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NASA NTRS1989

Plasma waves in the magnetotail of Uranus

Plasma wave phenomena observed during the Voyager 2 passing through the magnetotail of Uranus after its encounter with the planet on January 24, 1986 are described. The location of the wave events, their probable mode of propagation, and their association with various plasma and charged particle observations are presented. It was found that the most remarkable magnetotail plasma waves were inside the distance of about 23 Uranus radii, with an additional event occurring between about 48 and 56 Uranus radii. The frequency of these magnetotail plasma waves was found to be below about 100 Hz, extending down to the 10-Hz lower frequency limit of the receiver. The shape of the spectrum and the location of the wave activity near the boundary layer suggest that these waves may be similar to broadband electrostatic waves observed in similar regions of the earth's magnetotail.

Kurth, W. S.↗

NASA NTRS1987

Voyager 2 plasma wave observations at Uranus

At Uranus, the Voyager 2 plasma wave investigation observed very significant phenomena related to radio emissions, dust impacts, and magnetospheric wave-particle interactions. On January 19, 1986 (R = 270 R-sub U) the plasma wave investigation detected an intense radio burst at 31 and 56 kHz, and this provided the first indication that Uranus had a magnetosphere. During the encounter, more of these sporadic bursts were observed along with relatively continuous radio emissions extending down to 10 kHz, and a sporadic narrowband radio signal with f near 5 kHz. As Voyager passed through the ring plane, the plasma wave investigation recorded a large number of dust impacts. The Voyager 2 plasma wave instrument also detected many strong electromagnetic and electrostatic plasma waves, with intensity peaks in the region within 12 Uranus radii. These waves have characteristics that can interact strongly with the local plasma and with the trapped energetic particles, leading to precipitation into the atmosphere, charged particle acceleration, and charged particle diffusion. In addition, strong wave activity was detected in the region of the bow and shock and moderate levels in the magnetic tail.

Scarf, F. L.↗

NASA NTRS1977

A region of intense plasma wave turbulence on auroral field lines

Plasma wave measurements from the Hawkeye 1 and Imp 6 satellites show that a region of intense plasma wave turbulence occurs on high-latitude auroral field lines at altitudes ranging from a few thousand kilometers in the ionosphere to greater than 40 R-E in the distant magnetotail. Two distinct components are evident in the spectrum of this turbulence: (1) an intense quasi-electrostatic component called broadband electrostatic noise and (2) a weak whistler mode electromagnetic component called magnetic noise bursts. It is suggested that the plasma wave turbulence occurs on magnetic field lines which connect with regions of intense inverted V electron precipitation at low altitudes and with regions of intense earthward plasma flow in the distant magnetotail.

Gurnett, D. A.↗

NASA NTRS2016

The Potential for Ambient Plasma Wave Propulsion

A truly robust space exploration program will need to make use of in-situ resources as much as possible to make the endeavor affordable. Most space propulsion concepts are saddled with one fundamental burden; the propellant needed to produce momentum. The most advanced propulsion systems currently in use utilize electric and/or magnetic fields to accelerate ionized propellant. However, significant planetary exploration missions in the coming decades, such as the now canceled Jupiter Icy Moons Orbiter, are restricted by propellant mass and propulsion system lifetimes, using even the most optimistic projections of performance. These electric propulsion vehicles are inherently limited in flexibility at their final destination, due to propulsion system wear, propellant requirements, and the relatively low acceleration of the vehicle. A few concepts are able to utilize the environment around them to produce thrust: Solar or magnetic sails and, with certain restrictions, electrodynamic tethers. These concepts focus primarily on using the solar wind or ambient magnetic fields to generate thrust. Technically immature, quasi-propellantless alternatives lack either the sensitivity or the power to provide significant maneuvering. An additional resource to be considered is the ambient plasma and magnetic fields in solar and planetary magnetospheres. These environments, such as those around the Sun or Jupiter, have been shown to host a variety of plasma waves. Plasma wave propulsion takes advantage of an observed astrophysical and terrestrial phenomenon: Alfven waves. These are waves that propagate in the plasma and magnetic fields around and between planets and stars. The generation of Alfven waves in ambient magnetic and plasma fields to generate thrust is proposed as a truly propellantless propulsion system which may enable an entirely new matrix of exploration missions. Alfven waves are well known, transverse electromagnetic waves that propagate in magnetized plasmas at frequencies below the ion cyclotron frequency. They have been observed in both laboratory and astrophysical settings. On Earth, they are being investigated as a possible means for plasma heating, current drive, and momentum addition in magnetic confinement fusion systems. In addition, Alfven waves have been proposed as a mechanism for acceleration of the solar wind away from the sun.

THE POTENTIAL FOR AMBIENT PLASMA WAVE PROPULSION↗

NASA NTRS1995

Plasma wave evidence for lightning on Venus

Plasma wave data from the Pioneer Venus Orbiter provide the largest body of data cited as evidence for lightning on Venus. These data are also the most controversial, mainly because of the ambiguity in mode identification due to limited spectral information. We review some of the more recent studies of the plasma wave data at Venus, and we demonstrate that the characteristics of the 100 Hz waves are consistent with whistler-mode waves propagating vertically from below the ionosphere. We further show that in situ instabilities are too weak to generate whistler-mode waves, mainly because the thermal pressure is comparable with the magnetic field pressure in the ionosphere of Venus. The lower hybrid drift instability has also been suggested as an alternative source for the 100 Hz waves. However, the wave properties are more consistent with whistler-mode propagation; the lower hybrid dirft instability requires very short gradient scale lengths to overcome damping due to collisions. We also note that an apparent association between Langmuir probe anomalies and 100 Hz waves is much lower than previously reported, once we apply a consistent intensity threshold for identifying wave bursts. The lightning hyposthesis remains the most probable explanation of the plasma waves detected at low altitudes in the nightside ionosphere of Venus.

Strangeway, Robert J.↗

NASA NTRS1981

Energetic electrons and plasma waves associated with a solar type III radio burst

Detailed in situ observations from the ISEE 3 spacecraft of energetic electrons, plasma waves, and radio emission for the type II solar radio burst of February 17, 1979, are presented. The reduced, one-dimensional electron distribution function is constructed as a function of time. Since the faster electrons arrive before the slower ones, a bump on tail distribution forms which is unstable to the growth of Langmuir waves. The plasma wave growth computed from the distribution function agrees well with the observed onset of the Langmuir waves, and there is qualitative agreement between variations in the plasma wave levels and in the development of regions of positive slope in the function. The evolution of the function, however, predicts far higher plasma wave levels than those observed. The maximum levels observed are approximately equal to the threshold for nonlinear wave processes, such as oscillation two-stream instability and soliton collapse.

Lin, R. P.↗

NASA NTRS1982

Current status of IMS plasma wave research

The present investigation is concerned with a review of the status of magnetospheric plasma wave science as a result of the International Magnetospheric Study (IMS). The presence of an international effort has supported the development and completion of the numerous magnetospheric science spacecraft launched during the IMS, including GEOS, ISEE, and EXOS B. Ground-based VLF observations are considered along with coordinated ground-based and satellite observations. During the IMS, plasma wave research using satellite data has covered a wide range of subjects. Attention is given to magnetospheric electrostatic emissions, magnetospheric electromagnetic plasma waves, continuum radiation, auroral kilometric radiation, auroral zone plasma waves, plasma waves in the magnetosheath and near the mangetopause, and plasma waves at the bow shock.

Anderson, R. R.↗

NASA NTRS1991

Plasma waves in planetary magnetospheres

The plasma wave spectra are presented for the magnetospheres of five planets (the earth, Jupiter, Saturn, Uranus, and Neptune). A general comparison of the various plasma wave modes at each of the planets is provided using a common format for displaying the spectra. Results show that, in spite of great differences in the magnetospheres' sizes, heliocentric distances, energy sources, plasma sources, and magnetic dipole orientations between different planets, many of the same types of wave modes are present in each of the five magnetospheres. However, there are great differences in the relative and absolute intensity of some of the wave modes.

Kurth, W. S.↗

NASA NTRS1985

The menagerie of geospace plasma waves

The sounding rocket and satellite observations of space plasma waves within geospace in the frequency range from millihertz to megahertz are studied. Characteristic frequencies and source mechanisms of the plasma waves are described. The use of the Dynamic Explorer-1 Plasma Wave Instrument spectrograms to represent the plasma wave antenna and receiver system of geospace is examined. The ray tracing technique calculates the path of energy flow; the equations required for the analysis are presented. Cross-correlation of the wave electric and magnetic components provide data used to calculate the wave polarization, the direction of propagation, and the wave distribution function.

Shawhan, S. D.↗

NASA NTRS1983

Plasma waves in planetary magnetospheres

Research conducted within the last four years on plasma waves in the terrestrial magnetosphere as well as those of Jupiter and Saturn is reviewed. Studies aimed at the characterization of plasma wave emissions in the earth's magnetosheath and magnetopause are considered, together with investigations of the characteristics and mechanisms of electron cyclotron harmonic and upper hybrid resonance waves, nonthermal continuum radiation, auroral kilometric radiation, chorus, hiss and whistler-mode turbulence, whistlers, power line radiation, ion cyclotron waves, an ionospheric irregularities and instabilities. Experimental studies based on the injection of waves or plasma into the ionosphere and plasma waves in the laboratory are also examined. In situ Voyager data and radio astronomical observations of Jupiter are discussed as they relate to the plasma waves detected in the Jovian mgnetosheath and magnetopause, outer and inner magnetosphere and magnetotail, as well as the Jovian radio emission. In the case of Saturn, particular attention is given to the emissions observed during the Voyager encounter with the planet, its rings and Titan.

Anderson, R. R.↗

NASA NTRS1981

Plasma waves associated with energetic particles streaming into the solar wind from the earth's bow shock

Plasma wave and plasma data from ISEE 1 and 2 are examined. In the upstream solar wind, three dominant types of plasma waves are observed which are associated with energetic particle streams coming from the bow shock: ion acoustic waves, electron plasma oscillations, and whistler mode waves. The ion acoustic waves occur simultaneously with either ion beams or a dispersed ion population in the energy range from 0.5 to greater than 45 keV. The electron plasma oscillations are long-wavelength, nearly monochromatic electrostatic waves which are closely correlated with the flux of low-energy electrons, especially in the 0.2-1.5 keV range. Electromagnetic waves with frequencies below 200 Hz are observed when either ion beams or dispersed ion distributions are present; for these waves the refractive index determined from the wave B to E ratio is consistent with whistler mode radiation.

Anderson, R. R.↗

NASA NTRS1996

Plasma Waves in the Magnetosheath of Venus

Research supported by this grant is divided into three basic topics of investigation. These are: (1) Plasma waves in the Venus magnetosheath, (2) Plasma waves in the Venus foreshock and solar wind, (3) plasma waves in the Venus nightside ionosphere and ionotail. The main issues addressed in the first area - Plasma waves in the Venus magnetosheath - dealt with the wave modes observed in the magnetosheath and upper ionosphere, and whether these waves are a significant source of heating for the topside ionosphere. The source of the waves was also investigated. In the second area - Plasma waves in the Venus foreshock and solar wind, we carried out some research on waves observed upstream of the planetary bow shock known as the foreshock. The foreshock and bow shock modify the ambient magnetic field and plasma, and need to be understood if we are to understand the magnetosheath. Although most of the research was directed to wave observations on the dayside of the planet, in the last of the three basic areas studied, we also analyzed data from the nightside. The plasma waves observed by the Pioneer Venus Orbiter on the nightside continue to be of considerable interest since they have been cited as evidence for lightning on Venus.

Strangeway, Robert J.↗

NASA NTRS1979

Initial results from the ISEE-1 and -2 plasma wave investigation

A survey of initial results from the plasma-wave investigation on the ISEE 1 and 2 spacecraft is presented. The plasma-wave instruments employed are designed to provide measurements of the electric and magnetic fields of plasma waves over the frequency range from about 5 Hz to 300 kHz. Several representative satellite passes are analyzed in detail and discussed. The results considered are shown to demonstrate the very high-quality data being obtained with the instruments and to illustrate the wide range of magnetospheric plasma-physics problems that can be treated with the ISEE spacecraft. Comparisons of plasma-wave spectra between the two spacecraft are performed which indicate the great advantages of using two spacecraft in similar orbits to unravel the complex spatial and temporal variations that occur in the magnetosphere.

Gurnett, D. A.↗

NASA NTRS2001

Electrostatic Electron Cyclotron Waves Observed by the Plasma Wave Instrument on Board Polar

We report the results of an investigation of waves observed by the Polar spacecraft at high altitudes and latitudes and at frequencies just above the cyclotron frequency. These observations are made frequently when the spacecraft is over the polar cap as well as near the dayside cusp and near the nightside auroral region, and observations are made for ratios of plasma frequency to cyclotron frequency, f(sub p)/f(sub c) = 1. Using the six-channel high-frequency waveform receiver (HFWR) on board the spacecraft, which can provide three-axis electric and three-axis magnetic field measurements, we attempt to identify the wavemode of these emissions and investigate possible source mechanisms including low-energy electron beams. We further observe electromagnetic emission associated with upper hybrid waves near and within the plasmasphere. This emission is consistent with both Z and O modes.

Menietti, J. D.↗

NASA NTRS1989

First plasma wave observations at Neptune

The Voyager 2 plasma wave instrument detected many familiar plasma waves during the encounter with Neptune, including electron plasma oscillations in the solar wind upstream of the bow shock, electrostatic turbulence at the bow shock, and chorus, hiss, electron cyclotron waves, and upper hybrid resonance waves in the inner magnetosphere. Low-frequency radio emissions, believed to be generated by mode conversion from the upper hybrid resonance emissions, were also observed propagating outward in a disklike beam along the magnetic equatorial plane. At the two ring plane crossings many small micrometer-sized dust particles were detected striking the spacecraft. The maximum impact rates were about 280 impacts per second at the inbound ring plane crossing, and about 110 impacts per second at the outbound ring plane crossing. Most of the particles are concentrated in a dense disk, about 1000 kilometers thick, centered on the equatorial plane. However, a broader more tenuous distribution also extends many tends of thousands of kilometers from the equatorial plane, including over the northern polar region.

Gurnett, D. A.↗

NASA NTRS1976

Plasma waves in the distant magnetotail

The results of an extensive study of plasma waves in the distant magnetotail on the basis of measurements from the Imp 8 spacecraft are discussed. The plasma measurements are compared with plasma and magnetic field measurements described by Frank et al. (1976) to study the relationship of the plasma waves to the various plasma regimes found in the distant magnetotail. Three distinctly different types of plasma wave turbulence in the distant magnetotail are detected. The first, most frequently occurring type of turbulence, consists of broadband electrostatic noise at frequencies between 10 Hz and a few kHz. The second, less frequent type of plasma wave turbulence consists of intense (100 milligamma) bursts of low frequency (10 to 300 Hz) magnetic noise. The third, least frequent type of turbulence consists of electrostatic waves near harmonics of the electron gyrofrequency.

Gurnett, D. A.↗

NASA NTRS1991

Cometary plasma waves and instabilities

Various plasma waves and instabilities that have been observed near comets are discussed. Observational results are ordered by plasma parameters and compared with specific instabilities. The variation in the cometary ion and electron beam densities and velocities are studied by examining regions far from and near the comet nucleus. Spacecraft observations relevant to nonlinear wave evolution, wave cascading, and the development of turbulence are reviewed. The implications of the results for wave-particle interactions - linear, nonlinear, resonant, and nonresonant - and their effects on stochastic particle acceleration are addressed. Higher-frequency ELF/VLF wave observations are also reviewed, and comparisons between the various measurements are made.

Tsurutani, Bruce T.↗

NASA NTRS1989

A statistical study of ELF-VLF plasma waves at the magnetopause

ISEE 1 plasma wave data are used to study the broadband ELF-VLF plasma waves at the magnetopause. Enhanced wave intensities are detected at 85 percent of all magnetopause crossings. Wave amplitudes vary from event to event and even with a single event. Wave spectra averaged over many passes, however, are similar at dawn, noon, and dusk local hours. The only parameter correlated with wave intensity is the magnitude of the Z component of the magnetosheath magnetic field. The results place strong constraints on any proposed generation mechanism for the broadband magnetopause boundary layer waves.

Tsurutani, Bruce T.↗