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  • 1
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    Magnetosphere-ionosphere interactions (1979)
    In:  CASI
    Details
    Publication Date: 2006-01-16
    Description: The present understanding of magnetosphere ionosphere interactions is described, and present and future predictive capabilities are assessed. Ionospheric features directly coupled to the magnetosphere to a significant degree are considered, with emphasis given to those phenomena of major interest to forecasters and users.
    Keywords: GEOPHYSICS
    Type: NASA. Marshall Space Flight Center Solar-Terrest. Predictions Proc., Vol. 2; p 476-493
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  • 2
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    Inference of high-latitude ionization and conductivity from AE-C measurements of auroral electron fluxes (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Electron fluxes in the kilovolt energy range measured by the AE-C satellite have been used to infer the latitudinal distribution of ionization at high latitudes in the altitude range 90 to 200 km. These distributions are compared with simultaneous measurements of electron density by the Chatanika incoherent scatter radar. The study was based on more than 120 electron density profiles obtained on three different nights at magnetic local times between 0200 and 0400. The calculated distributions agree very well with the altitude and latitude distributions measured by the radar. The only obvious difference was the presence in the radar data of additional ionization produced by solar illumination. A comparison was also conducted of the height-integrated electrical conductivities computed from the measured profiles and those inferred from the satellite measurements. For Hall and Pedersen conductances greater than 5 mhos, the agreement is within 25 percent. The data were also used to deduce the altitude profile of the effective recombination coefficient. This profile agrees well with the results of previous studies.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 90; 7505-751
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  • 3
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    Auroral arc electrodynamic parameters measured by AE-C and the Chatanika radar (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Auroral arc electrodynamic parameters are studied using coordinated measurements between the AE-C satellite and the Chatanika radar. On January 4, 1978, the spacecraft twice crossed an east-west aligned auroral arc at widely spaced longitudes, spanning more than 3 hours in local time. The Chatanika radar was scanning in elevation at a magnetic longitude equidistant from the two AE-C crossings. The electric field pattern around this arc was remarkably similar at the three longitudes. Equatorward of the arc the north-south field was very intense (greater than approximately 60 mV/m), whereas poleward of the arc it was small (approximately 10 mV/m). The east-west field was small and almost constant across the arc. The same arc was observed by the radar for about 1 hour, and this electric field pattern did not change, even though the arc location, intensity, and width changed substantially. For a given electric field the AE-C measured ion temperature was substantially different during each of the arc crossings. This dissimilarity is attributed to differences in the F region neutral wind at the two longitudes. It is shown that the electric field variations are consistent with the existence of polarization charges within the arc, even though the electric field remained small poleward of the arc.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 86; June 1
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  • 4
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    Simultaneous rocket and radar measurements of currents in an auroral arc (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The data obtained by the vector magnetometer, the double probe, and the Chatanika radar used in a coordinated rocket and radar experiment in Alaska in March 1978 are analyzed. A brief description of the instruments is given, and the basic equations for the determination of ionospheric currents from electric field and conductivity measurements are reviewed. The results obtained by the three instruments are then compared and used to infer the nature of parallel and perpendicular current flow around the arc.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 86; Sept. 1
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  • 5
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    Mapping of auroral X-rays from rocket overflights (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Remote sensing of energetic auroral X-rays from above the emission region can provide both local and global information regarding X ray and energetic electron deposition within the middle atmosphere. However, contamination of X ray detectors by local corpuscular radiation can severely affect the scope and accuracy of the detector measurements. It is, therefore, necessary to employ techniques designed to observe X rays while rejecting the far more intense corpuscular radiation component. A suitable approach for the mapping of auroral X rays involves the employment of rockets for flights above the emission region. A description is presented of the results obtained from two rocket flights launched from Poker Flat Research Range, Alaska, during aurorally active periods in March 1978. The data were measured with the aid of scanning detectors protected from particles by broom magnet techniques.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 87; Apr. 1
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  • 6
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    Radar and photometric measurements of an intense type A red aurora (1985)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: On the evening of March 5, 1981, an intense, type A red aurora appeared over southern Alaska. Radar and photometric measurements were made of the aurora from the Chatanika radar site. The line of sight intensity of the 630.0-nm emissions exceeded 150 kR and was accompanied by enhanced emissions at 486.1 and 427.8 nm. The Chatanika radar measured electron densities of 10 to the 6th per cu cm and electron temperatures of 6000 K at an altitude of 400 km and an invariant latitude of 59 deg in association with the aurora. Comparison of optical and radar measurements indicated that the 630.0-nm emissions were produced to a large degree by thermal excitation of O(1D) in the region of high electron temperatures and densities. Model calculations indicate that the observed density and temperature enhancements and the related optical emissions were the results of a relatively short duration (5-10 min) pulse of precipitating, low-energy (about 30 eV) electrons. Whereas conventional stable auroral red arcs are associated with a gradual decrease in ring current energy density during the recovery phase of a magnetic storm, the type A red aurora may be produced by impulsive ring current energy loss during the main phase.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 90; 457-466
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  • 7
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    Model of Birkeland currents associated with an auroral arc (1975)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The ionospheric configuration of the vertical Birkeland currents associated with an auroral arc is calculated from a model based on the assumption that the auroral electrons constitute a net current into the ionosphere. It is further assumed that the return vertical current out of the ionosphere is impeded along the field lines which connect the arc to the magnetosphere. The magnitude, location, and structure of the return Birkeland current calculated from the model agree well with measurements of these parameters by a rocket-borne experiment.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 80; Oct. 1
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  • 8
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    Effect of anomalous transport coefficients on the thermal structure of the storm time auroral ionosphere (1978)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: By analyzing an observed storm time auroral electron temperature profile it is shown that anomalous transport effects strongly influence the thermal structure of the disturbed auroral ionosphere. Such anomalous transport effects are a consequence of plasma turbulence, the existence of which has been established by a large number of observations in the auroral ionosphere. The electron and composite ion energy equations are solved with anomalous electron thermal conductivity and parallel electrical resistivity coefficients. The solutions are parameterized with respect to a phenomenological altitude-dependent anomaly coefficient A and are compared with an observed storm time electron temperature profile above Chatanika. The calculated temperature profile for the classical case (A = 1) disagrees considerably with the measured profile over most of the altitude range up to 450 km. It is shown that an anomaly coefficient with a sharp peak of the order of 10,000 centered around the F2 peak is consistent with observations.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 83; Oct. 1
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  • 9
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    Observations of Birkeland currents at auroral latitudes (1975)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: After many years of languishing interest, field-aligned currents (Birkeland currents) are now regarded as an important link between the magnetosphere and the ionosphere. We describe techniques that are used to measure them and then discuss in some detail measurements that have been interpreted as indicating the presence of Birkeland currents. We conclude that measurements substantiate the theory of large-scale flow from the magnetosphere to the polar caps in a dawn-dusk direction with opposite flow equatorward of the auroral zone connecting to the Alfven layer. Sheet current flow in premidnight discrete aurora seems experimentally established also, but its connection with auroral acceleration and with the larger-scale flow is not yet understood. The currents flowing during a substorm are not yet fully defined either.
    Keywords: GEOPHYSICS
    Type: Reviews of Geophysics and Space Physics; 13; Feb. 197
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  • 10
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    Chatanika radar measurements of the electrical properties of auroral arcs (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Ionospheric parameters measured in the presence of auroral arcs by the incoherent scatter Chatanika radar are used to define properties of the arcs. The radar broadcasts at 3-5 MW with a range resolution of 4.5 km along the radar line-of-sight, and has yielded auroral measurements on the variation of electron density, Hall and Pederson conductivity, horizontal electric fields, electrojet currents, precipitating electron energy flux, and the Joule heating rate. Elevation-scan techniques have been utilized to study the latitude and altitude variation of the ionospheric plasma parameters, and fixed-position scans allow determination of ionization conditions, including the electric fields and the acceleration of precipitating auroral electrons. Arcs in the diffuse aurora have been found to be local conductivity enhancements, while discrete arcs correspond to the boundary plasma sheet and have an asymmetric electric field pattern reduced on the northward side.
    Keywords: GEOPHYSICS
    Type: Physics of auroral arc formation; Jul 21, 1980 - Jul 25, 1980; Fairbanks, AK
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