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  • GEOPHYSICS  (5)
  • 1990-1994  (3)
  • 1980-1984  (2)
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  • GEOPHYSICS  (5)
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Year
  • 1
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    Temporal variations in the Siple Station conjugate area (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The Siple Station conjugate locations in the Northern Hemisphere are examined for the epoch 1975-1990 according to the predictions of three internal source geomagnetic field models (1GRF 1980, Magsat 1980, Barraclough 1975) and one external field model (Mead/Fairfield) under quiet and disturbed conditions. The conjugate location systematically changes in the interval studied, making it imperative that changes be made in the locations of the Northern Hemisphere geophysical stations during the reactivation of Siple Station in 1985-1987.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 89; 5655-565
    Format: text
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  • 2
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    On the relationship between morning sector irregular magnetic pulsations and field aligned currents (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: For three magnetically disturbed days in early 1980, data from south polar masses of the Magsat satellite are compared with data from search coil magnetometer, riometer, and photometer instrumentation at Siple, Antarctica. It is found that during each Magsat polar pass in the morning sector, the level of Pi 1 activity correlates well with the intensities of three-dimensional current systems. Fine structure is often observed in the field-aligned currents during periods of intense Pi activity. Among the Birkeland currents are 2-s to 10-s (16-80 km) structured perturbations; these are evident in the transverse components of the field and are thought to indicate filamentary currents. Pi 1 amplitudes are found to be considerably larger when region 2 Birkeland currents are overhead than when they are not. In one case, detailed features are identified in the high-resolution Magsat magnetic field data that may be current fluctuations related to asymmetric Pi 1.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 89; 1602-161
    Format: text
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  • 3
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    A case study of lightning, whistlers, and associated ionospheric effects during a substorm particle injection event (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The relationships among cloud-to-ground (CG) lightning, sferics, whistlers, VLF amplitude perturbations, and other ionospheric phenomena occurring during substorm events were investigated using data from simultaneous ground-based observations of narrow-band and broad-band VLF radio waves and of CG lightning made during the 1987 Wave-Induced Particle Precipitation campaign conducted from Wallops Island (Virginia). Results suggest that the data collected on ionospheric phenomena during this event may represent new evidence of direct coupling of lightning energy to the lower ionosphere, either in conjunction with or in the absence of gyroresonant interactions between whistler mode waves and electrons in the magnetosphere.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 97; 65-75
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  • 4
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    The role of the ionosphere in coupling upstream ULF wave power into the dayside magnetosphere (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: A series of recent studies of Pc 3 magnetic pulsations in the dayside outer magnetosphere has given new insights into the possible mechanisms of entry of ULF wave power into the magnetosphere from a bow shock-related upstream source. A comparison is made of data from two 10-hour intervals on successive days in April 1986 and then a possible model for transmission of pulsation signals from the magnetosheath into the dayside magnetosphere is presented. Clear interplanetary magnetic field magnitude control of dayside resonant harmonic pulsations and band-limited very high latitude pulsations, as well as pulsation-modulated precipitation of what appear to be magnetosheath/boundary layer electrons are shown. It is believed that this modulated precipitation may be responsible for the propagation of upstream wave power in the Pc 3 frequency band into the high-latitude ionosphere, from whence it may be transported throughout the dayside outer magnetosphere by means of an 'ionospheric transistor'. In this model, modulations in ionospheric conductivity caused by cusp/cleft precipitation cause varying ionospheric currents with frequency spectra determined by the upstream waves; these modulations will be superimposed on the Birkeland currents, which close via these ionospheric currents. Modulated region 2 Birkeland currents will in turn provide a narrow-band source of wave energy to a wide range of dayside local times in the outer magnetosphere.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 96; 1527-154
    Format: text
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  • 5
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    Ionospheric signatures of cusp latitude Pc 3 pulsations (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Search coil magnetometer, riometer, photometer, and ELF-VLF receiver data obtained at South Pole Station and McMurdo, Antarctica during selected days in March and April 1986 are compared. Narrow-band magnetic pulsations in the Pc 3 period range are observed simultaneously at both stations in the dayside sector during times of low IMF cone angle, but are considerably stronger at South Pole, which is located at a latitude near the nominal foot point of the dayside cusp/cleft region. Pulsations in auroral light at 427.8 nm wavelength are often observed with magnetic pulsations at South Pole, but such optical pulsations are not observed at McMurdo. The observations suggest that precipitating magnetosheathlike electrons at nominal dayside cleft latitudes are at times modulated with frequencies similar to those of upstream waves. These particles may play an important role, via modification of ionospheric currents and conductivities, in the transmission of upstream wave signals into the magnetosphere and in the generation of dayside high-latitude Pc 3 pulsations.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 2447-245
    Format: text
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