Are dayside long-period pulsations related to the cusp?

Pilipenko, Vyacheslav; Belakhovsky, V. B.; Engebretson, M. J.; Kozlovsky, Alexander; Yeoman, T. K.

doi:10.5194/angeo-33-395-2015

Cited by 17 publications

(9 citation statements)

References 45 publications

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“…Thus, the ULF maximum is shifted ~2° equatorward from the cusp boundary (vertical dashed line). Other events and larger statistics confirming characteristic features presented in this example are discussed in [Pilipenko et al, 2015].…”

Section: Dayside Ocb From Hf Radar and Ulf Activitysupporting

confidence: 77%

Suppression of the dayside magnetopause surface modes

Пилипенко

Pilipenko

Козырева

et al. 2017

Solnechno-Zemnaya Fizika

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Magnetopause surface eigenmodes were suggested as a potential source of dayside high-latitude broadband pulsations in the Pc5-6 band (frequency about 1–2 mHz). However, the search for a ground signature of these modes has not provided encouraging results. The comparison of multi-instrument data from Svalbard with the latitudinal structure of Pc5-6 pulsations, recorded by magnetometers covering near-cusp latitudes, has shown that often the latitudinal maximum of pulsation power occurs about 2–3° deeper in the magnetosphere than the dayside open-closed field line boundary (OCB). The OCB proxy was determined from SuperDARN radar data as the equatorward boundary of enhanced width of a return radio signal. The OCB-ULF correspondence is further examined by comparing the latitudinal profile of the near-noon pulsation power with the equatorward edge of the auroral red emission from the meridian scanning photometer. In most analyzed events, the “epicenter” of Pc5-6 power is at 1–2° lower latitude than the optical OCB proxy. Therefore, the dayside Pc5-6 pulsations cannot be associated with the ground image of the magnetopause surface modes or with oscillations of the last field line. A lack of ground response to these modes beneath the ionospheric projection of OCB seems puzzling. As a possible explanation, we suggest that a high variability of the outer magnetosphere near the magnetopause region may suppress the excitation efficiency. To quantify this hypothesis, we consider a driven field line resonator terminated by conjugate ionospheres with stochastic fluctuations of its eigenfrequency. A solution of this problem predicts a substantial deterioration of resonant properties of MHD resonator even under a relatively low level of background fluctuations. This effect may explain why there is no ground response to magnetopause surface modes or oscillations of the last field line at the OCB latitude, but it can be seen at somewhat lower latitudes with more regular and stable magnetic and plasma structure.

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Section: Dayside Ocb From Hf Radar and Ulf Activitysupporting

confidence: 77%

Suppression of the dayside magnetopause surface modes

Пилипенко

Pilipenko

Козырева

et al. 2017

Solnechno-Zemnaya Fizika

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“…The SuperDARN radar (Pilipenko et al, ) and optical (Pilipenko et al, ) techniques coordinated with a magnetometer latitudinal profile covering the expected cusp latitudes found that the meridional spatial structure of broadband dayside Pc5 pulsation spectral power has a localized latitudinal peak, but not under the cusp proper as was previously thought, but several degrees southward from the equatorward cusp boundary.…”

Section: Introductionmentioning

confidence: 80%

“…Discrimination in the recorded transient response contributions from the discrete mode and the Alfvén continuum mode requires a specialized data analysis technique (Allan et al, ). At the same time, long‐lasting Pc5/IPCL quasi‐periodic oscillations at daytime high latitudes are probably associated with a resonant response of magnetic shells inside the magnetosphere, that is, about several degrees equatorward from OCB (Pilipenko et al, ). The quality factor of the magnetospheric Alfvén resonator in the outer magnetosphere is probably rather low which explains broadband waveforms of these pulsations.…”

Section: Discussionmentioning

confidence: 99%

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

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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“…Later studies have shown that though broadband Pc5‐6/Pi3 ULF activity at high latitudes is often associated with the cusp, it is unlikely that there exist broadband Pc5‐6/Pi3 signatures unique to the cusp/cap boundary or the open/closed field line boundary (OCB) in general [e.g., Engebretson et al , ; Pilipenko and Engebretson , ; Engebretson et al , ; Pilipenko et al , ]. For example, Pilipenko et al [] compared the broadband Pc5‐6/Pi3 maxima along the Svalbard/IMAGE meridian chain of magnetometers (ranging between 67.2°N and 80.9°N CGMLat) to cusp location identifications derived from three independent methods (overhead SuperDARN radar beam data, model prediction [ Newell et al , ], and particle precipitation boundary identifications), showing that the IPCL maxima occur 1–5° equatorward of the cusp. Other studies have demonstrated that instead of irregular, broadband Pc5‐6/Pi3 pulsations, narrowband Pc5‐6 pulsations could possibly indicate this dayside OCB [e.g., McHarg et al , ; Ables et al , ; Lanzerotti et al , ] and possibly on the nightside as well [ Urban et al , ].…”

Section: Introductionmentioning

confidence: 99%

Rethinking the polar cap: Eccentric dipole structuring of ULF power at the highest corrected geomagnetic latitudes

et al. 2016

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The day‐to‐day evolution and statistical features of Pc3‐Pc7 band ultralow frequency (ULF) power throughout the southern polar cap suggest that the corrected geomagnetic (CGM) coordinates do not adequately organize the observed hydromagnetic spatial structure. It is shown that that the local‐time distribution of ULF power at sites along CGM latitudinal parallels exhibit fundamental differences and that the CGM latitude of a site in general is not indicative of the site's projection into the magnetosphere. Thus, ULF characteristics observed at a single site in the polar cap cannot be freely generalized to other sites of similar CGM latitude but separated in magnetic local time, and the inadequacy of CGM coordinates in the polar cap has implications for conjugacy/mapping studies in general. In seeking alternative, observationally motivated systems of “polar cap latitudes,” it is found that eccentric dipole (ED) coordinates have several strengths in organizing the hydromagnetic spatial structure in the polar cap region. ED latitudes appear to better classify the local‐time ULF power in both magnitude and morphology and better differentiate the “deep polar cap” (where the ULF power is largely UT dependent and nearly free of local‐time structure) from the “peripheral polar cap” (where near‐magnetic noon pulsations dominate at lower and lower frequencies as one increases in ED latitude). Eccentric local time is shown to better align the local‐time profiles in the magnetic east component over several PcX bands but worsen in the magnetic north component. It is suggested that a hybrid ED‐CGM coordinate system might capture the strengths of both CGM and ED coordinates. It is shown that the local‐time morphology of median ULF power at high‐latitude sites is dominantly driven by where they project into the magnetosphere, which is best quantified by their proximity to the low‐altitude cusp on the dayside (which is not necessarily quantified by a site's CGM latitude), and that variations in the local‐time morphology at sites similar in ED latitude are due to both geographic local‐time control (relative amplification or dampening by the diurnal variation in the local ionospheric conductivity) and geomagnetic coastal effects (enhanced power in a coastally mediated direction). Regardless of cause, it is emphasized that the application of CGM latitudes in the polar cap region is not entirely meaningful and likely should be dispensed with in favor of a scheme that is in better accord with the observed hydromagnetic spatial structure.

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Are dayside long-period pulsations related to the cusp?

Cited by 17 publications

References 45 publications

Suppression of the dayside magnetopause surface modes

Suppression of the dayside magnetopause surface modes

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

Rethinking the polar cap: Eccentric dipole structuring of ULF power at the highest corrected geomagnetic latitudes

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