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  • 1
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    Observations of ionospheric electric fields above atmospheric weather systems (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We report on the observations of a number of quasi-dc electric field events associated with large-scale atmospheric weather formations. The observations were made by the electric field experiment onboard the San Marco D satellite, operational in an equatorial orbit from May to December 1988. Several theoretical studies suggest that electric fields generated by thunderstorms are present at high altitudes in the ionosphere. In spite of such favorable predictions, weather-related events are not often observed since they are relatively weak. We shall report here on a set of likely E field candidates for atmospheric-ionospheric causality, these being observed over the Indonesian Basin, northern South America, and the west coast of Africa; all known sites of atmospheric activity. As we shall demonstrate, individual events often be traced to specific active weather features. For example, a number of events were associated with spacecraft passages near Hurricane Joan in mid-October 1988. As a statistical set, the events appear to coincide with the most active regions of atmospheric weather.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 99; A10; p. 19,475-19,483
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  • 2
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    PULSAUR 2: A sounding rocket project to study pulsating aurora and related phenomena (1995)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The second pulsating aurora (PULSAUR 2) rocket was a comprehensively instrumented rocket for the study of the generating mechanisms of pulsating auroras and their related atmospheric and ionospheric effects. It carried instruments to measure electrons and ions over a wide range of energies and pitch angles, optical emissions and X-rays, direct currents and alternating currents, magnetic fields, electron densities and temperatures. The rocket was flown from Andoeya, Norway on 9 February 1994, during good auroral and optical conditions, and reached an altitude of 291.5 km. Coordinated measurements were made from the rocket range by television cameras, photometers, magnetometers, riometers and very low frequency receivers. Ionospheric parameters were measured by the EISCAT radar. The main objectives and performance of the project are discussed, and some of the data obtained are mentioned.
    Keywords: GEOPHYSICS
    Type: NASA-TM-111282 , NAS 1.15:111282 , ESA, Proceedings of 12th ESA Symposium on European Rocket and Balloon Programmes and Related Research; p 227-232
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  • 3
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    Focusing of nonducted whistlers by the equatorial anomaly (1995)
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    Publication Date: 2019-07-13
    Description: Impulsive ELF/VLF electric field bursts observed by the vector electric field instrument (VEFI) on the Dynamics Explorer 2 (DE 2) satellite on almost every crossing of the geomagnetic equator in the evening hours are interpreted as originating in lightning discharges. These signals that peak in intensity near the magnetic equator are observed within 5-20 deg latitude of the geomagnetic equator at altitudes of 300-500 km with amplitudes of the order of approximately mV/m in the 512- or 1024-Hz frequency band of the VEFI instrument. Whistler-mode ELF/VLF wave propagation through a horizontally stratified ionosphere predicts strong attenuation of subionospheric signals reaching the equator at low altitudes. However, ray tracing analysis shows that the presence of the equatorial density anomaly, commonly observed in the upper ionosphere during evening hours, leads to the focusing of the wave energy from lightning near the geomagnetic equator at low altitudes, thus accounting for all observed aspects of the phenomenon. The observations presented here indicate that during certain hours in the evening, almost all the energy input from lightning discharges entering the ionosphere at less than 30 deg latitude remains confined to a small region (in altitude and latitude) near the geomagnetic equator. The net wideband electric field, extrapolated from the observed electric field values in the 512- to 1024-Hz band, can be approximately 10 mV/m or higher. These strong electric fields generated in the ionosphere by lightning at local evening times may be important for the equatorial electrodynamics of the ionosphere.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 100; A5; p. 7783-7790
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  • 4
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    Wave intensifications near the electron cyclotron frequency within the polar cusp (1990)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: As DE 1 flew through the polar cusp, enhanced narrowband electrostatic waves were sometimes observed just above the electron cyclotron frequency. Here, wave and particle measurements from three representative cusp transits are presented in order to characterize these signals and understand the conditions that favor their generation. It was found that the form of the local cusp electron velocity distribution had a direct influence on the wave spectral character. A preliminary study indicates that electron beams in the cusp can generate the enhanced signals, although generation by an anisotropic warm component cannot be ruled out.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 6493-650
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  • 5
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    Observations of the earth's polar cleft at large radial distances with the Hawkeye 1 magnetometer (1990)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Based on 364 spacecraft passes through the dayside region, the position of the polar cleft at large radial distances was determined with the magnetometer flown on Hawkeye 1. This data set is ideal for the study of the cusp and cleft region. Identification of the cleft depended on noting strong negative deviations of the magnetic field strength in the region from that of the dipole field. In solar magnetic coordinates, cleft observations were found between 40 deg and 70 deg latitude and + or - 75 deg latitude and + or - 75 deg longitude, while in geocentricmagnetospheric coordinates, these observations were found between 20 deg and 75 deg latitude and + or - 75 deg longitude. The extreme longitudinal extent of 150 deg is larger than those reported in some previous studies. Large magnetic depressions associated with the cleft extend out to 12 earth radii.
    Keywords: GEOPHYSICS
    Type: AD-A230791 , Journal of Geophysical Research (ISSN 0148-0227); 95; 20945-20
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  • 6
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    A statistical study of solar type III bursts and auroral kilometric radiation onsets (1985)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Simultaneous occurrences of type III solar radio bursts and auroral kilometric radiation were observed by Calvert (1981) using ISEE 1 spectrograms. Calvert presented evidence suggesting that the incoming type III burst stimulates the onset of auroral kilometric radiation (AKR). This paper presents a statistical study of the correlation between type III bursts and auroral kilometric radiation. A superposed epoch analysis was performed on as many as 186 type III events. The type III bursts were detected by the ISEE 3 spacecraft on the sunward side of the earth. At the same time the IMP 8 spacecraft was used to detect onsets of kilometric radiation on the nightside of the earth. For each event the intensities measured by ISEE 3 (type III intensities) were subtracted from the intensities measured by IMP 8 (type III and possible AKR intensities). The resulting intensities for each event were then added to determine if kilometric radiation was preferentially observed following a type III burst. This analysis was performed at frequencies of 100, 178, and 500 kHz. The results of this study show that a statistically significant correlation exists between incoming type III bursts from the sun and kilometric radiation from the earth.
    Keywords: GEOPHYSICS
    Type: AD-A162717 , Journal of Geophysical Research (ISSN 0148-0227); 90; 9634-964
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  • 7
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    AKR signal increases caused by triggering (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: This paper presents a study of the amplitude increases which accompany the triggering of auroral kilometric radiation (AKR) by type-III solar radio bursts. IMP-8 data were used to determine the signal increases observed during one-hour periods before and after type-III bursts at 100 kHz, 178 kHz, and 500 kHz, and these were compared with similar observations when the type-III bursts were absent. The results indicate that between 8 to 16 pct of the type-III bursts caused statistically significant intensity increases and that infrequent large signal increases of sometimes 20 dB or more tended to characterize the triggered AKR, rather than a large proportion of small increases.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 13; 370-372
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