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  • Other Sources  (56)
  • GEOPHYSICS  (56)
  • 1
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    Observations of the dynamics of the polar thermosphere (1984)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: The dynamics of the polar thermosphere are examined by using observations made from the Dynamics Explorer 2 satellite. The results used in this study were obtained primarily from the Fabry-Perot interferometer (FPI) and the wind and temperature spectrometer (WATS) during the time period from September 1981 through January 1982. Two primary geophysical conditions were examined: these were the southern summer and the northern winter polar regions. The results support the conclusion that above 60 degrees of latitude the neutral winds are strongly controlled by ion/neutral frictional momentum transfer resulting from magnetospheric convection. This implies that the natural coordinate system within which to display the neutral winds in the high polar thermosphere is magnetic. The collected observations of this study were used to assess the validity of two of the large thermospheric general circulation models. The result of this assessment was that the models reasonably represent the vector winds at high altitudes but do not, at present, accurately simulate the thermodynamics of that regime.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 89; 5597-561
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  • 2
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    The CDAW-8 substorm event on 28 January 1983 - A detailed global study (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A small, isolated substorm with an expansion phase onset at 0739 UT on January 28, 1983 was well observed by ground-based instrumentation as well as by low- and high-altitude spacecraft. Because of the comprehensive nature of the data coverage, including ISEE-3 identification of plasmoid signatures in the deep tail (about 220 earth radii) associated with the substorm, a detailed timeline of the growth, expansion, and recovery phases of the substorm can be provided. The plasma, energetic particle, and field signatures at ISEE-3 are considered within the framework of the near-earth data. Quantitative estimates of substorm energy input and output relationships are made for this case, and the timing and physical dimensions of the deep tail disturbance implied are evaluated by the global observations available.
    Keywords: GEOPHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 8; 9-10,; 113-115
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  • 3
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    CDAW 8 observations of plasmoid signatures in the geomagnetic tail - An assessment (1989)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Magnetotail observations from the ISEE 3 distant (1983) tail mission taken during the Coordinated Data Analysis Workshop 8 (CDAW 8) A and G events are investigated. The ISEE 3 magnetic field, plasma, and energetic particle measurements taken in these two plasmoids have been analyzed and compared with various equilibrium structures and propagating waves/tail oscillation modes. Results indicate general agreement with either the closed-loop (Hones, 1977) or very small pitch angle flux rope (Hughes and Sibeck, 1987; Birn et al., 1989) models of plasmoid structure and poorer agreement with other hypotheses. Calculations based upon typical plasmoid and tail parameters are presented, indicating that the J and B force associated with the disconnected lobe field lines may be sufficient to accelerate plasmoids up to the speeds observed by ISEE 3. Overall, the energy expended in accelerating the plasmoids down the tail appears comparable to that dissipated in the inner magnetosphere and ionosphere. The study produces strong evidence in favor of the plasmoid model of substorm tail dynamics.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 94; 15153-15
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  • 4
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    Global auroral responses to magnetospheric compressions by shocks in the solar wind: Two case studies (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The global auroral responses to shocks in the solar wind at Earth were studied. The z-component of the interplanetary magnetic field, Bz, is negative ahead and behind the first shock and positive for the second case. A sudden-commencement geomagnetic storm develops in each case, with maximum D sub st 190 nT. An immediate auroral response is detected at all longitudes around the auroral oval, in which auroral luminosities increase by a factor of 2 to 3 with the first samples after each sudden commencement. The time delay in obtaining the first sample varies with local time from approx. 1 to 18 mins. No other significant variations in the aurora are associated with the immediate response. Beginning approx. 30 mins after each sudden commencement, the aurora becomes active and displays significant variations in its luminosity and spatial distribution. For Bz 0 an intense substorm develops. A sun-aligned transpolar arc forms when Bz 0, appearing first at local midnight as a polar arc and then lengthening sunward from the auroral oval across the polar cap to noon at an average speed of approx. 1 km/sec.
    Keywords: GEOPHYSICS
    Type: NASA-CR-177835 , NAS 1.26:177835 , U-OF-IOWA-85-11
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  • 5
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    Images of the earth's aurora and geocorona from the Dynamics Explorer mission (1985)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Several series of auroral and geocoronal images from th Dynamics Explorer Mission are presented and analyzed. It is found that the motion of the transpolar arc of a theta aurora is correlated with the y-component of the IMF; the arc motion is in the general direction of the y-component. In addition, a sequence of global images of a small auroral substorm shows the initial development of intense luminosities in a relatively small spatial region or 'bright spot' in the premidnight sector of the auroral oval and a subsequent appearance of an expanding area of lesser intensities at low latitudes and contiguous to the midnight boundary of the bright spot. Finally, a series of images of the geocorona in scattered solar Ly-alpha emissions is used to obtain a best-fit spherical model of atomic hydrogen densities in the earth's exosphere; a Chamberlain model provides an adequate fit to radial distances of 4.5 earth-radii, beyond which an exponential fit is used. The geocoronal tail is detected as an asymmetric increase in scattered Ly-alpha intensities in the antisolar direction.
    Keywords: GEOPHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 5; 4 19
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  • 6
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    The temporal evolution of a small auroral substorm as viewed from high altitudes with Dynamics Explorer 1 (1985)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A small auroral substorm is investigated with auroral imaging photometers carried on the spacecraft Dynamics Explorer 1. Initial brightening along the auroral oval and the subsequent westward and poleward motions of intense, localized emission regions are associated with auroral surges. Following substorm onset, another region of less intense emissions is observed to develop at lower latitudes and adjacent to the bright region near local midnight. This second region expands toward the east. The bright zone of auroral emissions associated with the surges is interpreted as the signature of electron acceleration along magnetic field lines threading the boundary layer of the plasma sheet in the magnetotail. The more diffuse, less intense region is identified with eastward-drifting electrons injected into the plasma sheet and ring current following substorm onset. No rapid poleward motion of the discrete aurora is detected during substorm recovery.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 12; 465-468
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  • 7
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    The temporal evolution of a small auroral substorm as viewed from high altitudes with Dynamics Explorer 1 (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A small auroral substorm is investigated with auroral imaging photometers carried on the spacecraft Dynamics Explorer 1. Initial brightening along the auroral oval and the subsequent westward and poleward motions of intense, localized emission regions are associated with auroral surges. Following substorm onset, another region of less intense emissions is observed to develop at lower latitudes and adjacent to the bright region near local midnight. This second region expands towards the east. The bright zone of auroral emissions associated with the surges is interpreted as the signature of electron acceleration along magnetic field lines threading the boundary layer of the plasma sheet in the magnetotail. The more diffuse, less intense region is identified with eastward-drifting electrons injected into the plasma sheet and ring current following substorm onset. No rapid poleward motion of the discrete aurora is detected during substorm recovery.
    Keywords: GEOPHYSICS
    Type: NASA-CR-176064 , NAS 1.26:176064 , UI-85-1 , AD-A157321
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  • 8
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    Geocoronal imaging with Dynamics Explorer - A first look (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The ultraviolet photometer of the University of Iowa spin-scan auroral imaging instrumentation on board Dynamics Explorer-1 has returned numerous hydrogen Lyman alpha images of the geocorona from altitudes of 570 km to 23,300 km (1.09 R sub E to 4.66 R sub E geocentric radial distance). The hydrogen density gradient is shown by a plot of the zenith intensities throughout this range, which decrease to near celestial background values as the spacecraft approaches apogee. Characterizing the upper geocorona as optically thin (single-scattering), the zenith intensity is converted directly to vertical column density. This approximation loses its validity deeper in the geocorona, where the hydrogen is demonstrated to be optically thick in that there is no Lyman alpha limb brightening. Further study of the geocoronal hydrogen distribution will require computer modeling of the radiative transfer. Previously announced in STAR as N83-20889
    Keywords: GEOPHYSICS
    Type: AD-A132344 , Geophysical Research Letters (ISSN 0094-8276); 10; July 198
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  • 9
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    Initial results from the DE-1 ozone imaging instrumentation (1985)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The first synoptic global-scale images of total column ozone are obtained in the sunlit hemisphere using the imaging instrumentation on board the spacecraft Dynamics Explorer 1 (DE-1). The total column ozone is determined using the backscatter ultraviolet technique. The high apogee altitude of the eccentric, polar orbit allows global-scale images of the terrestrial ozone field to be obtained in 12 minutes with good spatial resolution. Previous ozone-monitoring spacecraft have required much longer time periods for comparable spatial coverage because of their lower altitudes. The much higher altitude of DE-1 also provides hours of continuous imaging of features, as compared to minutes or seconds with previous spacecraft. Substantial short-term (less than 1 day) variations in the synoptic ozone field have been detected. This paper provides a brief description of this unique observation platform and shows the validity of the measured fields using comparisons with the Dobson network and with various meteorological measurements.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 12; 593-596
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  • 10
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    Universal time dependence of nighttime F region densities at high latitudes (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Coincident auroral-zone experiments using three incoherent-scatter radars at widely spaced longitudes are reported. The observational results demonstrate that, during the night, the F layer electron density is strongly dependent on the longitude of the observing site. Ionization patches were observed in the nighttime F region from the Chatanika and EISCAT radars, while densities observed from the Millstone radar were substantially smaller. The electron density within these maxima is larger at EISCAT than at Chatanika. When observed in the midnight sector auroral zone, these densities had a peak density at a high altitude of 360-475 km. The density was maximum when EISCAT was in the midnight sector and minimum when Millstone was in the midnight sector. A minimum in insolation in the auroral zone occurs at the UT when Millstone is in the midnight sector.
    Keywords: GEOPHYSICS
    Type: AD-A160574 , AFGL-TR-85-0222 , Journal of Geophysical Research (ISSN 0148-0227); 90; 4319-433
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