Scattering of electromagnetic waves from a plasma: Enhanced ion acoustic fluctuations due to ion‐ion two‐stream instabilities

Wahlund, Jan‐Erik; Forme, F.; Opgenoorth, H. J.; Persson, Moa; Mishin, E. V.; Volokitin, A. S.

doi:10.1029/92gl02101

Cited by 62 publications

(53 citation statements)

References 16 publications

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“…This questions the idea that two enhanced shoulders ever coexist on one magnetic field line and deals therefore with the objection of Wahlund et al [1992a] to electron ionacoustic instabilities being the cause of the enhanced radar spectra. Two-stream instabilities do not require the very high current densities needed to explain the spectra in terms of electron ion-acoustic instabilities, but they do require that the ion drift velocity be of the order of its thermal velocity.…”

Section: Observationsmentioning

confidence: 99%

“…St.-Maurice et al [ 1996] discuss the inferred field-aligned currents in terms of intense parallel electric fields of up to a few hundred microvolts per meter in magnitude together with horizontal scales of a few hundred meters or less. Forme [1993] has suggested that ion-acoustic fluctuations may be due to parametric decay of Langmuir waves, and Wahlund et al [1992a] propose a theory based on ion-ion two-stream instabilities. Foster et al [1988] using the Millstone Hill 440-MHz radar at angles of at least 11 ø away from the local magnetic field direction revealed echoes that could easily have been mistaken for satellite passes had they not had a consistent altitude profile and come from a fixed region of space.…”

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confidence: 99%

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Coherent EISCAT Svalbard Radar spectra from the dayside cusp/cleft and their implications for transient field‐aligned currents

Sedgemore-Schulthess¹,

Lockwood²,

Trondsen³

et al. 1999

J. Geophys. Res.

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Abstract. Naturally enhanced incoherent scatter spectra from the vicinity of the dayside cusp/cleft, interpreted as being due to plasma turbulence driven by short bursts of intense field-aligned current, are compared with high-resolution narrow-angle auroral images and meridian scanning photometer data. Enhanced spectra have been observed on many occasions in association with nightside aurora, but there has been only one report of such spectra seen in the cusp/cleft region. Narrow-angle images show considerable change in the aurora on timescales shorter than the 10-s radar integration period, which could explain spectra observed with both ion lines simultaneously enhanced. Enhanced radar spectra are generally seen inside or beside regions of 630-nm auroral emission, indicative of sharp F region conductivity gradients, but there appears also to be a correlation with dynamic, small-scale auroral forms of order 100 rn and less in width.

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Section: Observationsmentioning

confidence: 99%

mentioning

confidence: 99%

Coherent EISCAT Svalbard Radar spectra from the dayside cusp/cleft and their implications for transient field‐aligned currents

Sedgemore-Schulthess¹,

Lockwood²,

Trondsen³

et al. 1999

J. Geophys. Res.

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show abstract

“…Rietveld et al (1991) presented a systematic study of NEIALs received by the EISCAT UHF system. Several models to explain NEIALs have been proposed such as the current driven instability (Foster et al, 1988) and the ion-ion twostream instability (Wahlund et al, 1992). To decide whether and how the cross section of NEIALs depends on the wave vector k may enable us to distinguish between such instabilities.…”

Section: Introductionmentioning

confidence: 99%

Frequency dependent power fluctuations: a feature of the ESR system or physical?

2000

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Abstract. The k-dependence of the received power in high signal-to-noise ratio (SNR) conditions, occurring for naturally enhanced ion-acoustic lines (NEIALs) and for real satellites, is investigated by using the EISCAT Svalbard Radar (ESR), where the data are recorded in eight separate channels using di erent frequencies. For the real satellites we ®nd large variations of the relative powers from event to event, which is probably due to a di erent number of pulses catching the satellite over the integration period. However, the large power di erence remains unexpected in one case. Over short time scale ( 10 s) the relative power di erence seems to be highly stable. For most NEIAL events the di erences between channels are within noise level. In a few cases variations of the relative power well above both the estimated and expected 1-sigma level occur over a signal preintegrated pro®le. We thus suggest that the frequency dependence of the power in NEIAL events has its origin in the scattering medium itself as the most plausible explanation.

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Section: Introductionmentioning

confidence: 99%

Frequency dependent power fluctuations: a feature of the ESR system or physical?

Ogawa

Forme

Buchert

2000

Annales Geophysicae

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Abstract. The k-dependence of the received power in high signal-to-noise ratio (SNR) conditions, occurring for naturally enhanced ion-acoustic lines (NEIALs) and for real satellites, is investigated by using the EISCAT Svalbard Radar (ESR), where the data are recorded in eight separate channels using dierent frequencies. For the real satellites we ®nd large variations of the relative powers from event to event, which is probably due to a dierent number of pulses catching the satellite over the integration period. However, the large power dierence remains unexpected in one case. Over short time scale ( 10 s) the relative power dierence seems to be highly stable. For most NEIAL events the dierences between channels are within noise level. In a few cases variations of the relative power well above both the estimated and expected 1-sigma level occur over a signal preintegrated pro®le. We thus suggest that the frequency dependence of the power in NEIAL events has its origin in the scattering medium itself as the most plausible explanation.

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Scattering of electromagnetic waves from a plasma: Enhanced ion acoustic fluctuations due to ion‐ion two‐stream instabilities

Cited by 62 publications

References 16 publications

Coherent EISCAT Svalbard Radar spectra from the dayside cusp/cleft and their implications for transient field‐aligned currents

Coherent EISCAT Svalbard Radar spectra from the dayside cusp/cleft and their implications for transient field‐aligned currents

Frequency dependent power fluctuations: a feature of the ESR system or physical?

Frequency dependent power fluctuations: a feature of the ESR system or physical?

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