Parallel electric fields inferred during a pulsating aurora

Williams, John; MacDonald, E.; McCarthy, Michael; Peticolas, L. M.; Parks, G. K.

doi:10.5194/angeo-24-1829-2006

Cited by 8 publications

(11 citation statements)

References 18 publications

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“…For the case of 18 eV, the radar sees . These parameters are well within the ranges known to occur in the auroral ionosphere [21]. The peak value of each spectrum is given at the top right of each panel.…”

supporting

confidence: 67%

Cavitating Langmuir Turbulence in the Terrestrial Aurora

et al. 2012

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Langmuir cavitons have been artificially produced in the earth's ionosphere, but evidence of naturally-occurring cavitation has been elusive. By measuring and modeling the spectra of electrostatic plasma modes, we show that natural cavitating, or strong, Langmuir turbulence does occur in the ionosphere, via a process in which a beam of auroral electrons drives Langmuir waves, which in turn produce cascading Langmuir and ion-acoustic excitations and cavitating Langmuir turbulence. The data presented here are the first direct evidence of cavitating Langmuir turbulence occurring naturally in any space or astrophysical plasma.PACS numbers: 94.05. Lk, 94.05.Pt, 94.05.Fg, 94.20.wj Langmuir turbulence is known to occur in controlled laboratory [1,2] and space plasma experiments [3][4][5] and is thought to occur naturally in a variety of space and astrophysical plasmas, including pulsar magnetospheres [6], the solar corona [7], the interplanetary medium [8], planetary foreshocks [9], the terrestrial magnetosphere [10], and the ionosphere [11][12][13]. In its most developed form, this turbulence contains electron Langmuir modes trapped in dynamic density depressions known as cavitons [14][15][16]. Cavitons have been shown to be artificially produced in the earth's ionosphere during high-power radiowave pumping experiments as deduced from radar spectra containing simultaneously-excited up and downshifted Langmuir and ion-acoustic lines plus a central peak due to cavitation [3][4][5], but evidence of naturally occurring cavitation has until now been elusive.Between 18 and 21 UT on 11 and 12 November 1999 a measurement program designed to detect both ionacoustic and Langmuir modes was run on the European Incoherent Scatter Scientific Association (EISCAT) 224-MHz radar located near Tromsø in northern Norway (local standard time in Norway is UT plus one hour). The principal objectives were to observe enhanced waves stimulated by high-power radiowave pumping, and, in the event of auroral activity, to gather data on natural energetic waves [17]. On both nights conditions were disturbed, and enhanced echoes were detected, the strongest being on 11 November between 18:18:30 and 18:21:30 UT, during the passage of an aurora through the vertically-directed radar beam. Fig. 1 presents parameters derived from the ion-acoustic backscatter between 18:15 and 18:28 UT, during the most intense auroral event. Fig. 2 shows the intensities of Langmuir and ion-acoustic backscatter as a function of height and time. The prominent features occurring between 18:18:30 and 18:20:30 UT and at 18:23:30 UT near 300 and 250 km altitude, respectively, are backscatter associated with the aurora, and are the most energetic natural events observed on either night. Two other events occurred later that evening and two more on the following evening. Weak ion-acoustic enhancements occurred during each event; the Langmuir enhancements, however, are always stronger. Fig. 3 shows up and down-shifted spectral lines, or "shoulders", which are produced by Doppler-...

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supporting

confidence: 67%

Cavitating Langmuir Turbulence in the Terrestrial Aurora

et al. 2012

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“…7) taken during the PFISR data interval, and within the field-of-view of the Poker Flat ASC, show this to be a downgoing population and therefore primary precipitation, or perhaps secondary electrons from the conjugate hemisphere (Sato et al, 2002(Sato et al, , 2004 or downward accelerated secondary electrons such as those observed by Williams et al (2006). Fig.…”

Section: Article In Pressmentioning

confidence: 92%

“…It is generally believed that pulsating aurora is caused by energetic electrons (Smith et al, 1980;McEwen et al, 1981) precipitated by pitch-angle diffusion in the vicinity of the equatorial region of the magnetosphere Davidson, 1986a, b;Huang et al, 1990), a result based on velocity dispersion analyzes of sounding rocket observations of energetic electrons in conjunction with pulsating aurora. However, note that a lack of velocity dispersion in the energetic particle measurements has been shown in some instances (Johnstone, 1971;Williams et al, 2006).…”

Section: Introductionmentioning

confidence: 94%

PFISR and ROPA observations of pulsating aurora

Jones

Lessard

Fernandes

et al. 2009

Journal of Atmospheric and Solar-Terrestrial Physics

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“…Such a complexity is not unexpected. The downgoing low-energy electrons observed by LEO satellites may owe their origin to a number of sources: (a) the low-energy portion of the CPS primary electron precipitation; (b) secondary electrons excited by primary electron precipitation, which subsequently enter the LEO satellite observation as downgoing fluxes via a variety of mechanisms [e.g., Evans, 1974;Evans et al, 1987;Williams et al, 2006]. The secondary electrons can be excited by primary electron precipitation corresponding to pulsating auroras, ambient diffuse auroras, or discrete auroras.…”

Section: On the Low-energy Electron Signature Associated With Papmentioning

confidence: 99%

Low‐energy ion precipitation structures associated with pulsating auroral patches

et al. 2015

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Pulsating auroras often appear in forms of geo‐stable or slowly convecting “patches.” These patches can maintain their rough shape and size over many sequences of luminosity pulsations, yet they slowly drift with ionospheric E × B convection. Because of these characteristics, there has long been a speculation that the pulsating auroral patch (PAP) is connected to flux tubes filled with enhanced cold plasma. In this study, we perform a survey on pulsating auroral events when the footprints of low‐Earth‐orbit satellites traversed the PAPs, with a focus on the low‐energy particle signatures associated with the PAPs. As a result, we identified, in a majority (~2/3) of events, the existence of a low‐energy ion precipitation structure that is collocated with the PAP, with core energies ranging from several tens of eV up to a few hundred eV. This result supports the hypothesis that a PAP connects to flux tubes filled with enhanced cold plasma. We further propose that the plasma outflows from the ionosphere are the origin of such cold plasma flux tubes. We suggest that the PAP is formed by a combination of high‐energy electrons of a magnetospheric origin, the low‐energy plasma structure of an ionospheric origin, and certain ELF/VLF waves that are intensified and modulated in interactions with both the hot and cold plasma populations.

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Parallel electric fields inferred during a pulsating aurora

Cited by 8 publications

References 18 publications

Cavitating Langmuir Turbulence in the Terrestrial Aurora

Cavitating Langmuir Turbulence in the Terrestrial Aurora

PFISR and ROPA observations of pulsating aurora

Low‐energy ion precipitation structures associated with pulsating auroral patches

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