On the statistical relation between ion upflow and naturally enhanced ion-acoustic lines observed with the EISCAT Svalbard radar

Ogawa, Y.; Buchert, Stephan; Häggström, Ingemar; Rietveld, M. T.; Fujii, Ryoichi; Nozawa, Satonori; Miyaoka, Hiroshi

doi:10.1029/2010ja015827

Cited by 20 publications

(26 citation statements)

References 40 publications

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“…At high latitudes the spectral power in the ion acoustic regime is occasionally enhanced above the thermal backscatter. These so-called naturally enhanced ion acoustic lines (NEIAL) occur in the altitude range of 140 to 1900 km during magnetically disturbed conditions (Foster et al, 1988;Rietveld et al, 1991;Sedgemore-Schulthess and St. Maurice, 2001;Ogawa et al, 2006Ogawa et al, , 2011. The enhancements observed during NEIALs can be up to 4-5 orders of magnitude and are typically extended over hundreds of kilometers in altitude.…”

Section: Introductionmentioning

confidence: 99%

Enhanced EISCAT UHF backscatter during high-energy auroral electron precipitation

et al. 2013

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Abstract. Natural enhancements in the backscattered power of incoherent scatter radars up to 5 orders of magnitudes above the thermal backscatter are sometimes observed at high latitudes. Recently observations of enhancements in the backscattered power including a feature at zero Doppler shift have been reported. These enhancements are limited in altitude to tens of kilometers. The zero Doppler shift feature has been interpreted as a signature of electron density cavitation. Enhanced plasma lines during these observations have also been reported. We report on the first EISCAT UHF observations of enhanced backscattered radar power including a zero Doppler shift feature. The enhancements originated from two distinct and intermittent layers at about 200 km altitude. The altitude extent of the enhancements, observed during auroral high-energy electron precipitation, was < 2 km.

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Section: Introductionmentioning

confidence: 99%

Enhanced EISCAT UHF backscatter during high-energy auroral electron precipitation

et al. 2013

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“…NEIALs are observed as enhancement of ion line shoulders over a wide altitude range (several hundred kilometres), with several order-of-magnitude increases of one or both ion line shoulders -and no features with a zero Doppler shift. While NEIALs have been found to be related to soft precipitation, both statistically (Ogawa et al, 2011) and on an event basis (e.g. Sullivan et al, 2008), the SLT-like anomalous echoes in this study were found to be closely related to energetic precipitation, characteristic of discrete aurora.…”

Section: Discussionmentioning

confidence: 81%

Relation of anomalous F region radar echoes in the high-latitude ionosphere to auroral precipitation

Dahlgren¹,

Schlatter²,

Ivchenko³

et al. 2017

Ann. Geophys.

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Abstract. Non-thermal echoes in incoherent scatter radar observations are occasionally seen in the high-latitude ionosphere. Such anomalous echoes are a manifestation of plasma instabilities on spatial scales matching the radar wavelength. Here we investigate the occurrence of a class of spatially localized anomalous echoes with an enhanced zero Doppler frequency feature and their relation to auroral particle precipitation. The ionization profile of the E region is used to parametrize the precipitation, with nmE and hmE being the E region peak electron density and the altitude of the peak, respectively. We find the occurrence rate of the echoes to generally increase with nmE and decrease with hmE, thereby indicating a correlation between the echoes and high-energy flux precipitation of particles with a high characteristic energy. The highest occurrence rate of > 20 % is found for hmE = 109 km and nmE = 10 11.9 m −3 , averaged over the radar observation volume.

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“…However, these observations refer to a case without electron plasma wave activity. In studies of ion upflow and naturally enhanced ion lines, 58 it was found that NEIALs were found predominantly at enhanced electron-ion temperature ratios. Under these conditions it is possible that ion and electron holes can have a more important role than in our simulations.…”

Section: Discussionmentioning

confidence: 99%

“…It is possible that the enhanced temperature ratios T e =T i ! 2 observed in some experiments 58 will allow longlived ion phase-space vortices.…”

Section: Discussionmentioning

confidence: 99%

Nonlinear beam generated plasma waves as a source for enhanced plasma and ion acoustic lines

et al. 2011

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Observations by, for instance, the EISCAT Svalbard Radar (ESR) demonstrate that the symmetry of the naturally occurring ion line in the polar ionosphere can be broken by an enhanced, nonthermal, level of fluctuations (naturally enhanced ion-acoustic lines, NEIALs). It was in many cases found that the entire ion spectrum can be distorted, also with the appearance of a third line, corresponding to a propagation velocity significantly slower than the ion acoustic sound speed. It has been argued that selective decay of beam excited primary Langmuir waves can explain some phenomena similar to those observed. We consider a related model, suggesting that a primary nonlinear process can be an oscillating two-stream instability, generating a forced low frequency mode that does not obey any ion sound dispersion relation. At later times, the decay of Langmuir waves can give rise also to enhanced asymmetric ion lines. The analysis is based on numerical results, where the initial Langmuir waves are excited by a cold dilute electron beam. By this numerical approach, we can detect fine details of the physical processes, in particular, demonstrate a strong space-time intermittency of the electron waves in agreement with observations. Our code solves the full Vlasov equation for electrons and ions, with the dynamics coupled through the electrostatic field derived from Poisson's equation. The analysis distinguishes the dynamics of the background and beam electrons. This distinction simplifies the analysis for the formulation of the weakly nonlinear analytical model for the oscillating two-stream instability. The results have general applications beyond their relevance for the ionospheric observations.

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On the statistical relation between ion upflow and naturally enhanced ion-acoustic lines observed with the EISCAT Svalbard radar

Cited by 20 publications

References 40 publications

Enhanced EISCAT UHF backscatter during high-energy auroral electron precipitation

Enhanced EISCAT UHF backscatter during high-energy auroral electron precipitation

Relation of anomalous F region radar echoes in the high-latitude ionosphere to auroral precipitation

Nonlinear beam generated plasma waves as a source for enhanced plasma and ion acoustic lines

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