Spectral features of lightning-induced ion cyclotron waves at low latitudes: DEMETER observations and simulation

International audience[1] We use a comprehensive analysis of 6-component ELF wave data from the DEMETER satellite to study proton whistlers, placing emphasis on low-latitude events originating from lightning strokes in the hemisphere opposite to the hemisphere of observation. In this case, the formation of proton whistlers does not involve mode conversion caused by a strong mode coupling at a crossover frequency, although a polarization reversal remains an important element in formation of the phenomenon. DEMETER measurements of the six electromagnetic field components in the frequency band below 1000 Hz make it possible to determine not only the dynamic spectrum, but also the wave polarization, the wave normal angle, and the normalized parallel component of the Poynting vector. This permits us to address fine features of proton whistlers, in particular, we show that the deviation of the upper cutoff frequency from the equatorial cyclotron frequency is related to the Doppler shift. Experimental study of proton whistlers is supplemented by an investigation of ion cyclotron wave propagation in a multicomponent magnetoplasma and by numerical modeling of spectrograms, both in the frame of geometrical optics

On the boundary layer between a flowing plasma and a magnetic field. Part I : The conditions for equilibrium

A qualitative study is made of a plane charge-neutral magnetopause separating a field-free plasma from a plasma-free magnetic field, in the case where the plasma is flowing parallel to the applied field. It is shown that the existence of small-scale equilibrium dépends on boundary conditions which are governed by the large-scale structure of the System. On certain conditions, which are defined, equilibrium is possible at ail flow speeds. For a class of structures characterized by approximately axial flow, these conditions cannot be satisfied if the plasma encloses the magnetic field, but can if the magnetic field encloses the plasma. They are satisfied most naturally if, in addition, the magnetopause has the form of a torus. While intended originally as a contribution to magnetospheric physics, this study may be more relevant to the high-0 confinement of fusion plasmas

The analysis of 6-component measurements of a random electromagnetic wave field in a magnetoplasma. Part. 2 : Model identification

A method is proposed for the analysis of measurements of the six components of a random electromagnetic wave fields. This field, observed at a fixed point in a magnetoplasma, is assumed to be a Gaussian stationary and ergodic wide-band process. It is described statistically by the distribution of wave energy density with respect to the variables frequency and wave-normal direction. A parametric model of the wave distribution function is assumed. Using the principle of maximum likelihood, a method is developed for estimating the unknown parameters from data consisting of continuous measurements of the six field components over a finite time interval. The accuracy of the estimated parameters is evaluated. Finally, methods are proposed for testing the validity of the model, and for comparing the relative merits of different possible models when more than one exist

The analysis of 6-component measurements of a random electromagnetic wave field in a magnetoplasma. I : The direct problem

This is the first of a series of papers, the general subject of which is how to interpret a set of simultaneous measu- rements of the three electric and three magnetic components of a random electromagnetic wave field in a magnetoplasma. The point at which the measurements are made is assumed to be stationary with respect to the plasma. In this first paper, the following problems are treated : how to define, within the framework of classical electrodynamics, a distribution function that characterizes the statistics of a linear random electromagnetic wave field in a lossless magnetoplasma the direct problem of predicting the statistical properties of measurements of the six components of a field of this type, when the distribution function is known

Diagnostic de plasmas hors d'équilibre au moyen de mesures du microchamp aléatoire

Dans le présent rapport, on rend compte des travaux scientifiques effectués, dans le cadre de l'Action Thématique Programmée "Internationale 1974", au titre de la Décision n° 9201. Le sujet de ces travaux est le diagnostic de plasmas hors d'équilibre au moyen de mesures du microchamp aléatoire. Ils font partie d'un programme de recherches dont le but ultime est de mettre au point un nouvel instrument de mesure de la fonction de distribution des vitesses des électrons dans un plasma non-Maxwellien du type de celui qui existe dans l'ionosphère

Project porcupine : the MF mutual-impedance probe experiment. Part I : Flight F2 (March 1977)

Results are presented from a medium-frequency (0.1 - 1.5 MHz) mutual-impedance probe flown on the three rockets in the auroral ionosphere. The main purpose of these experiments was to measure the field-aligned drift velocity of the thermal electrons, from the resulting non-reciprocal frequency- shift of the lower oblique resonance. In the first experiment (Porcupine F2), the data exhibited frequency-shifts much larger than expected, and which varied cyclically as the payload spun. These spurious shifts, which were partly of technological origin, masked any shifts due to field-aligned drift. They led to a redesign of the probe. In the second experiment (Porcupine F3), the data were consistent with downward electron drifts, but their apparent high velocity casts doubt on this interpretation. The data from the third experiment (Porcupine F4) exhibited frequency-shifts that clearly were related to the cross-field drift of the plasma under the influence of the perpendicular component of the auroral electric field, but again they were larger than the values expected theoretically. The conclusions are that this method for measu- ring field-aligned electron drift velocity is not yet ready for scientific use, but that it would become useful if its sensitivity could be improved by an order of magnitude. Suggestions are made as to how this improvement might be achieved

Project porcupine : the MF mutual-impedance probe experiment. Part II : Flight F3 and F4 (March 1979)

This is the second part of a report on the results from the medium-frequency (MF) mutual-impedance probe experiment that was supplied by the Centre for Research in Environmental Physics (CRPE, Orléans, France) as a contribution to the West-German Porcupine program of research on auroral physics during the International Magnetospheric Study. The subject of Part 1 was the results from the first successful flight, named F2, which took place from ESRANGE (Kiruna, Sweden) on 20 March 1977. On that occasion, the MF probe experiment did not succeed in its objective of detecting field-aligned drift motion of the thermal electrons in the auroral ionosphere. The non-reciprocal shift of the lower oblique resonance (L.O.R.) frequency that this motion should have produced was masked by a similar but much larger shift that was obviously spurious, since it varied, more or less sinusoidally, as a function of the spin-phase angle. Various conceivable physical causes for this spurious shift were studied, but were rejected. The question of whether the true cause was some other physical phenomenon, as yet unidentified, or whether it was technological in nature, had to be left open. The results from the flight F2 nevertheless suggested a number of ways in which the experiment could be improved, and these were discussed in Section 5, which concluded Part 1 of the report. In Part 2, after the present preface, Section 7 describes how these and other modifications were made to the MF probe, in preparation for the flights F3 and F4. The changes that were made to some of the other instruments on board are mentioned also. The flight F3 took place on the evening of 19 March 1979, during a quiet interval within a period of repeated auroral activity. A weak negative magnetic bay of about 100 y (K = 2 ) was in progress at the time of launch : see § 7.2. of the report by Haüsler et al. [1982] . The aurora failed to evolve as anticipated, and the payload did not pass through any discrete arc. These relatively calm conditions, which disappointed the other experimenters, were ideal for determining whether the various modifications had improved the MF probe. In Section 8, where the results of the F3 experiment are presented, emphasis is therefore laid on analysis of the technical performance of the probe. The flight F4, on the evening of 31 March 1979, took place during a strong magnetic substorm ( p = 5+). At the time of launch, a discrete visual arc was present with a sharp northern edge, and the trajectory of the payload crossed this edge ; see § 7.3. of the report by Haüsler et al. [1982] . Stronger electric fields were encountered on this flight than on F3, and much of our study of the experimental results in Section 9 has been devoted to clarifying certain effects that appear to have been caused by these fields, and which resemble the spurious effects already observed on F2 inasmuch as they depended on spin phase and masked the interesting effects that we were looking for. The conclusions, presented in Section 10, are drawn from the results of all three successful flights. They substantiate the progress made in the development of the MF mutual-impedance probe as a means for measuring the field-aligned drift velocity of the thermal electrons, and indicate how, by further development, it might be made into a reliable instrument for this purpose

Electron plasma density deduced from lower oblique resonance measurements

International audienceIn a magnetoplasma, the amplitude of the lower oblique resonance in the mutual impedance of two electric antennas is very sensitive to the plasma frequency. This property can be used to measure the electron density in a simple way when the electron temperature and the magnetic field are known, provided also that the probe has been properly calibrated. As an application, densities are deduced from measurements made by a mutual‐impedance probe on a rocket in the auroral ionosphere. In the future, better practical design and theoretical modeling of the probe should make calibration unnecessary

Excitation of the lower oblique resonance by an artificial plasma jet in the ionosphere

Aboard the Porcupine rockets, bursts of noise were detected in the electron whistler range during the operation of a xenon plasma gun on a package ejected from the main payload. These observations can be interpreted in terms of excitation of the lower oblique resonance by instabilities associated with the motion of the xenon ion beam through the ionospheric plasma

Initial Survey of the Wave Distribution Functions for Plasmaspheric Hiss Observed by ISEE I • F Lsrsvvgs 2 M PARROT, 2 L CAm6 •

International audienceMulticomponent ELF/VLF wave data from the ISEE 1 satellite have been analyzed with the aim of identifying the generation mechanism of plasmaspheric hiss, and especially of determining whether it involves wave propagation on cyclic trajectories. The data were taken from four passes of the satellite, of which two were close to the geomagnetic equatorial plane and two were farther from it; all four occurred during magnetically quiet periods. The principal method of analysis was calculation of the wave distribution functions. The waves appear to have been generated over a wide range of altitudes within the plasmasphere, and most, though not all, of them were propagating obliquely with respect to the Earth's magnetic field. On one of the passes near the equator, some wave energy was observed at small wave normal angles, and these waves may have been propagating on cyclic trajectories. Even here, however, obliquely propagating waves were predominant, a finding that is difficult to reconcile with the classical quasi-linear generation mech•sm or its variants. The conclusion is that another mechanism, probably nonlinear, must have been generating most of the hiss observed on these four passes