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  • 1
    Publication Date: 2011-08-19
    Description: An investigation of zircon data from the Mulcahy Lake gabbro, a 63 sq km layered mafic intrusion in the Wabigoon subprovince of Ontario, which show that the gabbro crystallized at 2733.2 +1.0, -0.9 Ma, is considered. It is shown that the gabbro intrudes tholeiites of the Crow Lake-Savant Lake greenstone belt. Whole rock samples and mineral separates from the Mulcahy Lake intrusion are dated by Rb-Sr, Sm-Nd, and Ar-30-Ar-40 techniques. Disturbances in the system are revealed by the Rb-Sr data and an initial Sr ratio of 0.7007 for an age of 2733 Ma is indicated by samples with low Rb/Sr ratios. The age determined for the Sm-Nd data is 2744 + or 55 Ma with an epsilon Nd value of +2.6 + or - 1.2 which indicates a source region depleted in a light rare earth element. Primary hornblende is analyzed for Ar-40/Ar-39 and an age of 2703 + or - 20 is obtained. Some implications for the development of greenstone-granite belts are discussed.
    Keywords: GEOPHYSICS
    Type: Earth and Planetary Science Letters (ISSN 0012-821X); 73; 2-3,
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  • 2
    Publication Date: 2013-08-31
    Description: Long term observations of relativistic electrons in the earth's outer magnetosphere show a strong solar cycle dependence with a prominent intensity maximum during the approach to solar minimum. This population therefore closely corresponds to the presence of high speed solar wind streams emanating from solar coronal holes. Using a numerical code, the precipitating electron energy deposition in the earth's upper and middle atmosphere were calculated. Observed events (typically persisting several days) would have maximum effect in the 40 to 60 km altitude range with peak energy depositions greater than 110 keV/cu cm-s. It is suggested that this electron population could play an important long term role in modulating lower D region ionization and middle atmospheric ozone chemistry. Methods are described of observing middle atmospheric and lower ionospheric effects of the electrons including balloon, riometer, and space-based ozone sensor systems. A particularly promising approach may involve the monitoring of global Schumann resonance modes which are sensitive to global changes in the properties of the earth-ionosphere cavity. Present work indicates that Schumann resonance properties are moderately correlated with the flux of precipitating relativistic electrons thus offering the possibility of continuously monitoring this aspect of magnetosphere-atmosphere coupling.
    Keywords: GEOPHYSICS
    Type: International Council of Scientific Unions, Middle Atmosphere Program. Handbook for MAP, volume 27; p 217-219
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  • 3
    Publication Date: 2011-08-19
    Description: Multi-satellite observations of energetic particle were made during the magnetospheric compression event of February 8, 1986. In the upstream region in the interplanetary medium (IPM) observations were made of magnetospheric leakage particles and specularly reflected solar wind ions.
    Keywords: GEOPHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 8; 9-10,
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  • 4
    Publication Date: 2019-07-12
    Description: A comprehensive review is presented of the characteristics of theta aurora as revealed from four imaging efforts with the DE 1 and 2 satellites. The theta aurora consists of an auroral oval with a sun-aligned arc extending from the dayside to the nightside sectors of the oval. The DE 1 spacecraft provided high altitude simultaneous measurements of the electric and magnetic fields and plasma and the DE 2 collected equivalent low altitude data on the four events. The plasma was found to convect sunward when the transpolar arc appeared, while the convection was antisunward in other regions over the polar cap. The arc plasmas featured field-aligned electron acceleration into the polar atmosphere and field-aligned current sheets, both of which were sparse over the rest of the polar cap. The ions originated in the ionosphere and the solar wind; ions over the rest of the polar cap mainly arrived from the magnetosphere. Further discussions are provided of the dominant electrons and ions and the associated flow directions into and out of the various regions of the pole, similarities between the transpolar arc and the auroral oval, and interactions between the ionosphere and the auroral phenomena.
    Keywords: GEOPHYSICS
    Type: AD-A167974 , Journal of Geophysical Research (ISSN 0148-0227); 91; 3177-322
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  • 5
    Publication Date: 2011-08-19
    Description: The first data obtained from the Earth Radiation Budget Experiment (ERBE) are presented. These data include emitted infrared radiation, albedo, and estimated scene types for Nov. 15, 1984, as well as measurements of the 'solar constant'. Images from the GOES on the same day are included for comparison with the ERBE scene identification. On an instantaneous basis, clouds appear colder and more reflective than seems to have been noted before. The experiment data will be applied to several key studies of cloud-radiation-climate interactions.
    Keywords: GEOPHYSICS
    Type: American Meteorological Society, Bulletin (ISSN 0003-0007); 67; 818-824
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  • 6
    Publication Date: 2011-08-19
    Description: Examination of many individual event periods in the ISEE 3 deep-tail data set has suggested that magnetospheric substorms produce a characteristic pattern of effects in the distant magnetotail. During the growth, or tail-energy-storage phase of substorms, the magnetotail appears to grow diametrically in size, often by many earth radii. Subsequently, after the substorm expansive phase onset at earth, the distant tail undergoes a sequence of plasma, field, and energetic-particle variations as large-scale plasmoids move rapidly down the tail following their disconnection from the near-earth plasma sheet. ISEE 3 data are appropriate for the study of these effects since the spacecraft remained fixed within the nominal tail location for long periods. Using newly available auroral electrojet indices (AE and AL) and Geo particle data to time substorm onsets at earth, superposed epoch analyses of ISEE 3 and near-earth data prior to, and following, substorm expansive phase onsets have been performed. These analyses quantify and extend substantially the understanding of the deep-tail pattern of response to global substorm-induced dynamical effects.
    Keywords: GEOPHYSICS
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  • 7
    Publication Date: 2011-08-19
    Description: Electromagnetic ion beam instabilities driven by cool ion beams at propagation parallel or antiparallel to a uniform magnetic field are studied using computer simulations. The elements of linear theory applicable to electromagnetic ion beam instabilities and the simulations derived from a one-dimensional hybrid computer code are described. The quasi-linear regime of the right-hand resonant ion beam instability, and the gyrophase bunching of the nonlinear regime of the right-hand resonant and nonresonant instabilities are examined. It is detected that in the quasi-linear regime the instability saturation is due to a reduction in the beam core relative drift speed and an increase in the perpendicular-to-parallel beam temperature; in the nonlinear regime the instabilities saturate when half the initial beam drift kinetic energy density is converted to fluctuating magnetic field energy density.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 91; 4188-420
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  • 8
    Publication Date: 2011-08-19
    Description: Both average and substorm conditions in the distant magnetotail were investigated using ISEE 3 magnetic field and plasma observations. The diameter of the tail, the strength of the lobe magnetic fields, and their dependence on downstream distance were all found to agree well with the flaring tail models of magnetopause geometry and pressure balance. The gradual filling of the lobes by mantle plasma reported in previous ISEE 3 studies were further investigated, and the results were found to be in qualitative agreement with leaky magnetopause model of Pilipp and Morfill (1978). The variations of plasma parameters with X + or -Y, and AE in the plasma sheet were examined. At all distances, the greatest tailward flow speeds were found to be directly proportional to the embedded southward B(z). THe magnitudes of tailward V(x) and southward B(z) are directly proportional to the level of substorm activity near the earth as measured by the AE index.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 90; 10
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  • 9
    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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  • 10
    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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