Isolated bursts of irregular geomagnetic pulsations in the region of the dayside cusp

Kurazhkovskaya, N. A.; Klain, B. I.

doi:10.1134/s0016793217040119

“…The high‐latitude transient MIEs and Pc5 pulsations can be triggered by solar wind pressure jumps (Friis‐Christensen et al, ), impulsive reconnection at the magnetopause (Bolshakova & Troitskaya, ; Lanzerotti & MacLennan, ), hot flow anomalies (Murr & Hughes, ), and ion foreshock transients (Hartinger et al, ; Shen et al, ). The broadband fluctuations in the region of the dayside cusp can be a manifestation of MHD intermittent turbulence of the magnetosheath (Kurazkovskaya & Klain, ), or shear instability at the reversal boundary of ionospheric convection associated with the LLBL (Clauer et al, ). Magnetosheath plasma jets can excite transient waves with discrete frequencies in the subsolar magnetosphere (Archer et al, b).…”

Section: Introductionmentioning

confidence: 99%

Transient Oscillations Near the Dayside Open‐Closed Boundary: Evidence of Magnetopause Surface Mode?

Козырева

¹

,

Pilipenko

²

,

Lorentzen

³

et al. 2019

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Geomagnetic pulsations in Pc5-6 band (~3-20 min) are persistent feature of ULF activity at dayside high latitudes. Magnetopause surface eigenmodes may be suggested as potential mechanism of these pulsations. One might expect the ground response of these modes to be near ionospheric projection of the open-closed field line boundary (OCB). Using data from instruments located at Svalbard we study transient geomagnetic response to impulsive "intrusion" of magnetosheath plasma into the dayside magnetosphere. These intrusions are triggered by modest changes of interplanetary magnetic field to southward, and observed as sudden shifts of equatorward red aurora boundary to lower latitudes and green line emission intensification. Each auroral disturbance is accompanied by burst of~1.7-2.0-mHz geomagnetic pulsations. Near-cusp latitudinal structure of ULF pulsations is compared with instant location of equatorward boundary of the red aurora, assumed to be a proxy of the OCB. Optical OCB latitude has been identified using data from the meridian scanning photometer. The latitudinal maximum of the transient geomagnetic response tends to be located near disturbed OCB proxy, within the error~1°-2°of the photometer and magnetometer methods. Recorded transient pulsations may be associated with the ground image of the magnetopause surface mode harmonic. Theoretical consideration indicates that after an initial excitation, surface large-scale mode converts into localized Alfvén oscillations and thus can exist for limited time only. Therefore, MHD surface modes in realistic inhomogeneous plasma cannot be considered in isolation, but as a combined system of modes with discrete and continuous spectra with irreversible transformation between them.

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“…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%

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

Potapov

¹

,

Guglielmi

²

,

Dovbnya

³

2020

Solar-Terrestrial Physics

2

0

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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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“…Это, во-первых, доли геомагнитного хвоста, проецирующиеся в полярные шапки; вовторых, полярные каспы и клефты с полуденной стороны полярной шапки (от ±65° до 70° геомагнитной широты), где силовые линии, уходящие в хвост, граничат с линиями, соединяющимися с магнитошитом (каспы) или низкоширотным пограничным слоем (клефты) [Farrell, van Allen, 1990]. С этими структурами связаны процессы, влияющие на динамику магнитосферы: дневное магнитное пересоединение, прямое проникновение волновой турбулентности и плазмы из солнечного ветра (СВ) и магнитошита [Sauvaud et al, 1998;Berthomier et al, 2004;, магнитные импульсы (MIE) и иррегулярные пульсации (IPCL) [Lanzerotti et al, 1991;Yahnin et al, 1995;Sibeck, Korotova, 1996;Kurazhkovskaya, Klain, 2017;Гульельми и др., 2017].…”

Section: Introductionunclassified

Ultra low frequency emissions ranging from 0.1 to 3 Hz in circumpolar areas

Потапов

¹

,

Guglielmi

²

,

Dovbnya

³

2020

Solnechno-Zemnaya Fizika

1

0

View full text Add to dashboard Cite

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.

show abstract

Isolated bursts of irregular geomagnetic pulsations in the region of the dayside cusp

Cited by 4 publications

References 15 publications

Transient Oscillations Near the Dayside Open‐Closed Boundary: Evidence of Magnetopause Surface Mode?

Transient Oscillations Near the Dayside Open‐Closed Boundary: Evidence of Magnetopause Surface Mode?

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

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