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  • GEOPHYSICS  (46)
  • Lunar and Planetary Science and Exploration  (1)
  • Spacecraft Propulsion and Power  (1)
  • nonlinear modeling  (1)
  • 1990-1994  (49)
Collection
Keywords
Publisher
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Year
  • 1
    Electronic Resource
    Electronic Resource
    Separation of spin synchronized signals (1994)
    Springer
    Annals of the Institute of Statistical Mathematics 46 (1994), S. 405-428 
    Details
    ISSN: 1572-9052
    Keywords: Time series ; Bayesian approach ; outlier detection ; smoothing ; nonlinear modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract In the measurements of VLF electric fields with the Pioneer Venus spacecraft in sunlight, spin synchronized signals often dominate over the naturally generated emissions. We present a method to separate natural emissions from the several possible sources of noise. Our major objective by this method is not to remove all spin modulation, but to effectively subtract the background noise caused by the identifiable noise sources. Examination of the data shows that the background spin synchronized noise is quite sensitive to ϑ(n), the angle between the sense axis and the solar direction. We model the observed data asy(n)=w(n)t(n)f(ϑ(n))+x(n), wheref(ϑ) represents the phase response of the background noise andx(n) is the estimated natural emissions.t(n) andw(n) are the long-term trend component and time- and phase-independent component of the intensity of the background noise, respectively. The method to decomposey(n) is based on the Bayesian approach which has been recently applied to various inversion problems such as nonstationary time series modeling and image reconstruction. In this procedure, the estimated parametersw(n),t(n),f(ϑ), andx(n) can be determined automatically. We will describe the Bayesian scheme and its application to the Pioneer Venus VLF electric field data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00773508
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    Paper (German National Licenses)
    Fulltext
  • 2
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    The electron edge of the low latitude boundary layer during accelerated flow events (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Magnetosheath plasma entering the earth's magnetosphere to populate the low latitude boundary layer, LLBL, is often accelerated to speeds considerably greater than are observed in the adjacent magnetosheath. Measurements made during such accelerated flow events reveal separate electron and ion edges to the LLBL, with the electron edge being found earthward of the ion edge. Plasma electron velocity distributions observed at the earthward edge of the LLBL are often highly structured, exhibiting large asymmetries parallel and antiparallel, as well as perpendicular, to the local magnetic field. These features can consistently be interpreted as time-of-flight effects on recently reconnected field lines, and thus are strong evidence in support of the reconnection interpretation of accelerated plasma flow events.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 17; 1833-183
    Format: text
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  • 3
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    Cold ion beams in the low latitude boundary layer during accelerated flow events (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Measurements made with the Fast Plasma Experiment on ISEE 1 and 2 reveal that accelerated beams of cold (1-30 eV for H/+/) ions are present sporadically on reconnected field lines within the low latitude boundary layer (LLBI). H(+) normally is the major constituent of these beams, but He(+) and O(+) are also occasionally detected in variable concentrations. Because of the low temperatures and the compositional makeup of these beams, the ionosphere must ultimately be the source of these ions. Observed beam speeds (between 120 and 250 km/s) are always less than that of the magnetosheath ions which penetrate into the LLBL on reconnected field lines, but both ion populations share the same E x B convective drift. Analysis reveals that reflection at the magnetopause cannot be the mechanism accelerating these ions. A more likely possibility is that the ions are accelerated primarily by the large transverse drift of recently reconnected field lines.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 17; 2245-224
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  • 4
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    Maximizing the Scientific Return of Low Cost Planetary Missions Using Solar Electric Propulsion(abstract) (1994)
    In:  Other Sources
    Details
    Publication Date: 2018-06-08
    Description: After many years of development, solar electric propulsion is now a practical low cost alternative for many planetary missions. In response to the recent Discovery AO, we and a number of colleagues have examined the scientific return from a missioon to map the Moon and then rendezvous with a small body. In planning this mission, we found that solar electric propulsion was quite affordable under the Discovery guidelines, that many targets could be reached more rapidly with solar electric propulsion than chemical propulsion, that a large number of planetary bodies were accessible with modest propulsion systems, and that such missions were quite adaptable, with generous launch windows which minimized mission risks. Moreover, solar electric propulsion is ideally suited for large payloads requiring a large amount of power.
    Keywords: Spacecraft Propulsion and Power
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  • 5
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    (abstract) A Solar Electric Propulsion Mission to the Moon and Beyond! (1994)
    In:  Other Sources
    Details
    Publication Date: 2018-06-08
    Description: The technological development of solar electric propulsion has advanced significantly over the last few years. Mission planners are now seriously studying which missions would benefit most from solar electric propulsion (SEP) and NASA's Solar System Exploration Division is contributing funding to ground and space qualification tests. In response to the impending release of NASA's Announcement of Opportunity for Discovery class planetary missions, we have undertaken a pre-Phase A study of a SEP mission to the Moon. This mission will not only return a wealth of new scientific data but will open up a whole new era of planetary exploration.
    Keywords: Lunar and Planetary Science and Exploration
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  • 6
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    The magnetopause (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The magnetopause is the interface between the shocked solar wind in the magnetosheath and the geomagnetic field and plasma in the magnetosphere. This interface is far from simple because both sides of the interface contain magnetized plasma. As a result, there are boundary layers on both sides of the interface so the resulting structure is many-ion-gyroradii thick. There is also substructure which may be much less than an ion gyroradius in thickness. The structure of the magnetopause is also sensitive to the Mach number and beta of the plasma. When the beta is very high, the magnetopause resembles a slow mode wave. When the IMF is southward and the Mach number and/or beta is low the plasma is accelerated much as Dungey predicted. However, at other times reconnection seems to be less steady and perhaps patchy. Ropelike structures are seen which may be connected to the magnetosphere. These structures, which have been called FTEs, are still not fully understood.
    Keywords: GEOPHYSICS
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  • 7
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    The magnetosphere (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The present state of knowledge concerning the magnetosphere is reviewed. The magnetospheric cavity, the energization of the magnetosphere, the interior of the magnetosphere, and the aurora are discussed.
    Keywords: GEOPHYSICS
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  • 8
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    Observational test of hot flow anomaly formation by the interaction of a magnetic discontinuity with the bow shock (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The formation of a hot flow anomaly (HFA) observed near the Earth's bow shock appears to be due to the interaction between the bow shock and an impinging discontinuity in the upstream plasma. Recent single-particle and 2D hybrid numerical studies have suggested that such an interaction will produce an HFA only if the motional electric field in the ambient plasma points toward the discontinuity, thereby focusing shock-reflected ions into it. We perform a test of this electric field orientation for a set of nine HFA events observed by the ISEE spacecraft and described previously in the literature. Under the assumption that the discontinuities were tangential, the predicted electric field orientation is found on at least one side of all nine observed HFAs (on the trailing edge of seven and the leading edge of five, and on both sides of three events). Further, there is evidence that asymmetries in the observed magnetic field signatures are related to the orientation of the motional electric field. The events in which the electric field points toward the discontinuity on both sides tend to be those with fairly symmetric flanking magnetic field enhancements.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 98; A9; p. 15,319-15,330.
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  • 9
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    Slow mode transition in the frontside magnetosheath (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Three magnetosheath passes with density enhancements in front of the magnetopause are studied with data from ISEE 1, 2, and 3. The density structure appears to be locally generated and slow mode in nature. In one pass when ISEE 1 and 2 were well separated, the motion of the density structure can be determined. The density structure appears to stand in the magnetosheath flow. Thus, it propagates upstream in the rest frame of the flow. The flow in and near the density structure appears to be closer to isothermal than adiabatic. The flow velocity decreases from super-slow to being close to the intermediate and slow mode velocities at the outer edge of the density structure. This study provides additional evidence that the density structure in front of the magnetopause is a slow mode transition in which the flow velocity decreases to the MHD slow mode velocity. The slow mode transition may consist of two wave fronts and a region with strong slow mode waves. This slow mode transition may play an important role in establishing the flow and field pattern near the magnetopause.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 97; A6 J; 8295-830
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  • 10
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    Observations of a new class of upstream waves with periods near 3 seconds (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: A new class of ULF waves with periods near 3 s in the earth's upstream region is found by examining the high time resolution magnetic field data from the ISEE spacecraft. These waves are observed in the part of the upstream region which is magnetically connected to the bow shock, but only when the solar wind plasma beta is high (greater than 1). The waves are always right-handed, nearly circularly polarized in the spacecraft frame. The directions of the wave vectors are in the general direction of the average magnetic field, and the waves are convected downstream in the spacecraft frame. This study of these waves has shown that they appear to be intrinsically left-handed ion cyclotron waves in the plasma rest frame.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 97; A3 M; 2917-292
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