Quiet time observations of the open‐closed boundary prior to the CIR‐induced storm of 9 August 2008

Urban, K. D.; Gerrard, A. J.; Bhattacharya, Y.; Ridley, A. J.; Lanzerotti, L. J.; Weatherwax, A. T.

doi:10.1029/2011sw000688

Cited by 15 publications

(18 citation statements)

References 44 publications

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“…The 5 mHz frequency is also consistent with experimental magnetometric estimates of the lowest resonant frequency of magnetic field lines [Anderson et al, 1989;Lanzerotti et al, 1999;Urban et al, 2011]. This allows us to assume that quarter-wave oscillations were not excited because of sufficiently high ionospheric conductivity despite winter conditions in the polar ionosphere of the Northern Hemisphere.…”

Section: Discussionsupporting

confidence: 72%

“…On the basis of current conceptions of the formation of the observed background of ULF oscillations by magnetosonic waves coming from the magnetopause deep into the magnetosphere, when taking into account the good agreement of the minimum resonant absorption frequency with the frequencies of standing Alfvén waves in the last closed magnetospheric field line [Lanzerotti et al, 1999;Urban et al, 2011] and considering the fact that the data analysis we carried out has not revealed an increase in the minimum frequency of resonant absorption in the transition from polar radar beams to equatorial ones, we can assume that the minimum resonant frequency found corresponds to the longest magnetic field lines, which are located near the magnetopause in the dayside magnetosphere. However, the presence of intramagnetospheric ULF sources, associated, for example, with energetic particles, can cast doubt on this conclusion, and the question concerning applicability and generality of the assumption remains largely open.…”

Section: Discussionmentioning

confidence: 99%

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Resonant ULF absorption in storm time conditions

Бадин¹

2017

Solar-Terrestrial Physics

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_____________________________________________________________________________________________ INTRODUCTIONThe origin of ultralow-frequency (ULF) oscillations of magnetic and electric fields is often associated with the excitation of magnetohydrodynamic (MHD) resonances in near-Earth plasma frozen in the geomagnetic field. In [Chen, Hasegawa, 1974;Southwood, 1974], the authors theoretically analyze the excitation of resonant ULF oscillations of magnetic field lines by surface MHD waves in the magnetosphere. Resonant frequencies of such oscillations have been repeatedly calculated by numerical methods for both dipole [Lee, Lysak, 1989] and nondipole geomagnetic field models [Cheng, Zaharia, 2003]. The numerical calculations established typical values of minimum resonant frequencies 3-5 mHz (in the dayside magnetosphere) for quiet geomagnetic conditions. A significant limitation of such studies was the approximation of infinitely large ionospheric conductivity. This approximation restricts field line resonances only to eigenoscillations of the so-called classical half-wave mode, i.e. to standing waves for which an integer of half-waves fits between conjugated ionospheres along magnetic field lines. In this case, resonant oscillations of the magnetic field line are analogous to acoustic oscillations of a string whose ends are fixed in the E layer of the conjugated ionospheres [Nishida, 1980]. Taking the finite ionospheric conductivity into account revealed first and foremost a significant damping decrement of the fundamental harmonic of the half-wave mode for sufficiently low ionospheric conductivity [Newton et al., 1978]. In addition, the finite ionospheric conductivity supplemented field line resonances with quarter-wave oscillations, for which an odd number of quarter wavelengths fits between the conjugated ionospheres [Allan, Knox, 1979]. Such oscillations are similar to acoustic oscillations of a pipe whose one end is fixed and the The differences between the experimental and theoretical estimates can be explained by a strong effect of nondissipative energy losses on the Q factor of the resonator [Poulter, Allan, 1985]. At high latitudes, i.e. at L~10 and at low ionospheric conductivity under polar winter conditions, the theoretical Q-factor estimate taking into account only ohmic dissipation [Yumoto et al., 1995] gives Q 1~1 . At high latitudes, there appear additional non-dissipative losses produced, for example, by magnetospheric convection. Indeed, convection trajectories in the general case do not coincide with constant-period magnetic surfaces of the field line resonance. In the drift motion, magnetospheric plasma along with field-aligned currents leaves the resonance region. This causes additional losses of resonator energy and reduces the Q factor. With a low Q factor of the resonator, the eigenoscillation amplitude does not exceed the amplitude of background waves; this hinders the observation of resonant ULF oscillations at high latitudes.High oscillation amplitudes at 2.7, 3.5, and 3.9 mHz, found in...

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Section: Discussionsupporting

confidence: 72%

Section: Discussionmentioning

confidence: 99%

Resonant ULF absorption in storm time conditions

Бадин¹

2017

Solar-Terrestrial Physics

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“…Therefore, it still has to be comprehended why the response to the magnetosheath turbulence driving is displaced from the magnetosheath/magnetosphere interface. Moreover, dayside narrowband Pc5 pulsations, located even deeper in the magnetosphere than broadband Pc5-6, can hardly be associated with oscillations of last closed field lines, as had been suggested by Lanzerotti et al (1999) and Urban et al (2011). It is worth noticing that in the same period scale as Pc5-6 pulsations, there is a class of impulsive/transient disturbances, traveling convection vortices (TCVs), which are commonly observed in the prenoon sector.…”

Section: Annmentioning

confidence: 99%

“…The distinction between broadband and band-limited wave activity was suggested to characterize the location of the open-closed field line boundary (OCB). For synoptic monitoring of the OCB, Urban et al (2011) used a meridional array of Antarctic magnetometers, and retrieved a nominal Pc5 mode with periods T ∼ 3-9 min and long-period modes with T > 10 min. They assumed that isolated Pc5 presence corresponds to closed dayside field lines, whereas high power in both bands indicated that a close magnetotail field line was being sampled.…”

Section: Pilipenko Et Al: Are Dayside Long-period Pulsations Relamentioning

confidence: 99%

Are dayside long-period pulsations related to the cusp?

et al. 2015

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Abstract.We compare simultaneous observations of longperiod ultra-low-frequency (ULF) wave activity from a Svalbard/IMAGE fluxgate magnetometer latitudinal profile covering the expected cusp geomagnetic latitudes. Irregular Pulsations at Cusp Latitudes (IPCL) and narrowband Pc5 waves are found to be a ubiquitous element of ULF activity in the dayside high-latitude region. To identify the ionospheric projections of the cusp, we use the width of return signal of the Super Dual Auroral Radar Network (SuperDARN) radar covering the Svalbard archipelago, predictions of empirical cusp models, augmented whenever possible by Defense Meteorological Satellite Program (DMSP) identification of magnetospheric boundary domains. The meridional spatial structure of broadband dayside Pc5-6 pulsation spectral power has been found to have a localized latitudinal peak, not under the cusp proper as was previously thought, but several degrees southward from the equatorward cusp boundary. The earlier claims of the dayside monochromatic Pc5 wave association with the open-closed boundary also seems doubtful. Transient currents producing broadband Pc5-6 probably originate at the low-latitude boundary layer/central plasma sheet (LLBL/CPS) interface, though such identification with available DMSP data is not very precise. The occurrence of broadband Pc5-6 pulsations in the dayside boundary layers is a challenge to modelers because so far their mechanism has not been firmly identified.Keywords. Ionosphere (ionosphere-magnetosphere interactions) -magnetospheric physics (magnetopause cusp and boundary layers; MHD waves and instabilities)

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“…They noted that similar Pc6 band pulsations did not appear in the variations of the IMF. It is possible they were observing Pc5‐6 resonances on extended closed field lines [ Mathie and Mann , ; Urban et al , ]. Alternatively, Wolfe et al [] argued that the hydromagnetic ULF waves they observed—large‐amplitude (10–20 nT) Pc5 waves—occurred on open field lines.…”

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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Quiet time observations of the open‐closed boundary prior to the CIR‐induced storm of 9 August 2008

Cited by 15 publications

References 44 publications

Resonant ULF absorption in storm time conditions

Resonant ULF absorption in storm time conditions

Are dayside long-period pulsations related to the cusp?

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

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