The temporal variation of the frequency of high latitude field line resonances

Waters, C. L.; Samson, J. C.; Donovan, E.

doi:10.1029/94ja02712

Cited by 78 publications

(68 citation statements)

References 25 publications

(11 reference statements)

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“…The result of the cross-phase analysis [Waters et al, 1995] between RAN and ESK indicates that one of the resonance frequencies at that latitude was about 3.3 mHz (not shown). Therefore, it is likely that the field line resonance took place near the L shell of RAN; this is consistent with the result of the analysis of the GOES 7 data (section 2.2) that the resonance shell, if it existed, was located outside of geosynchronous orbit and therefore, on the ground, poleward of GIL.…”

Section: Ground Signaturesmentioning

confidence: 99%

Coordinated ISTP satellite and ground observations of morningside Pc5 waves

Ohtani¹,

Rostoker²,

Takahashi³

et al. 1999

J. Geophys. Res.

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Abstract. This paper reports the result of a coordinated data analysis of a morningside Pc5 event observed at different altitudes in the magnetosphere and also on the ground. The event took place during 1400-1500 UT of April 29, 1993. The Geotail satellite was located in the boundary region and observed a 5-min quasi-periodic magnetic oscillation. The oscillation was mostly transverse to the background magnetic field. A 90 ø phase lag between the magnetic field and electric field variations was not clear, suggesting that the oscillation was not a standing wave and that Geotail was located in or close to the excitation region. The plasma flow vector rotated clockwise on the equatorial plane viewed from the north as expected for a magnetospheric surface wave on the morningside. At geosynchronous altitude, the GOES satellites also observed a 5-min magnetic oscillation but with a significantly smaller amplitude than at the Geotail position. Five-minute magnetic oscillations were also detected at Canadian Auroral Network for the OPEN Program Unified Study (CANOPUS) and Magnetometer Array for Cusp and Cleft Studies (MACCS) ground stations in the same local time sector as the satellites, even equatorward of a region 2 field-aligned current observed by the Freja magnetometer data. From the phase analysis of ground signatures, the wave is inferred to propagate westward (antisunward) at a velocity of 18 ø in longitude per minute. The propagation speed mapped to the equator, 400 km/s, is in the range of the expected flow speed of the magnetosheath. It is inferred that in the present event, the Kelvin-Helmholtz instability at the magnetopause, rather than at the inner edge of the boundary layer, excited an oscillation at the single frequency in a large area from the boundary region to deep inside the magnetosphere.

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Section: Ground Signaturesmentioning

confidence: 99%

Coordinated ISTP satellite and ground observations of morningside Pc5 waves

Ohtani¹,

Rostoker²,

Takahashi³

et al. 1999

J. Geophys. Res.

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“…A more exact method for computing field line eigenfrequencies was derived by Singer et al [1981]. The Singer et al [1981] method was then used by considering more and more sophisticated models of the magnetospheric field: Olson-Pftizer model [Walker, 1979;Singer et al, 1981], T87 model [Tsyganenko, 1987;Waters et al, 1995], T89 model [Tsyganenko, 1989;Takahashi et al, 2002], T96 model [Tsyganenko, 1995;Takahashi et al, 2004Takahashi et al, , 2006, T01 model [Tsyganenko, 2002;Berube et al, 2006;Kale et al, 2009], and TS05 model [Tsyganenko and Sitnov, 2005;Takahashi et al, 2010].…”

Section: Introductionmentioning

confidence: 99%

Comparison of equatorial plasma mass densities deduced from field line resonances observed at ground for dipole and IGRF models

2014

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The technique to remotely sense the plasma mass density in magnetosphere using field line resonance frequencies detected by ground-based magnetometers has become more and more popular in the last few years. In this paper we examine the error that would be committed at low and middle latitudes (L < 4) in estimating the equatorial plasma mass density if dipole field lines are assumed instead of the more realistic representation given by International Geomagnetic Reference Field (IGRF) lines. It is found that the use of the centered dipole model may result in an error in the inferred density appreciably larger than what is usually assumed. In particular, it has a significant longitudinal dependence being, for example, greater than +30% in the Atlantic sector and about À30% at the opposite longitude sector for field lines extending to a geocentric distance of 2 Earth radii. This may result in an erroneous interpretation of the longitudinal variation in plasmaspheric density when comparing results from ground-based arrays located at different longitudes. We also propose simple modifications of the standard technique, such as the use of an effective dipole moment or the eccentric dipole model, which allow to keep using the dipole field geometry but with a significant error reduction.

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“…On the other hand, in Europe, the two modes show different characteristics: the 1.8 mHz fluctuations are highly coherent over the whole latitudinal range (∼36 • -64 • ) and their power increases monotonically with increasing latitude; conversely, the higher frequency (3.6 mHz) fluctuations are coherent up to NUR (∼57 • ), where their power maximizes; then, between NUR and SOD (∼64 • ), the coherence strongly decreases and at SOD, the frequency is slightly lower and the power decreases. These features might be signatures of a field line resonance at ∼3.6 mHz between NUR and SOD (Southwood, 1974;Chen and Hasegawa, 1974;Waters et al, 1995), which takes energy from the coupling with the magnetospheric compressional mode. The evaluation of the spectral ratio G (or gain factor) and the phase difference between the H components at two adjacent stations can be used as an additional method to investigate this possibility (Baransky et al, 1985;Waters et al, 1991;Menk et al, 2000).…”

Section: Resultsmentioning

confidence: 99%

“…The evaluation of the spectral ratio G (or gain factor) and the phase difference between the H components at two adjacent stations can be used as an additional method to investigate this possibility (Baransky et al, 1985;Waters et al, 1991;Menk et al, 2000). In general, this method requires that the spatial separation between the stations should be small enough to maintain adequate coherence in the wave fields (Waters et al, 1995), but also large enough to resolve the variation of the phase difference; in our study, the separations between pairs of adjacent stations (from 3 • to 8 • , and in particular, 7 • for the couple NUR-SOD) are larger than in the study by Waters et al (1995); however, Menk et al (1999), using station pairs spaced up to ∼6 • , have shown that, for some events, resonance signatures can also be obtained for the most widely spaced station pairs. In Fig.…”

Section: Resultsmentioning

confidence: 99%

Geomagnetic field fluctuations during the passage at the Earth’s orbit of the tail of the 15–16 July 2000 ejecta

2002

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Abstract. In this work we present the analysis of the geomagnetic field fluctuations observed at different ground stations (approximately along two latitudinal arrays, separated by several hours in local time) during the passage at the Earth's orbit of the tail of the 15-16 July 2000 coronal ejecta. The time interval of interest is characterized by northward interplanetary magnetic field conditions and several changes in the solar wind dynamic pressure. We found at all stations, both in the local morning and in the local evening, simultaneous and highly coherent waves at the same discrete frequencies (∼1.8 and ∼3.6 mHz) and suggest a possible interpretation in terms of global compressional modes driven by an impulsive variation of the solar wind pressure. Along the array situated in the morning sector, at the highest latitudes, the higher frequency mode seems to couple with the local field line resonance; on the other hand, along the array situated in the evening sector, the characteristics of the observed fluctuations suggest that the highest latitude station could be located at the footprint of open field lines. Our results also show that solar wind pressure variations observed during the recovery phase of the storm do not find correspondence in the geomagnetic field variations, regardless of local time and latitude; conversely, some hours later continuous solar wind pressure variations find a close correspondence in the geomagnetic field variations at all stations.

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The temporal variation of the frequency of high latitude field line resonances

Cited by 78 publications

References 25 publications

Coordinated ISTP satellite and ground observations of morningside Pc5 waves

Coordinated ISTP satellite and ground observations of morningside Pc5 waves

Comparison of equatorial plasma mass densities deduced from field line resonances observed at ground for dipole and IGRF models

Geomagnetic field fluctuations during the passage at the Earth’s orbit of the tail of the 15–16 July 2000 ejecta

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