Statistical study of hydromagnetic chorus events at very high latitudes

Anderson, H. M.; Engebretson, M. J.; Arnoldy, R. L.; Cahill, L. J.; Newell, P. T.

doi:10.1029/94ja02151

Cited by 6 publications

(6 citation statements)

References 23 publications

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“…Popecki et al [1993] reported the same observation, from which they concluded that there was no solar effect on Pc 1-2 ground observations. The local time variations shown here are consistent with those observed in HM chorus events by Anderson et al [1995], and as in that study we suggest they may be caused by the offset between the magnetic and geographic poles, which may cause longitude-dependent effects.…”

Section: Statistical Studysupporting

confidence: 91%

Ground observations and possible source regions of two types of Pc 1‐2 micropulsations at very high latitudes

Dyrud¹,

Engebretson²,

Posch³

et al. 1997

J. Geophys. Res.

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Abstract. We have used 1-year's data from the recently installed Magnetometer Array for Cusp and Cleft Studies (MACCS) in Arctic Canada and from two stations of the developing "conjugate" array of Automated Geophysical Observatories (AGOs) in Antarctica to study ULF waves in the Pc 1-2 (100-600 mHz) frequency band at cusp and polar cap latitudes (A -• 74* -80*). In this paper we focus on the spectral properties and latitudinal and local time distributions of Pc 1-2 events observed during 1994 and use these along with several case studies to infer the source locations of the two major wave types we have observed. We found little variation in center-band frequency of the Pc 1-2 waves we observed, but the average event bandwidth was distinctly wider at stations near 80* MLAT than at stations near 75* MLAT. Broadband waves, with diffuse spectral character, dominated at the higher latitudes, but their occurrence was confined at most stations to within 4 hours of local magnetic noon. Waves with narrower bandwidth were much more common in our data set, and were the statistically dominant wave type at the lower-latitude MACCS stations. Their occurrence was also limited to the dayside but extended both later and more widely in local time than the more broadband waves. These multistation observations, combined with data from the DMSP, IMP 8, and Geotail satellites, suggest the possibility that these two wave types originate in quite different regions near the magnetospheric boundary; the more narrowband waves in the subsolar and postnoon equatorial region, and the more broadband waves in the high-latitude plasma mantle (and possibly at the poleward edge of the cusp). The cusp itself appears to not be a significant source of Pc 1-2 wave activity that can be detected by ground observatories.

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Section: Statistical Studysupporting

confidence: 91%

Ground observations and possible source regions of two types of Pc 1‐2 micropulsations at very high latitudes

Dyrud¹,

Engebretson²,

Posch³

et al. 1997

J. Geophys. Res.

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“…Omura et al [2010] theoretically showed that these EMIC waves with high-frequency sweep rate (e.g., 30 s/Hz in Pickett et al [2010]) are EMIC-triggered emissions caused by nonlinear frequency variations from the linear EMIC waves (the triggering EMIC waves) and the gradient of the background magnetic field near the magnetic equator. Similar rising tone structures have been observed on the ground, for example, as hydromagnetic emissions or hydromagnetic chorus [e.g., Fukunishi et al, 1981;Anderson et al, 1995], but timescales of those emissions (∼200-600 s) are much longer than those of EMIC-triggered emissions (several tens of seconds). The EMIC waves scatter magnetospheric protons, and those protons precipitate into the ionosphere to cause the proton 10.1002/2015JA021681 aurora [e.g., Yahnin et al, 2007;Sakaguchi et al, 2008;Nomura et al, 2012].…”

Section: Introductionmentioning

confidence: 52%

Pulsating proton aurora caused by rising tone Pc1 waves

Nomura

Shiokawa

Omura³

et al. 2016

JGR Space Physics

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We found rising tone emissions with a dispersion of ∼1 Hz per several tens of seconds in the dynamic spectrum of a Pc1 geomagnetic pulsation (Pc1) observed on the ground. These Pc1 rising tones were successively observed over ∼30 min from 0250 UT on 14 October 2006 by an induction magnetometer at Athabasca, Canada (54.7°N, 246.7°E, magnetic latitude 61.7°N). Simultaneously, a Time History of Events and Macroscale Interactions during Substorms panchromatic (THEMIS) all‐sky camera detected pulsations of an isolated proton aurora with a period of several tens of seconds, ∼10% variations in intensity, and fine structures of 3° in magnetic longitudes. The pulsations of the proton aurora close to the zenith of ATH have one‐to‐one correspondences with the Pc1 rising tones. This suggests that these rising tones scatter magnetospheric protons intermittently at the equatorial region. The radial motion of the magnetospheric source, of which the isolated proton aurora is a projection, can explain the central frequency increase of Pc1, but not the shorter period (tens of seconds) frequency increase of ∼1 Hz in Pc1 rising tones. We suggest that EMIC‐triggered emissions generate the frequency increase of Pc1 rising tones on the ground and that they also cause the Pc1 pearl structure, which has a similar characteristic time.

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“…The predominant high‐latitude (L = 6–8) ground ULF signal near local noon is quasi‐structured hydromagnetic chorus/emissions [ Fukunishi et al , 1981; Menk et al , 1993; Anderson et al , 1995]. Since the early 1960s, it has been noted that the ULF waves on the ground near local noon were either turned on or enhanced in association with sudden impulses in the Earth's magnetic field [ Troitskaya , 1961; Heacock and Hessler , 1965; Kokubun and Oguti , 1968; Troitskaya et al , 1968; Hirasawa , 1981].…”

Section: Introductionmentioning

confidence: 99%

Pc 1 waves and associated unstable distributions of magnetospheric protons observed during a solar wind pressure pulse

et al. 2005

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[1] We present observations of Pc 1 waves ($0.6 Hz) that occurred shortly after a strong (>20 nPa) compression of Earth's magnetosphere at 1321 UT, 18 March 2002. Intense Pc 1 waves were observed at several high-latitude ground stations in Antarctica and Greenland from 1321 UT to beyond 1445 UT. Two wave bursts were recorded at the Polar satellite at 1338 and 1343-1344 UT as it passed outbound in the Southern Hemisphere at 1154 local time (SM magnetic latitude of À22°and near L = 7.5) in good magnetic conjunction with the Antarctic. The pressure increase created a significant population of protons between a few hundred eV and several keV, whose fluxes were mostly perpendicular to B. These protons seem to have replaced the quiescent stream of protons (presumably convected from the plasma sheet) that existed before this increase. There was also a nearly two-order-of-magnitude increase in the population of thermal/suprathermal (0.32-410 eV) protons. The generation of ion cyclotron waves is expected to limit the proton temperature anisotropy A, defined as T ? /T k À 1. The ion cyclotron instability driven by the observed hot ion temperature anisotropy is studied using two models, with and without the presence of cold background plasma. Peaks in the calculated instability as a function of time show excellent agreement with the times of the Polar wave bursts, which were measured a few tens of seconds after maxima in the instability calculation. The time delay is consistent with the propagation time to the spacecraft from a source nearer to the equatorial plane. The hot proton population at Polar appears to be driven back to stability by a sudden increase in very field-aligned protons having energies less than the hot perpendicular population, suggesting a different source for the two populations. These observations confirm the importance of both the energization and/or increase in population of protons transverse to B in the several keV range (possibly betatron acceleration as a result of the pressure pulse), and the presence of greatly increased fluxes of lower energy protons (100s of eV to a few keV), predominantly aligned along B, in determining whether the particle population is unstable at a given time.Citation: Arnoldy, R. L., et al. (2005), Pc 1 waves and associated unstable distributions of magnetospheric protons observed during a solar wind pressure pulse,

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Statistical study of hydromagnetic chorus events at very high latitudes

Cited by 6 publications

References 23 publications

Ground observations and possible source regions of two types of Pc 1‐2 micropulsations at very high latitudes

Ground observations and possible source regions of two types of Pc 1‐2 micropulsations at very high latitudes

Pulsating proton aurora caused by rising tone Pc1 waves

Pc 1 waves and associated unstable distributions of magnetospheric protons observed during a solar wind pressure pulse

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