North-south asymmetry of ultra-low-frequency oscillations of Earth’s electromagnetic field

Guglielmi, A. V.; Klain, B. I.; Potapov, A. S.

doi:10.12737/stp-34201703

Cited by 6 publications

(8 citation statements)

References 16 publications

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“…Besides, as has been shown previously [Guglielmi et al, 2019], the DS occurrence rate also depends on the vertical inclination of the IMF vector (but not on the sign of B z ) determining the foreshock orientation. Thus, there is reason to assume that the signals are generated in a foreshock or even ahead of it in SW, and with a favorable relative position of the IMF vector, the magnetic field line passing through the observation station, and the magnetic dipole tilt they penetrate into Earth's surface.…”

Section: Discussionsupporting

confidence: 54%

“…We have already examined DS that occur in the polar areas in [Guglielmi et al, 2019]. In that paper, we have found that the signal occurrence rate depends on the orientation of the interplanetary magnetic field (IMF) in the XOZ plane.…”

Section: Discrete Frequency-dispersed Signalsmentioning

confidence: 99%

“…In this case, the best conditions for observing DS exist when this field line is sunward. This may be due to the fact that the ULF pulses, excited in the foreshock or on the boundary of the magnetosphere, falling on external geomagnetic field lines slide along them into cusps, which are attractors for the waves incident from SW on the magnetopause [Guglielmi et al, 2017]. At magnetic noon, the magnetic dipole axis and the southern cusp funnel most strongly incline toward SW, especially in November-January.…”

Section: Discrete Frequency-dispersed Signalsmentioning

confidence: 99%

“…These are, firstly, geomagnetic tail lobes projecting to the polar caps; secondly, polar cusps and clefts on the noon side of the polar cap (from ±65to 70of geomagnetic latitude), where the field lines going into the tail border the lines connecting with the magnetosheath (cusps) or with the low-latitude boundary layer (clefts) [Farrell, van Allen, 1990]. These structures are associated with the processes affecting the magnetosphere dynamics: dayside magnetic reconnection, direct penetration of wave turbulence and plasma from the solar wind (SW) and magnetosheath [Sauvaud et al, 1998;Berthomier et al, 2004;Moiseev et al, 2015], magnetic pulses (MIE), and irregular pulsations (IPCL) [Lanzerotti et al, 1991;Yahnin et al, 1995;Sibeck, Korotova, 1996;Manweiler et al, 2018;Kurazhkovskaya, Klain, 2017;Guglielmi et al, 2017].…”

Section: Introductionmentioning

confidence: 99%

“…Dynamic spectrum of a discrete signal with a negative slope to the time axis, recorded at the station Vostok[Guglielmi et al, 2019] …”

mentioning

confidence: 99%

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ULTRA LOW FREQUENCY EMISSIONS RANGING FROM 0.1 TO 3 Hz IN CIRCUMPOLAR AREAS

Potapov

Guglielmi

Dovbnya

2020

Solar-Terrestrial Physics

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We examine the characteristics of oscillations of two types in the high-frequency edge of the ULF range (0.1–3 Hz), serpentine emission (SE), and discrete frequency dispersed signals (DS). Oscillations of both the types are observed in the polar caps exclusively with induction magnetometers. Since these instruments are currently practically absent at high latitudes, the analysis has been carried out from records obtained at the stations Vostok and Thule close to the geomagnetic poles in 1968–1971. The DS occurrence rate is shown to have a sharp peak at local magnetic noon. This fact indicates that DS emergence is rigidly tied to the geomagnetic field line passing through the observation station. At the same time, the seasonal variation in the frequency of DS occurrence has a main peak in local summer and an additional peak in local winter. We have revealed before that at least a part of DS is excited in the foreshock region. Taking this into account, we can assume that the wave packets incident to the magnetopause fall on the external field lines mainly in the noon region and propagate along these lines in both directions, eventually reaching Earth’s surface in the polar regions. Unlike DS, the SE occurrence rate has neither a daily nor a seasonal variation. We have tested and confirmed indirectly the hypothesis put forward earlier about the excitation of SE by cyclotron instability of protons in the solar wind, simulating frequency variations in ion-cyclotron waves at different levels of interplanetary plasma perturbation and comparing the results with the SE frequency variations observed under similar conditions. We conclude that it is necessary to resume continuous observations of ULF emissions, using induction magnetometers installed in polar caps near the projections of cusps and near geomagnetic poles.

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Section: Discussionsupporting

confidence: 54%

Section: Discrete Frequency-dispersed Signalsmentioning

confidence: 99%

Section: Discrete Frequency-dispersed Signalsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…Dynamic spectrum of a discrete signal with a negative slope to the time axis, recorded at the station Vostok[Guglielmi et al, 2019] …”

mentioning

confidence: 99%

See 3 more Smart Citations

ULTRA LOW FREQUENCY EMISSIONS RANGING FROM 0.1 TO 3 Hz IN CIRCUMPOLAR AREAS

Potapov

Guglielmi

Dovbnya

2020

Solar-Terrestrial Physics

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Multi-point Conjugate Observations of Dayside ULF Waves during an Extended Period of Radial IMF

Shi

Hartinger

Baker

et al. 2020

Preprint

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Long-lasting Pc5 ultralow frequency (ULF) waves spanning the dayside and extending from L ∼ 5.5 into the polar cap region were observed by conjugate ground magnetometers. Observations from MMS satellites in the magnetosphere and magnetometers on the ground confirmed that the ULF waves on closed field lines were due to fundamental toroidal standing Alfvén waves. Monochromatic waves at lower latitudes tended to maximize their power away from noon in both the morning and afternoon sectors, while more broadband waves at higher latitudes tended to have a wave power maximum near noon. The wave power distribution and MMS satellite observations during the magnetopause crossing indicate surface waves on a Kelvin-Helmholtz (KH) unstable magnetopause coupled with standing Alfvén waves. The more turbulent ion foreshock during an extended period of radial interplanetary magnetic field (IMF) likely plays an important role in providing seed perturbations for the growth of the KH waves. These results indicate that the Pc5 waves observed on closed field lines and on the open field lines of the polar cap were from the same source.Plain Language Summary The Earth's magnetic field lines can oscillate at ultralow frequencies (ULF: 1 mHz to 5 Hz). These natural oscillations of closed magnetic field lines, analogous to vibrations on a stretched string, are also called geomagnetic pulsations or ULF waves. ULF waves play a key role in the transfer of energy from terrestrial space to Earth's upper atmosphere. In this study, we report a long-lasting large spatial scale ULF wave event observed by ground observatories from both hemispheres. Together with satellite measurements in space, we are able to confirm that these waves were driven by upstream turbulent structures due to the interaction between matter and electromagnetic fields emitted from the Sun and the Earth's outer atmosphere and magnetic field.

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Multipoint Conjugate Observations of Dayside ULF Waves During an Extended Period of Radial IMF

et al. 2020

View full text Add to dashboard Cite

Long-lasting Pc5 ultralow frequency (ULF) waves spanning the dayside and extending from L ∼ 5.5 into the polar cap region were observed by conjugate ground magnetometers. Observations from MMS satellites in the magnetosphere and magnetometers on the ground confirmed that the ULF waves on closed field lines were due to fundamental toroidal standing Alfvén waves. Monochromatic waves at lower latitudes tended to maximize their power away from noon in both the morning and afternoon sectors, while more broadband waves at higher latitudes tended to have a wave power maximum near noon. The wave power distribution and MMS satellite observations during the magnetopause crossing indicate surface waves on a Kelvin-Helmholtz (KH) unstable magnetopause coupled with standing Alfvén waves. The more turbulent ion foreshock during an extended period of radial interplanetary magnetic field (IMF) likely plays an important role in providing seed perturbations for the growth of the KH waves. These results indicate that the Pc5 waves observed on closed field lines and on the open field lines of the polar cap were from the same source. Plain Language Summary The Earth's magnetic field lines can oscillate at ultralow frequencies (ULF: 1 mHz to 5 Hz). These natural oscillations of closed magnetic field lines, analogous to vibrations on a stretched string, are also called geomagnetic pulsations or ULF waves. ULF waves play a key role in the transfer of energy from terrestrial space to Earth's upper atmosphere. In this study, we report a long-lasting large spatial scale ULF wave event observed by ground observatories from both hemispheres. Together with satellite measurements in space, we are able to confirm that these waves were driven by upstream turbulent structures due to the interaction between matter and electromagnetic fields emitted from the Sun and the Earth's outer atmosphere and magnetic field.

show abstract

North-south asymmetry of ultra-low-frequency oscillations of Earth’s electromagnetic field

Cited by 6 publications

References 16 publications

ULTRA LOW FREQUENCY EMISSIONS RANGING FROM 0.1 TO 3 Hz IN CIRCUMPOLAR AREAS

ULTRA LOW FREQUENCY EMISSIONS RANGING FROM 0.1 TO 3 Hz IN CIRCUMPOLAR AREAS

Multi-point Conjugate Observations of Dayside ULF Waves during an Extended Period of Radial IMF

Multipoint Conjugate Observations of Dayside ULF Waves During an Extended Period of Radial IMF

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