Non-thermal ionospheric plasma studies using the incoherent scatter technique

Kofman, W.; St.-Maurice, J.-P.

doi:10.1016/0021-9169(95)00127-1

Cited by 4 publications

(1 citation statement)

References 47 publications

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“…Clearly this condition does not apply under conditions of strong plasma turbulence, when a non‐Maxwellian velocity distribution gives rise to a “distorted” ion acoustic spectrum. Non‐Maxwellian plasmas can arise naturally, for example due to ion neutral collisions under the influence of strong electric fields or during auroral processes where beam‐driven instabilities cause natural Langmuir turbulence that enhances the ion acoustic waves to which the radar is sensitive [see, e.g., Kofman and St.‐Maurice , 1996; Forme and Fontaine , 1999].…”

Section: Introductionmentioning

confidence: 99%

A method for improving plasma temperature estimates from incoherent scatter analysis during artificial ionospheric modification experiments

2010

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[1] Spectral features in incoherent scatter data, such as those caused by the purely growing mode (PGM), can often be strongly enhanced during the first few seconds of artificial ionospheric heating experiments, such as those carried out using the high-power European Incoherent Scatter HF heater at Tromsø. These features, often referred to as "overshoot" effects, are indicators of turbulent non-Maxwellian plasma, and the analysis of these spectra using standard incoherent scatter data analysis software leads to a poor estimation of the plasma parameters (particularly electron and ion temperature) during RF heating experiments. In this study, a procedure is developed to derive a more reliable estimate of plasma temperature during periods when the incoherent scatter spectrum is affected by contamination from the PGM. This is achieved by removing the PGM from the measured spectrum and then analyzing the modified spectrum using standard software. The results are compared to those obtained from the analysis of the original, contaminated spectra. It is found that the differences between the results obtained from the corrected and uncorrected spectra are strongly proportional to the magnitude of the PGM feature. We also show that the bulk temperatures during the remainder of the "heater on" period after the overshoot can generally be estimated reliably by the standard analysis software, though with some important exceptions. These results are important since the plasma temperatures play a crucial role in governing thermal conduction processes, and their correct estimation is thus very important to understanding the underlying physical processes which occur during ionospheric heating.

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Section: Introductionmentioning

confidence: 99%

A method for improving plasma temperature estimates from incoherent scatter analysis during artificial ionospheric modification experiments

2010

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Parametric decay of beam-driven Langmuir wave and enhanced ion-acoustic fluctuations in the ionosphere: a weak turbulence approach

Forme¹

1999

Ann. Geophys.

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Abstract. We present a model that describes the decay of beam generated Langmuir waves into ion-acoustic waves in the topside ionosphere. This calculation is done within the frame of the weak turbulence approximation. We study the spectral signature of such a process as seen by a VHF incoherent scatter radar. An incoherent scatter (IS) spectrum is characterized by two maxima at k r d r and Àk r d r , the right and left ion lines respectively. It is shown that, for reasonable beam parameters, the parametric decay of beam-generated Langmuir waves can enhance either the right, the left or both ion lines simultaneously. The shape of the spectrum can change drastically on time scale of about 0.1 to 1 s. The role of the beam parameter as well as the ionospheric parameters is also investigated. For a given beam number density, the beam energy or the background density are important to trigger either the left or the right ion line. A large energy spread of the beam or low electron collision frequencies can explain the simultaneous observations of the left and the right ion line. The importance of the electron collision frequency can explain the altitude distribution of the coherent echoes observed by incoherent scatter radars.

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Naturally enhanced ion acoustic fluctuations seen at different wavelengths

Forme¹,

Ogawa²,

Buchert³

2001

J. Geophys. Res.

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Abstract. We present European Incoherent Scatter (EISCAT) Svalbard Radar observations of enhanced incoherent scatter ion-acoustic spectra with transmitted frequencies slightly shifted relative to the radar central frequency. This study confirms the initial findings that (1) the nat•xrally enhanced ion acoustic lines sometimes show asymmetric power profiles and (2) the amplitude enhancement of upgoing and downgoing ion-acoustic waves occurs at somewhat different altitudes and different power levels. These observational facts are modeled using the parametric decay of beam driven Langmuir wave in an inhomogeneous medium. It is shown that the density gradient with altitude as well as the collisions contribute to an altitude variation of ion-acoustic spectra and may account for the observed signatures. It is also responsible for the transition from upshifted to downshifted enhanced ion lines. Our model shows that the power radiated by enhanced spectra varies with the wavelength and that the power difference between two wavelengths varies with altitude.

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Non-thermal ionospheric plasma studies using the incoherent scatter technique

Cited by 4 publications

References 47 publications

A method for improving plasma temperature estimates from incoherent scatter analysis during artificial ionospheric modification experiments

A method for improving plasma temperature estimates from incoherent scatter analysis during artificial ionospheric modification experiments

Parametric decay of beam-driven Langmuir wave and enhanced ion-acoustic fluctuations in the ionosphere: a weak turbulence approach

Naturally enhanced ion acoustic fluctuations seen at different wavelengths

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