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  • GEOPHYSICS  (452)
  • 550 - Earth sciences  (355)
  • PHYSICS, ATOMIC, MOLECULAR, AND NUCLEAR  (288)
  • 1995-1999  (414)
  • 1965-1969  (681)
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  • 1
    Publikationsdatum: 2019-07-13
    Beschreibung: Multi-instrument data sets from the ground and satellites at both low and high altitude have provided new results concerning substorm onset and its source region in the magnetosphere. Twenty-six out of 37 substorm onset events showed evidence of azimuthally spaced auroral forms (AAFs) prior to the explosive poleward motion associated with optical substorm onset. AAFs can span 8 hours of local time prior to onset and generally propagate eastward in the morning sector. Onset itself is, however, more localized spanning only about 1 hour local time. AAF onset occur during time periods when the solar wind pressure is relatively high. AAFs brighten in conjunction with substorm onset leading to the conclusion that they are a growth phase activity casually related to substorm onset. Precursor activity associated with these AAFs is also seen near geosynchronous orbit altitude and examples show the relationship between the various instrumental definitions of substorm onset. The implied mode number (30 to 135) derived from this work is inconsistent with cavity mode resonances but is consistent with a modified flute/ballooning instability which requires azimuthal pressure gradients. The extended source region and the distance to the open-closed field line region constrain reconnection theory and local mechanisms for substorm onset. It is demonstrated that multiple onset substorms can exist for which localized dipolarizations and the Pi 2 occur simultaneously with tail stretching existing elsewhere. These pseudobreakups can be initiated by auroral streamers which originate at the most poleward set of arc systems and drift to the more equatorward main UV oval. Observations are presented of these AAFs in conjunction with low- and high-altitutde particle and magnetic field data. These place the activations at the interface between dipolar and taillike field lines probably near the peak in the cross-tail current. These onsets are put in the context of a new scenario for substorm morphology which employs individual modules which operate independently or couple together. This allows particular substorm events to be more accurately described and investigated.
    Schlagwort(e): GEOPHYSICS
    Materialart: Journal of Geophysical Research (ISSN 0148-0227); 100; A5; p. 7937-7969
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Publikationsdatum: 2019-07-13
    Beschreibung: The dual jet aircraft Sprites94 campaign yielded the first color imagery and unambiguously triangulated physical dimensions and heights of upper atmospheric optical emissions associated with thunderstorm systems. Low light level television images, in both color and in black and white (B/W), obtained during the campaign show that there are at least two distinctively different types of optical emissions spanning part or all of the distance between the anvil tops and the ionosphere. The first of these emissions, dubbed 'sprites' after their elusive nature, are luminous structures of brief (less than 16 ms) duration with a red main body that typically spans the latitude range 50-90 km, and possessing lateral dimensions of 5-30 km. Faint bluish tendrils often extend downward from the main body of sprites, occasionally appearing to reach cloud tops near 20 km. In this paper the principal characteristics of red sprites as observed during the Sprites94 campaign are described. The second distinctive type of emissions, 'blue jets,' are described in a companion paper (Wescott et al., this issue).
    Schlagwort(e): GEOPHYSICS
    Materialart: Geophysical Research Letters (ISSN 0094-8276); 22; 10; p. 1205-1208
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Publikationsdatum: 2011-08-24
    Beschreibung: A nonlinear filtering method is introduced for the study of the solar wind -- magnetosphere coupling and related to earlier linear techniques. The filters are derived from the magnetospheric state, a representation of the magnetospheric conditions in terms of a few global variables, here the auroral electrojet indices. The filters also couple to the input, a representation of the solar wind variables, here the rectified electric field. Filter-based iterative prediction of the indices has been obtained for up to 20 hours. The prediction is stable with respect to perturbations in the initial magnetospheric state; these decrease exponentially at the rate of 30/min. The performance of the method is examined for a wide range of parameters and is superior to that of other linear and nonlinear techniques. In the magnetospheric state representation the coupling is modeled as a small number of nonlinear equations under a time-dependent input.
    Schlagwort(e): GEOPHYSICS
    Materialart: Journal of Geophysical Research (ISSN 0148-0227); 100; A3; p. 3495-3512
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Publikationsdatum: 2011-08-24
    Beschreibung: Initial observations of a newly documented type of optical emission above thunderstorms are reported. 'Blue jets', or narrowly collimated beams of blue light that appear to propagate upwards from the tops of thunderstorms, were recorded on B/W and color video cameras for the first time during the Sprites94 aircraft campaign, June-July, 1994. The jets appear to propagate upward at speeds of about 100 km/s and reach terminal altitudes of 40-50 m. Fifty six examples were recorded during a 22 minute interval during a storm over Arkansas. We examine some possible mechanisms, but have no satisfactory theory of this phenomenon.
    Schlagwort(e): GEOPHYSICS
    Materialart: Geophysical Research Letters (ISSN 0094-8276); 22; 10; p. 1209-1212
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Publikationsdatum: 2006-10-26
    Beschreibung: Preliminary data analysis of lifetimes of positive and negative pions
    Schlagwort(e): PHYSICS, ATOMIC, MOLECULAR, AND NUCLEAR
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Publikationsdatum: 2006-10-26
    Beschreibung: Prototype explosive assembly for large scale plane wave shock experiments on rock specimen in laboratory
    Schlagwort(e): GEOPHYSICS
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    Publikationsdatum: 2006-10-26
    Beschreibung: Fluorine-19 nuclear magnetic resonance spectra of trifluoroacetates of polyalkylene oxides
    Schlagwort(e): PHYSICS, ATOMIC, MOLECULAR, AND NUCLEAR
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    Publikationsdatum: 2011-08-11
    Beschreibung: Planar shock wave test assembly for simulating meteoritic impact on planetary rock surface
    Schlagwort(e): GEOPHYSICS
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
    Publikationsdatum: 2011-08-10
    Beschreibung: Relative signs of nuclear spin coupling constants in propylene oxide and indene oxide obtained from iterative analysis of NMR spectra
    Schlagwort(e): PHYSICS, ATOMIC, MOLECULAR, AND NUCLEAR
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
    Publikationsdatum: 2019-07-13
    Beschreibung: The poleward arc system of a double oval distribution is shown to activate at the end of the optical expansion phase signifying the beginning of substorm recovery. The velocity dispersed ion signature (VDIS) can exist coincident with this discrete aurora developing on the most poleward oval. Although the VDIS is usually associated with ion beams in the plasma sheet boundary layer, it is demonstrated that the ionospheric signature is not beamlike but distributed in pitch angle. At the time when the double oval begins to form, the magnetic field in the magnetotail lobe becomes less flared and can show Pc 5 period oscillations. Similar pulsations also exist in the ionosphere associated with the most poleward oval and with stationary surge formation. Theoretical considerations link this phenomenon with a wave source tailward of x(sub GSE) = -30R(sub E) and fast mode evanescent waves propagating earthward in the tail lobe region. In this case the magnetotail appears to act like a waveguide and the plasma sheet boundary layer as a resonance region. This implies that the coupling of this fast mode waves is with the plasma sheet boundary layer and not with dipolar like field lines. The implications of this for the reconnection model of substorms are discussed.
    Schlagwort(e): GEOPHYSICS
    Materialart: Journal of Geophysical Research (ISSN 0148-0227); 100; A7; p. 12,093-12,102
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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