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  • SOLAR PHYSICS  (8)
  • Geochemistry, Geophysics, Online Only, Planetary Science  (3)
  • 1
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    The low-frequency source of Saturns kilometric radiation (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publikationsdatum: 2018-10-05
    Beschreibung: Understanding how auroral radio emissions are produced by magnetized bodies requires in situ measurements within their source region. Saturn’s kilometric radiation (SKR) has been widely used as a remote proxy of Saturn’s magnetosphere. We present wave and plasma measurements from the Cassini spacecraft during its ring-grazing high-inclination orbits, which passed three times through the high-altitude SKR emission region. Northern dawn-side, narrow-banded radio sources were encountered at frequencies of 10 to 20 kilohertz, within regions of upward currents mapping to the ultraviolet auroral oval. The kilometric waves were produced on the extraordinary mode by the cyclotron maser instability from 6– to 12–kilo–electron volt electron beams and radiated quasi-perpendicularly to the auroral magnetic field lines. The SKR low-frequency sources appear to be strongly controlled by time-variable magnetospheric electron densities.
    Schlagwort(e): Geochemistry, Geophysics, Online Only, Planetary Science
    Print ISSN: 0036-8075
    Digitale ISSN: 1095-9203
    Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik
    Publiziert von American Association for the Advancement of Science (AAAS)
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
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    In situ collection of dust grains falling from Saturns rings into its atmosphere (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publikationsdatum: 2018-10-05
    Beschreibung: Saturn’s main rings are composed of 〉95% water ice, and the nature of the remaining few percent has remained unclear. The Cassini spacecraft’s traversals between Saturn and its innermost D ring allowed its cosmic dust analyzer (CDA) to collect material released from the main rings and to characterize the ring material infall into Saturn. We report the direct in situ detection of material from Saturn’s dense rings by the CDA impact mass spectrometer. Most detected grains are a few tens of nanometers in size and dynamically associated with the previously inferred "ring rain." Silicate and water-ice grains were identified, in proportions that vary with latitude. Silicate grains constitute up to 30% of infalling grains, a higher percentage than the bulk silicate content of the rings.
    Schlagwort(e): Geochemistry, Geophysics, Online Only, Planetary Science
    Print ISSN: 0036-8075
    Digitale ISSN: 1095-9203
    Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik
    Publiziert von American Association for the Advancement of Science (AAAS)
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
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    Dust grains fall from Saturns D-ring into its equatorial upper atmosphere (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publikationsdatum: 2018-10-05
    Beschreibung: The sizes of Saturn’s ring particles range from meters (boulders) to nanometers (dust). Determination of the rings’ ages depends on loss processes, including the transport of dust into Saturn’s atmosphere. During the Grand Finale orbits of the Cassini spacecraft, its instruments measured tiny dust grains that compose the innermost D-ring of Saturn. The nanometer-sized dust experiences collisions with exospheric (upper atmosphere) hydrogen and molecular hydrogen, which forces it to fall from the ring into the ionosphere and lower atmosphere. We used the Magnetospheric Imaging Instrument to detect and characterize this dust transport and also found that diffusion dominates above and near the altitude of peak ionospheric density. This mechanism results in a mass deposition into the equatorial atmosphere of ~5 kilograms per second, constraining the age of the D-ring.
    Schlagwort(e): Geochemistry, Geophysics, Online Only, Planetary Science
    Print ISSN: 0036-8075
    Digitale ISSN: 1095-9203
    Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik
    Publiziert von American Association for the Advancement of Science (AAAS)
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
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    Fine structure of Langmuir waves observed upstream of the bow shock at Venus (1994)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-24
    Beschreibung: 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.
    Schlagwort(e): SOLAR PHYSICS
    Materialart: Journal of Geophysical Research (ISSN 0148-0227); 99; A7; p. 13,363-13,371
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
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    Cassini radio and plasma wave investigation - Data compression and scientific applications (1993)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-24
    Beschreibung: 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.
    Schlagwort(e): SOLAR PHYSICS
    Materialart: British Interplanetary Society, Journal (ISSN 0007-094X); 46; 3; p. 115-120.
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
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    Heliospheric 2-3 kHz radio emissions and their relationship to large Forbush decreases (1995)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-04-02
    Beschreibung: 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.
    Schlagwort(e): SOLAR PHYSICS
    Materialart: Advances in Space Research (ISSN 0273-1177); 16; 9; p. (9)279-(9)290
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
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    Direction-finding measurements of type 3 radio bursts out of the ecliptic plane (1975)
    In:  CASI
    Details
    Publikationsdatum: 2019-07-13
    Beschreibung: 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.
    Schlagwort(e): SOLAR PHYSICS
    Materialart: 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
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
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    High-resolution spectrograms of ion acoustic waves in the solar wind (1979)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-06-27
    Beschreibung: High-resolution, frequency-time spectrograms of ion acoustic waves in the solar wind obtained by the Voyager spacecraft at distances of up to 1.7 AU are examined. The plasma wave instrument on board the Voyager spacecraft used to acquire the spectra employs an electric dipole antenna with a 16-channel step frequency receiver and a high-bit-rate waveform receiver to detect and measure the electric field of plasma waves. Voyager spectrograms show that the ion acoustic waves consist of narrowband, rapidly varying bursts, lasting a few seconds or less, usually in the range between the plasma ion and electron frequencies. Spectrograms taken at 1.7 AU are shown to be essentially identical to similar measurements taken upstream of the earth's magnetosphere, which are produced by suprathermal protons streaming into the solar wind from the bow shock, and to those taken upstream of interplanetary shocks.
    Schlagwort(e): SOLAR PHYSICS
    Materialart: AD-A075845 , Journal of Geophysical Research; 84; July 1
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
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    Direction-finding measurements of type III radio bursts out of the ecliptic plane (1976)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-06-27
    Beschreibung: A series of two-dimensional direction-finding measurements for three type III solar radio bursts is presented which is based on spin-modulation measurements from two satellites (IMP 8 and Hawkeye I) whose spin axes were nearly perpendicular to each other. The two-dimensional direction-finding technique is combined with a model of the solar-wind plasma density in order to provide determinations of type III source locations out of the ecliptic plane as well as information on the three-dimensional structure of the solar magnetic field at radial distances of 0.2 to 1.0 AU from the sun. The direction-finding technique is described in detail, characteristics of the bursts observed by the two satellites are summarized, and the solar-wind model is outlined. The results show that the source locations follow an Archimedean spiral when projected onto the ecliptic plane but usually follow a constant heliocentric latitude perpendicular to that plane. It is also found that measured source sizes are a factor of two larger than the angular sizes of previously reported solar-flare electron emissions, that the spin-modulation factor tends to be largest near the beginning of a type III event, and that the arrival direction of the radiation varies systematically during an event.
    Schlagwort(e): SOLAR PHYSICS
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
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    The heliocentric radial variation of plasma oscillations associated with type III radio bursts (1978)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-06-27
    Beschreibung: A survey is presented of all of the electron plasma oscillation events found to date in association with low-frequency type III solar radio bursts using approximately 9 years of observations from the Imp 6 and 8, Helios 1 and 2, and Voyager 1 and 2 spacecraft. Plasma oscillation events associated with type III radio bursts show a pronounced increase in both the intensity and the frequency of occurrence with decreasing heliocentric radial distance. This radial dependence explains why intense electron plasma oscillations are seldon observed in association with type III radio bursts at the orbit of the earth. Possible interpretations of the observed radial variation in the plasma oscillation intensity are considered.
    Schlagwort(e): SOLAR PHYSICS
    Materialart: Journal of Geophysical Research; 83; Sept. 1
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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