The WAVES investigation on the WIND spacecraft will provide comprehensive measurements of the radio and plasma wave phenomena which occur in Geospace. Analyses of these measurements, in coordination with the other onboard plasma, energetic particles, and field measurements will help us understand the kinetic processes that are important in the solar wind and in key boundary regions of the Geospace. These processes are then to be interpreted in conjunction with results from the other ISTP spacecraft in order to discern the measurements and parameters for mass, momentum, and energy flow throughout geospace. This investigation will also contribute to observations of radio waves emitted in regions where the solar wind is accelerated. The WAVES investigation comprises several innovations in this kind of instrumentation: among which the first use, to our knowledge, of neural networks in real-time on board a scientific spacecraft to analyze data and command observation modes, and the first use of a wavelet transform-like analysis in real time to perform a spectral analysis of a broad band signal.

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Waves: The Radio and Plasma Wave Investigation on the Wind Spacecraft

We review both observational and theoretical aspects of the generation of auroral radio emissions at the outer planets, trying to organize the former in a coherent frame set by the latter. Important results have been obtained in the past few years on these radio emissions at the five magnetized planets, from the observations of Ulysses at Jupiter and of Wind and other Global Geospace Science spacecraft in Earth orbit, from the reanalysis of Voyager data about Saturn, Uranus, and Neptune, from ground-based high frequency-time resolution and full polarization measurements, and from pioneering multispectral observations of the Jovian and Saturnian aurorae (radio/UV/IR). In parallel, considerable progress has been made in their generation theory (Cyclotron-Maser operating in small-scale, laminar, hot-plasma-dominated radio source structures), mostly on the basis of in situ observations of terrestrial radio sources. Particle acceleration and precipitation is also better documented, thanks to in situ measurements in the Earth auroral zones and to multispectral studies of Jupiter and Saturn. Finally, the modeling of the planetary magnetic field and magnetospheric plasma at these two planets has also been considerably improved. To organize the wealth of observational results within a coherent theoretical frame, we emphasize unresolved questions (e.g., planetary radio bursts generation) and contradictions and propose ways to answer them. Our ability, already significant, to perform remote sensing of magnetoplasmas at the giant planets and, hopefully, at other distant radio sources (solar, stellar) in the near future, depends on the good understanding of the physical processes underlying the generation of auroral electromagnetic emissions. The question of the existence of exoplanetary radio emissions and the possibility to detect and study them is briefly discussed.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/98JE01323

Auroral radio emissions at the outer planets: Observations and theories

This paper introduces and describes the radio and plasma wave investigation on the STEREO Mission: STEREO/WAVES or S/WAVES. The S/WAVES instrument includes a suite of state-of-the-art experiments that provide comprehensive measurements of the three components of the fluctuating electric field from a fraction of a hertz up to 16 MHz, plus a single frequency channel near 30 MHz. The instrument has a direction finding or goniopolarimetry capability to perform 3D localization and tracking of radio emissions associated with streams of energetic electrons and shock waves associated with Coronal Mass Ejections (CMEs). The scientific objectives include: (i) remote observation and measurement of radio waves excited by energetic particles throughout the 3D heliosphere that are associated with the CMEs and with solar flare phenomena, and (ii) in-situ measurement of the properties of CMEs and interplanetary shocks, such as their electron density and temperature and the associated plasma waves near 1 Astronomical Unit (AU). Two companion papers provide details on specific aspects of the S/WAVES instrument, namely the electric antenna system (Bale et al., Space Sci. Rev., 2007) and the direction finding technique (Cecconi et al., Space Sci. Rev., 2007).

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S/WAVES: The radio and plasma wave investigation on the STEREO Mission

Magnetic field measurements from the Ulysses space mission overthe south polar regions of the sun showed that the structure and properties of the three-dimensional heliosphere were determined by the fast solar wind flow and magnetic fields from the large coronal holes in the polar regions of the sun. This conclusion applies at the current, minimum phase of the 11-year solar activity cycle. Unexpectedly, the radial component of the magnetic field was independent of latitude. The high-latitude magnetic field deviated significantly from the expected Parker geometry, probably because of large amplitude transverse fluctuations. Low-frequency fluctuations had a high level of variance. The rate of occurrence of discontinuities also increased significantly at high latitudes.

https://science.sciencemag.org/content/sci/268/5213/1007.full.pdf

The heliospheric magnetic field over the South polar region of the sun.

This paper provides the essential tools for deriving quickly the quasi-thermal noise spectrum or the impedance of a given electric antenna near the plasma frequency, for calibration or diagnosis in space plasmas. The authors give simple analytical expressions and numerical results for either wire or sphere dipoles in an isotropic plasma with one or two Maxwellian electron populations. They include the contribution of the particles collected and/or emitted by the antenna surface. They also indicate some modifications brought about by using more complicated antenna geometries, and a drifting or a magnetized plasma. Finally, they give some conclusions for antenna design or data interpretation in plasma wave experiments.

/pdf/tool-kit-for-antennae-and-thermal-noise-near-the-plasma-mc2nyyu56q.pdf

Tool kit for antennae and thermal noise near the plasma frequency

Thermal noise spectroscopy was used to measure the density and temperature of the main (cold) electron plasma population during two hours around the point of closest approach of the International Cometary Explorer (ICE) to comet Giacobini-Zinner. The time resolution was 18 seconds in the plasma tail and 54 seconds elsewhere. Near the tail axis, the maximum plasma density was 670/cu cm and the temperature slightly above one volt. Away from the axis, the plasma density dropped to 100/cu cm over 2000 km, then decreased to 10/cu cm over 15,000 km; at the plasma tail, the density fluctuated between 10 and 30/cu cm, and the temperature, between 100,000 and 400,000 K. No evidence was found of grain impact on the spacecraft or antennas in the plasma tail. This yields an upper limit for the dust flux or particle mass, indicating either fluxes or masses in the tail smaller than those implied by models or an anomalous grain structure. Outside the tail, and particularly near 100,000 km from its axis, impulsive noises indicating plasma turbulence were observed.

https://science.sciencemag.org/content/sci/232/4748/370.full.pdf

Plasma diagnosis from thermal noise and limits on dust flux or mass in comet Giacobini-Zinner

A narrowband highly spin-modulated radio source has been observed with the radio astronomy experiment on ISEE 3 from a position 0.01 AU upstream of the earth. The source is interpreted as radio line emission generated at twice the local plasma frequency in the vicinity of the earth's bow shock by energetic particles. The bandwidth of the 2f(p) emission varies from less than 3 kHz to more than 20 kHz and is probably broadened by solar wind density variations across the source region. The 2f(p) source is visible about 50% of the time, and the true position of its centroid is usually located within 30 earth radii of the subsolar point, but at times is observed at a distance of up to 60 earth radii. But most of these variations might result from changes in the orientation of the polarization vector in a partially polarized source or from refraction across an electron density front.

The 2f/p/ circumterrestrial radio radiation as seen from ISEE 3

The noise voltage found at the terminals of an electric dipole antenna immersed in a hot plasma is calculated. The plasma is assumed stable and at rest. It is described as made of two maxwellian electron populations. A grid of calculated noise spectra is presented in normalized coordinates, and we give analytical expressions valid for frequencies much lower or larger than the plasma frequency fp or close to the noise peak. The antenna impedance is also calculated; in contrast to the noise spectrum, it is found to be very weakly dependent upon the hot population parameters. From these results one can calculate the response of a receiving system, thus enabling the actual measurement of the plasma parameters from the noise spectrum. Using ISEE 3 SBH experimental data, it is shown that the observations do fit the theoretical predictions over most of the frequency range. Plasma parameters are obtained and found in good agreement with results from the Los Alamos plasma analyzer on the same spacecraft. It appears that the high energy tail of the particle distribution function accounts for the peak noise voltages of several times 10−12 V²Hz−1 found at the terminals of a 45-m half-length dipole. The interpretation of these observations does not therefore require an unstable plasma. We discuss these results and show that more work should be done to explain an unpredicted increase of the spectrum below fp and to explain the weak spin modulation. Solving these remaining problems requires the introduction of ions and of the bulk and/or drift velocity into the calculations. Appendix A contains a partial justification of the assumption of a triangular current distribution on the antenna. The calculations are presented in appendix B.

Quasi‐thermal noise in a stable plasma at rest: Theory and observations from ISEE 3

ISEE observations of radiation at twice the solar wind plasma frequency.

Thermal plasma noise spectroscopy using the ICE radio receiver yielded the parameters of the two maxwellian populations approximating the comet plasma electron distribution. Within 150,000 km around closest approach, we observe three regions : 1) the inner one coincides with the low magnetic field region or plasma sheet ; over 1200 km the density is nearly constant at 650 cm−3; the overall profile, 5000 km wide, is assymetrical and shows a narrow spike on each side of the maximum ; the temperature is 16,000 K; 2) from 9000 to 20,000 km from the nucleus, the density decreases as R−2. The distribution is slightly assymetrical, the density higher on the south side. 3) Further away, the density and temperature fluctuate widely around about solar wind values. The hot electron pressure is much smaller than that of the cold electrons except near the edges of the plasma sheet where heating processes probably occur.

J. L. Steinberg

Papers

Plasma diagnosis from thermal noise and limits on dust flux or mass in comet Giacobini-Zinner

The 2f/p/ circumterrestrial radio radiation as seen from ISEE 3

Quasi‐thermal noise in a stable plasma at rest: Theory and observations from ISEE 3

ISEE observations of radiation at twice the solar wind plasma frequency.

Physical parameters for hot and cold electron populations in comet Giacobini-Zinner with the ICE radio experiment