Bifurcated Region 2 Field‐Aligned Currents Associated With Substorms

Sangha, Harneet K.; Milan, S. E.; Carter, J. A.; Fogg, Alexandra Ruth; Anderson, B. J.; Korth, H.; Paxton, L. J.

doi:10.1029/2019ja027041

Cited by 9 publications

(16 citation statements)

References 46 publications

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“…However, Knipp et al (2021) also mention the possible importance of the fact that the field-aligned current configurations appear to be different in the two hemispheres, citing studies by Coxon et al (2016), Shi et al (2020), andSangha et al (2020). These findings are consistent with our finding that the two-cell convection pattern is more distinct in the NH, as can be seen in Figure 3, and a similar finding has been made by Förster and Haaland (2015).…”

Section: Discussionsupporting

confidence: 90%

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Violation of Hemispheric Symmetry in Integrated Poynting Flux via an Empirical Model

Cosgrove

Bahcivan

Chen

et al. 2022

Geophysical Research Letters

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Empirical models of the incident Poynting flux (PF), associated with auroral processes, have been separately constructed for the northern and southern hemispheres using data from the Fast Auroral SnapshoT (FAST) satellite (Carlson et al. (1998)). The models are constructed by fitting a set of basis functions to the PF measured by the electric and magnetic field sensors on board FAST (Ergun et al. (2001);Elphic et al. (2001)), where the basis function coefficients are expressed as quadratic equations in a chosen set of geophysical parameters. The modeling methodology was explained in detail by Cosgrove et al. (2014), and has changed very little. Basis functions are constructed from the data as empirical orthogonal functions, and are used to describe variations from a background state that is essentially an IMF-average. However, the lead author has recently put the data itself through a process of quality control that has reduced the number of orbits deemed useable from 8,085 to 7,301 for the NH, and from 5,501 to 4,953 for the SH, with the benefit of providing additional confidence in the results presented here (which were noted earlier, but not published). Some details concerning the quality control process are given in the Supporting Information S1.The models output flux maps for the regions above 60° magnetic latitude (MLAT) and below − 60° MLAT as a function of (a) clock angle of the interplanetary magnetic field (IMF), (b) magnitude of the IMF in the GSM y-z

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Section: Discussionsupporting

confidence: 90%

“…( 2020 ), and Sangha et al. ( 2020 ). These findings are consistent with our finding that the two‐cell convection pattern is more distinct in the NH, as can be seen in Figure 3 , and a similar finding has been made by Förster and Haaland ( 2015 ).…”

Section: Discussionmentioning

confidence: 96%

Violation of Hemispheric Symmetry in Integrated Poynting Flux via an Empirical Model

Cosgrove

Bahcivan

Chen

et al. 2022

Geophysical Research Letters

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“…Shi et al (2020) show that mean NH AMPERE-derived R1 currents are stronger in the dusk to early-afternoon region. Sangha et al (2020) show a strong NH-preference for bifurcated substorm Region 2 (R2) FACs that may also contribute to the dusk asymmetry. The PF asymmetry in Figure 2 scales with geomagnetic activity near dusk and may indicate a mix of dynamic (Alfvenic) and quasi-steady PF signatures.…”

Section: Discussionmentioning

confidence: 99%

Hemispheric Asymmetries in Poynting Flux Derived From DMSP Spacecraft

Knipp

Kilcommons

Hairston

et al. 2021

Geophysical Research Letters

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The first satellites launched to low Earth orbit (LEO) sparked a flurry of speculation about the energy sources for Earth's heated upper atmosphere. Cole (1962) asserted that Joule heating of the upper atmosphere could explain the fluctuations in orbital acceleration during geomagnetic disturbances. Sugiura (1984, 1986) deduced that high-latitude electric field, E, magnetic field, B, and their variations dB, and dE, reported by the Dynamics Explorer-2 (DE-2) mission during a magnetic storm in 1981 were consistent with electromagnetic energy transfer via the Poynting vector and that the transfer was equal to the ionospheric energy (Joule) dissipation below the satellite. Subsequent investigations have considered the Poynting vector, also called Poynting flux (PF), as a source of thermospheric disturbances. The requirement for simultaneous full-component B, E, dB, and dE measurements over a range of frequencies and locations has frustrated attempts to systematically quantify PF response to geospace disturbances. Knudsen (1990) and Kelley et al. (1991) applied Poynting's theorem to HILAT spacecraft measurements (altitude ∼800 km) of the convective electric field, E and magnetic perturbations dB relative to Earth's main field. They calculated electromagnetic energy transfer as:

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“…These data are used to constrain a spherical harmonic fit, from which the FAC density can be computed (Anderson et al, 2000;Waters et al, 2001;Green et al, 2006;Coxon et al, 2014a, Coxon et al, 2014b, Coxon et al, 2018. Sangha et al (2020) discussed the dawn-dusk and interhemispheric variabilities between the occurrences of the R2Bs. An initial analysis of the seasonal occurrence distribution was also discussed.…”

Section: Instrumentationmentioning

confidence: 99%

“…They are also associated with the region of low ionospheric conductance. They suggest that these R2Bs are the closure currents associated with SAPS (Foster and Burke 2002;Huang et al, 2006;Clausen et al, 2012;Lejosne and Mozer 2017;Sangha et al, 2020).…”

Section: Introductionmentioning

confidence: 99%

Statistical Analysis of Bifurcating Region 2 Field-Aligned Currents Using AMPERE

Sangha

Milan

Anderson

et al. 2022

Front. Astron. Space Sci.

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We present a statistical analysis of the occurrence of bifurcations of the Region 2 (R2) Field-Aligned Current (FAC) region, observed by the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE). Previously, these have been shown to occur as the polar cap contracts after substorm onset, the beginning of the growth phase. During this phase both the Region 1 (R1) and R2 currents move equatorwards as the polar cap expands. Following onset, the R1 FAC region contracts polewards but the R2 FAC continues to expand equatorwards before eventually fading. At the same time, a new R2 FAC develops equatorwards of the R1 FAC. We have proposed that the bifurcated FACs formed during substorms are associated with plasma injections from the magnetotail into the inner magnetosphere, and that they might be the FAC signature associated with Sub-Auroral Polarization Streams (SAPS). We investigate the seasonal dependence of the occurrence of bifurcations from 2010 to 2016, determining whether they occur predominantly at dawn or dusk. Region 2 Bifurcations (R2Bs) are observed most frequently in the summer hemisphere and at dusk, and we discuss the possible influence of ionospheric conductance. We also discuss a newly discovered UT dependence of the R2B occurrences between 2011 and 2014. This dependence is characterized by broad peaks in occurrence near 09 and 21 UT in both hemispheres. Reasons for such a preference in occurrence are explored.

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Bifurcated Region 2 Field‐Aligned Currents Associated With Substorms

Cited by 9 publications

References 46 publications

Violation of Hemispheric Symmetry in Integrated Poynting Flux via an Empirical Model

Violation of Hemispheric Symmetry in Integrated Poynting Flux via an Empirical Model

Hemispheric Asymmetries in Poynting Flux Derived From DMSP Spacecraft

Statistical Analysis of Bifurcating Region 2 Field-Aligned Currents Using AMPERE

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