Diagnosing the Role of Alfvén Waves in Global Field‐Aligned Current System Dynamics During Southward IMF: Swarm Observations

Pakhotin, Ivan; Mann, I. R.; Knudsen, D. J.; Lysak, R. L.; Burchill, J. K.

doi:10.1029/2019ja027277

Cited by 16 publications

(16 citation statements)

References 60 publications

(152 reference statements)

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“…Stronger NH FACS, as reported here, would also support stronger NH closing currents. Pakhotin et al (2019Pakhotin et al ( , 2020 argued that dB and FACs with scales < ~ 150 km are more appropriately treated as incident, ionospherically reflected, and interfering Alfvén waves. In their view, an Alfvén wave paradigm could/should be used to accurately describe the entire spectrum of scale sizes involved in MI coupling.…”

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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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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show abstract

“…Previous work has shown that to some degree, similar behaviour can be inferred in terms of FACs 12 which must logically be associated with these electromagnetic perturbations as well—especially since they are related to Alfvén wave dynamics. For example, previous observational studies have made the link between Alfvénic disturbances and FACs, and have suggested that both may be explained as part of the same physical framework which can explain the characteristics of MIC at these scales 17 , 24 , 27 , 28 . This study is the first to demonstrate that, when seasonally averaged, the high-latitude electromagnetic Poynting flux observed across a wide range of scales has a definitive northern preference both on the dayside and on the nightside.…”

Section: Discussionmentioning

confidence: 99%

“…Meanwhile on the dayside, the southern oval also similarly experiences more variation in solar illumination than the north, potentially traversing further into and dwelling longer in sunlit dayside regions where there is expected to be a greater mismatch between the Pedersen and Alfvén impedances as a result of increased background Pedersen conductance due to dayside solar EUV illumination. This would be expected to lead to greater median Alfvén wave ionospheric reflection coefficients in the south, as per the ionospherically reflecting Alfvén wave paradigm 16,17,23,24 . In turn this could lead to a stronger reflection of Poynting flux from the southern ionosphere back towards the equator than in the north.…”

Section: Discussionmentioning

confidence: 99%

Northern preference for terrestrial electromagnetic energy input from space weather

Mann

Xie

et al. 2021

Nat Commun

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Terrestrial space weather involves the transfer of energy and momentum from the solar wind into geospace. Despite recently discovered seasonal asymmetries between auroral forms and the intensity of emissions between northern and southern hemispheres, seasonally averaged energy input into the ionosphere is still generally considered to be symmetric. Here we show, using Swarm satellite data, a preference for electromagnetic energy input at 450 km altitude into the northern hemisphere, on both the dayside and the nightside, when averaged over season. We propose that this is explained by the offset of the magnetic dipole away from Earth’s center. This introduces a larger separation between the magnetic pole and rotation axis in the south, creating different relative solar illumination of northern and southern auroral zones, resulting in changes to the strength of reflection of incident Alfvén waves from the ionosphere. Our study reveals an important asymmetry in seasonally averaged electromagnetic energy input to the atmosphere. Based on observed lower Poynting flux on the nightside this asymmetry may also exist for auroral emissions. Similar offsets may drive asymmetric energy input, and potentially aurora, on other planets.

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“…Previous work has shown that to some degree, similar behaviour can be inferred in terms of FACs 12 which must logically be associated with these electromagnetic perturbations as well-especially since they are related to Alfvén wave dynamics. For example, previous observational studies have made the link between Alfvénic disturbances and FACs, and have suggested that both may be explained as part of the same physical framework which can explain the characteristics of MIC at these scales 17,24,27,28 . This study is the first to demonstrate that, when seasonally averaged, the high-latitude electromagnetic Poynting flux observed across a wide range of scales has a definitive northern preference both on the dayside and on the nightside.…”

Section: Discussionmentioning

confidence: 99%

Northern Preference for Terrestrial Electromagnetic Energy Input from Space Weather

Pakhotin

Mann

Xie

et al. 2020

Preprint

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Terrestrial space weather involves the transfer of energy and momentum from the solar wind into geospace. Despite recently discovered seasonal asymmetries between auroral forms and the intensity of emissions between northern and southern hemispheres, seasonally averaged energy input into the ionosphere is still generally considered to be symmetric. Here we show, using Swarm satellite data, a preference for electromagnetic energy input at 450 km altitude into the northern hemisphere, on both the dayside and the nightside, when averaged over season. We propose that this is explained by the offset of the magnetic dipole away from Earth's center. This introduces a larger separation between the magnetic pole and rotation axis in the south, creating different relative solar illumination of northern and southern auroral zones, resulting in changes to the strength of reflection of incident Alfvén waves from the ionosphere. Our study reveals an important asymmetry in seasonally averaged electromagnetic energy input to the atmosphere. Based on observed lower Poynting flux on the nightside this asymmetry may also exist for auroral emissions. Similar offsets may drive asymmetric energy input, and potentially aurora, on other planets.

show abstract

Diagnosing the Role of Alfvén Waves in Global Field‐Aligned Current System Dynamics During Southward IMF: Swarm Observations

Cited by 16 publications

References 60 publications

Hemispheric Asymmetries in Poynting Flux Derived From DMSP Spacecraft

Hemispheric Asymmetries in Poynting Flux Derived From DMSP Spacecraft

Northern preference for terrestrial electromagnetic energy input from space weather

Northern Preference for Terrestrial Electromagnetic Energy Input from Space Weather

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