring current model. It is found that impulsive plasma sheet injections, together with a large‐scale convection electric field, are necessary to develop a strong ring current. Comparisons with Van Allen Probes observations show that our model reasonably well captures dispersed electron injections and the global Dst index.

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Section: Resultsmentioning

confidence: 72%

The role of ring current particle injections: Global simulations and Van Allen Probes observations during 17 March 2013 storm

Jordanova

Welling

et al. 2014

Geophysical Research Letters

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“…Chi et al [] also showed that proton auroral intensification at the onset of substorm and proton injection at the geosynchronous altitude can occur at the same magnetic local time (longitude). Weygand et al [] demonstrated that the intensification of the westward auroral electrojet and the “dispersionless” particle injection can occur at about (within the uncertainty of the averages) the same time. Despite the geosynchronous injections and AL intensification, the substorm at 2033 IST in the present case does not seem to be associated with any sudden change in the solar wind parameters.…”

Section: Discussionmentioning

confidence: 99%

Three different types of electric field disturbances affecting equatorial ionosphere during a long‐duration prompt penetration event

et al. 2015

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Coordinated digisonde and OI 630.0 nm airglow observations from Thumba (TVM), an Indian dip equatorial station, in conjunction with magnetic and geosynchronous particle flux measurements, reveal three different types of electric field disturbances in the equatorial ionosphere-thermosphere system (ITS) occurring in succession over a period of 6 h on a single night (22-23 January,2012; A p = 24). These include (1) westward electric field perturbations owing to a pseudo-breakup and a substorm event, each lasting for about 30 min; (2) eastward electric field perturbations continuing for about an hour, owing to the southward excursion of Z component of interplanetary magnetic field (B z ); and (3) DP2-type fluctuating (period ∼40 min) electric field perturbation sustaining for about 4 h. The pseudo-breakup and the fully grown substorm events are found to be longitudinally localized and different in terms of response in the westward auroral electrojet index (AL) as well as geosynchronous electron/proton injections. The polarity of the prompt penetration of interplanetary electric field that affects the equatorial ionosphere is observed to be eastward during 2100-2200 IST (Indian Standard Time) which is observationally sparse but consistent with modeling studies. Interestingly, on the same night, DP2-type electric field fluctuations with ∼40 min periodicity and occasional eastward polarity (akin to daytime) are also found to affect the equatorial ITS for about 4 h (2200-0200 IST). The case study, thus, brings out different processes that constitute a long duration prompt penetration event which, otherwise, would have been categorized as a single event.

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“…During this storm the provisional Dst index shown in Figure a dipped to a minimum of −120 nT. The main phase of the storm was characterized by a series of plasma injections manifest in Figure a as variations in the AE index [ Weygand et al ., ]. These continued into the recovery phase albeit with reduced frequency and intensity.…”

Section: Observationsmentioning

confidence: 99%

Broadband low‐frequency electromagnetic waves in the inner magnetosphere

et al. 2015

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A prominent yet largely unrecognized feature of the inner magnetosphere associated with particle injections, and more generally geomagnetic storms, is the occurrence of broadband electromagnetic field fluctuations over spacecraft frame frequencies (fsc) extending from effectively zero to fsc ≳ 100 Hz. Using observations from the Van Allen Probes we show that these waves most commonly occur premidnight but are observed over a range of local times extending into the dayside magnetosphere. We find that the variation of magnetic spectral energy density with fsc obeys εB=Afsc−α over several decades with a spectral breakpoint at fb ≈ 1 Hz. The values for α are lognormally distributed with α = 1.9 ± 0.6 for fsc < fb and α = 2.9 ± 0.6 for fsc > fb. A is a function of geomagnetic activity with the largest values observed over intervals of decreasing Dst index during the main phase of geomagnetic storms. At these times these waves are nearly always present in the nightside inner magnetosphere and are commonly observed from L = 3 outward. The observed variation of the electric to magnetic field amplitude with fsc is well described by a dispersive Alfvén wave model under the assumption that fsc is primarily a consequence of the Doppler shift of plasma frame structures moving over the spacecraft. The robust anticorrelation between the time rate change of the Dst index and wave spectral energy density coupled with the ability of dispersive Alfvén waves to drive transverse ion acceleration suggests that these waves may boost ion energy density in the inner magnetosphere and intensify the ring current during storm times.

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Relation of auroral substorm onset to local AL index and dispersionless particle injections

Cited by 14 publications

References 33 publications

The role of ring current particle injections: Global simulations and Van Allen Probes observations during 17 March 2013 storm

The role of ring current particle injections: Global simulations and Van Allen Probes observations during 17 March 2013 storm

Three different types of electric field disturbances affecting equatorial ionosphere during a long‐duration prompt penetration event

Broadband low‐frequency electromagnetic waves in the inner magnetosphere

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