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  • 1
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    Fine structure of Langmuir waves observed upstream of the bow shock at Venus (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Highly structured Langmuir waves, also known as electron plasma oscillations, have been observed in the foreshock of Venus using the plasma wave experiment on the Galileo spacecraft during the gravity assist flyby on February 10, 1990. The Galileo wideband sampling system provides digital electric field waveform measurements at sampling rates up to 201,600 samples per second, much higher than any previous instrument of this type. The main Langmuir wave emission band occurs near the local electron plasma frequency, which was approximately 43 kHz. The Langmuir waves are observed to shift above and below the plasma frequency, sometimes by as much as 20 kHz. The shifts in frequency are closely correlated with the downstream distance from the tangent field line, implying that the shifts are controlled by the electron beam velocity. Considerable fine structure is also evident, with timescales as short as 0.15 ms, corresponding to spatial scales of a few tens of Debye lengths. The frequency spectrum often consists of beat-type waveforms, with beat frequencies ranging from 0.2 to 7 kHz, and in a few cases, isolated wave packets. The peak electric field strengths are approximately 1 mV/m. These field strengths are too small for strongly nonlinear processes to be important. The beat-type waveforms are suggestive of a parametric decay process.
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 99; A7; p. 13,363-13,371
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  • 2
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    Cassini radio and plasma wave investigation - Data compression and scientific applications (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The Radio and Plasma Wave Science (RPWS) experiment being built for the Cassini spacecraft will study a wide range of plasma and radio wave phenomena in the magnetosphere of Saturn and will also make valuable measurements during the cruise phase and at other encounters. A feature of data from wave receivers is the capability of producing vastly more data than the spacecraft telemetry link is capable of transmitting back to the Earth. Thus, techniques of on-board data compression and data reduction are important. The RPWS instrument has one processor dedicated to data compression tasks.
    Keywords: SOLAR PHYSICS
    Type: British Interplanetary Society, Journal (ISSN 0007-094X); 46; 3; p. 115-120.
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  • 3
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    Heliospheric 2-3 kHz radio emissions and their relationship to large Forbush decreases (1995)
    In:  Other Sources
    Details
    Publication Date: 2019-04-02
    Description: Two intense heliospheric 2-3 kHz radio emission events have been observed by Voyagers 1 and 2, the first in 1983-84 and the second in 1992-93. These radio emission events occurred about 400 days after large Forbush decreases in mid-1982 and mid-1991. Since Forbush decreases are indicative of a strong interplanetary shock propagating outward through the heliosphere, this temporal relationship provides strong evidence that the radio emissions are triggered by the interaction of a shock with one of the outer boundaries of the heliosphere. From the travel time and the known speed of the shock, the distance to the interaction region can be estimated and is well beyond 100 AU. At this great distance the plasma frequency at the terminal shock (100 to 200 Hz) is believed to be too small to explain the observed emission frequencies, which extend up to 3.6 kHz. For this reason, we have proposed that the interaction takes place at or near the heliopause, where remote sensing measurements show that the plasma frequency is in a suitable range (approximately 3 kHz) for explaining the radio emission. From the travel time and shock propagation speed, the radial distance to the heliopause has been calculated for various candidate solar events. After taking into account the likely deceleration of the shock, the heliopause is estimated to be in the range from about 110 to 160 AU.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 16; 9; p. (9)279-(9)290
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  • 4
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    Observations of a free-energy source for intense electrostatic waves (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Significant progress has been made in understanding intense electrostatic waves near the upper hybrid resonance frequency in terms of the theory of multiharmonic cyclotron emission using a classical loss-cone distribution function as a model. Recent observations by Hawkeye 1 and GEOS 1 have verified the existence of loss-cone distributions in association with the intense electrostatic wave events, however, other observations by Hawkeye and ISEE have indicated that loss cones are not always observable during the wave events, and in fact other forms of free energy may also be responsible for the instability. Now, for the first time, a positively sloped feature in the perpendicular distribution function has been uniquely identified with intense electrostatic wave activity. Correspondingly, we suggest that the theory is flexible under substantial modifications of the model distribution function.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters; 7; May 1980
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  • 5
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    Escaping nonthermal continuum radiation (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Gurnett (1975) provided details of the continuum radiation spectrum, separating the lower frequency trapped component from an escaping component at frequencies high enough to propagate freely out of the magnetosphere and into the solar wind. The primary motivation for the present investigation is related to the new ISEE observations which show that the escaping continuum radiation differs from the trapped component in several temporal and spectral characteristics. The observations of escaping nonthermal continuum radiation are considered, taking into account spectral and temporal characteristics of escaping continuum radiation and the source region of escaping continuum radiation. Attention is given to the relationship between escaping and trapped continuum radiation, and the relationship between terrestrial escaping continuum radiation and narrowband Jovian kilometric radiation
    Keywords: GEOPHYSICS
    Type: AD-A104719 , Journal of Geophysical Research; 86; July 1
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  • 6
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    Detailed observations of the source of terrestrial narrowband electromagnetic radiation (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Detailed observations are presented of a region near the terrestrial plasmapause where narrowband electromagnetic radiation (previously called escaping nonthermal continuum radiation) is being generated. These observations show a direct correspondence between the narrowband radio emissions and electron cyclotron harmonic waves near the upper hybrid resonance frequency. In addition, electromagnetic radiation propagating in the Z-mode is observed in the source region which provides an extremely accurate determination of the electron plasma frequency and, hence, density profile of the source region. The data strongly suggest that electrostatic waves and not Cerenkov radiation are the source of the banded radio emissions and define the coupling which must be described by any viable theory.
    Keywords: GEOPHYSICS
    Type: AD-A125949 , Geophysical Research Letters; 9; Dec. 198
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  • 7
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    Direction-finding measurements of auroral kilometric radiation (1975)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Direction-finding measurements with plasma wave experiments on the Hawkeye 1 and Imp 8 satellites are used to locate the source region of auroral kilometric radiation. This radiation has peak intensities between about 100 and 300 kHz and is emitted in intense sporadic bursts lasting for from half an hour to several hours. At peak intensity the total power emitted in this frequency range exceeds 1 billion W. The occurrence of this radiation is known to be closely associated with bright auroral arcs which occur in the local evening auroral regions. Hawkeye 1 provides direction-finding measurements of kilometric radiation from observations at high latitudes over the northern polar regions, and Imp 8 provides similar observations at large radial distances near the equatorial plane. Results from both satellites place the source of the intense auroral kilometric rdiation in the late local evening at about 22.0 hours LT and at a distance of about 0.75 earth radii from the polar axis of the earth.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 80; July 1
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  • 8
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    Electron distribution functions associated with electrostatic emissions in the dayside magnetosphere (1979)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The analysis deals with electron distribution functions constructed from ISEE-1 dayside observations of low-energy magnetospheric electrons at low latitudes. The discussion covers some examples corresponding to three distinct types of odd half harmonic electrostatic emissions, observed in the plasma wave experiment on ISEE-1, which occur between the electron cyclotron frequency and the upper hybrid frequency.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters; 6; Oct. 197
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  • 9
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    Direction-finding measurements of type 3 radio bursts out of the ecliptic plane (1975)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Direction-finding measurements with the plasma wave experiments on the HAWKEYE 1 and IMP 8 satellites are used to find the source locations of type 3 solar radio bursts in heliocentric latitude and longitude in a frequency range from 31.1 kHz to 500 kHz. Using an empirical model for the emission frequency as a function of radial distance from the sun the three-dimensional trajectory of the type 3 radio source can be determined from direction-finding measurements at different frequencies. Since the electrons which produce these radio emissions follow the magnetic field lines from the sun these measurements provide information on the three-dimensional structure of the magnetic field in the solar wind. The source locations projected into the ecliptic plane follow an Archimedian spiral. Perpendicular to the ecliptic plane the source locations usually follow a constant heliocentric latitude. With direction-finding measurements of this type it is also possible to determine the source size from the modulation factor of the received signals.
    Keywords: SOLAR PHYSICS
    Type: NASA-CR-146574 , U-OF-IOWA-75-45 , Workshop on Mech. for Solar Type 3 Radio Bursts; May 08, 1975 - May 09, 1975; Berkeley, CA; United States
    Format: application/pdf
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  • 10
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    A comparison of intense electrostatic waves near f-UHR with linear instability theory (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Intense electrostatic waves near the upper hybrid resonance frequency (f-UHR) have recently been detected near but beyond the plasmapause between + or -50 deg magnetic latitude at all local times. The paper shows that the electrostatic waves observed with the ISEE 1 plasma wave receiver near f-UHR are in qualitative agreement with linear theory of multicyclotron harmonic emissions. The peak amplitudes and bandwidths observed are similar to those calculated for maximum spatial growth rates. Measurements on Hawkeye of similar waves suggest that the electric field polarization is also consistent with theory. For a wide range of plasma parameters, nonconvective instability or large spatial growth rates occur within the cyclotron band encompassing the cold upper hybrid frequency.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters; 6; June 197
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