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  • 1
    Electronic Resource
    Electronic Resource
    Dayside ionospheric response to changes in IMF polarity: optical and plasma-flow observations (2000)
    Springer
    Annales geophysicae 18 (2000), S. 782-788 
    Details
    ISSN: 0992-7689
    Keywords: Ionosphere (ionosphere-magnetosphere interactions) ; Magnetospheric physics (magnetosphere-ionosphere interactions; polar cap phenomena)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The response of the dayside ionosphere to changes in polarity of the interplanetary magnetic field was observed by two independent techniques. The signatures were seen in the 630.0 nm red-line emission, measured by a meridian scanning photometer at Ny-Ålesund on Svalbard, and also in the line-of-sight plasma velocities monitored by the Finland CUTLASS SuperDARN radar. A time difference of some 6 to 8 min occurred between the responses of the two techniques, with the flows being first to respond. In the present case study, the longer delay in the optics suggests that ion precipitation controls the auroral emission.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-000-0782-7
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  • 2
    Electronic Resource
    Electronic Resource
    Multi-instrument probing of the polar ionosphere under steady northward IMF (1999)
    Springer
    Annales geophysicae 18 (1999), S. 90-98 
    Details
    ISSN: 0992-7689
    Keywords: Ionosphere (polar ionosphere) ; Magnetospheric physics (magnetosphere-ionosphere interactions; polar cap phenomena)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Observations are presented of the polar ionosphere under steady, northward IMF. The measurements, made by six complementary experimental techniques, including radio tomography, all-sky and meridian scanning photometer optical imaging, incoherent and coherent scatter radars and satellite particle detection, reveal plasma parameters consistent with ionospheric signatures of lobe reconnection. The optical green-line footprint of the reconnection site is seen to lie in the sunward plasma convection of the lobe cells. Downstream in the region of softer precipitation the reverse energy dispersion of the incoming ions can be identified. A steep latitudinal density gradient at the equatorward edge of the precipitation identifies the general location of an adiaroic boundary, separating the open field lines of polar lobe cells from the closed field of viscous-driven cells. Enhancements in plasma density to the south of the gradient are interpreted as ionisation being reconfigured as it is thrust against the boundary by the antisunward flow of the viscous cells near noon. Each of the instruments individually provides valuable information on certain aspects of the ionosphere, but the paper demonstrates that taken together the different experiments complement each other to give a consistent and comprehensive picture of the dayside polar ionosphere.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-000-0090-2
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  • 3
    Electronic Resource
    Electronic Resource
    Determination of the vertical electron-density profile in ionospheric tomography: experimental results (1997)
    Springer
    Annales geophysicae 15 (1997), S. 747-752 
    Details
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The reconstruction of the vertical electron-density profile is a fundamental problem in ionospheric tomography. Lack of near-horizontal ray paths limits the information available on the vertical profile, so that the resultant image of electron density is biased in a horizontal sense. The vertical profile is of great importance as it affects the authenticity of the entire tomographic image. A new method is described whereby the vertical profile is selected using relative total-electron-content measurements. The new reconstruction process has been developed from modelling studies. A range of background ionospheres, representing many possible peak heights, scale heights and electron densities are formed from a Chapman profile on the bottomside with a range of topside profiles. The iterative reconstruction process is performed on all of these background ionospheres and a numerical selection criterion employed to select the final image. The resulting tomographic images show excellent agreement in electron density when compared with independent verification provided by the EISCAT radar.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-997-0747-1
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  • 4
    Electronic Resource
    Electronic Resource
    First complementary observations by ionospheric tomography, the EISCAT Svalbard radar and the CUTLASS HF radar (1998)
    Springer
    Annales geophysicae 16 (1998), S. 1519-1522 
    Details
    ISSN: 0992-7689
    Keywords: Ionosphere ; Auroral ionosphere ; Polar ionosphere ; Radio science (ionospheric physics)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Experimental results are presented from ionospheric tomography, the EISCAT Svalbard radar and the CUTLASS HF radar. Tomographic measurements on 10 October 1996, showing a narrow, field-aligned enhancement in electron density in the post-noon sector of the dayside auroral zone, are related to a temporal increase in the plasma concentration observed by the incoherent scatter radar in the region where the HF radar indicated a low velocity sunwards convection. The results demonstrate the complementary nature of these three instruments for polar-cap ionospheric studies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-998-1519-2
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  • 5
    Electronic Resource
    Electronic Resource
    The spatial structure of the dayside ionospheric trough (1998)
    Springer
    Annales geophysicae 16 (1998), S. 1169-1179 
    Details
    ISSN: 0992-7689
    Keywords: Ionosphere-magnetosphere interactions ; Polar ionosphere ; Radio science ; Ionospheric propagation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Tomographic imaging provides a powerful technique for obtaining images of the spatial distribution of ionospheric electron density at polar latitudes. The method, which involves monitoring radio transmissions from the Navy Navigation Satellite System at a meridional chain of ground receivers, has particular potential for complementing temporal measurements by other observing techniques such as the EISCAT incoherent-scatter radar facility. Tomographic reconstructions are presented here from a two-week campaign in November 1995 that show large-scale structuring of the polar ionosphere. Measurements by the EISCAT radar confirm the authenticity of the technique and provide additional information of the plasma electron and ion temperatures. The dayside trough, persistently observed at high latitudes during a geomagnetically quiet period but migrating to lower latitudes with increasing activity, is discussed in relationship to the pattern of the polarcap convection.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-998-1169-4
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  • 6
    Electronic Resource
    Electronic Resource
    EISCAT verification in the development of ionospheric tomography (1997)
    Springer
    Annales geophysicae 14 (1997), S. 1413-1421 
    Details
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract This paper highlights the important role played by the EISCAT radar for verification in the development of tomographic techniques to produce images of ionospheric electron density. A brief review is given of some of the stages in the application of tomographic reconstruction techniques to the ionosphere. Results are presented to illustrate the effectiveness of the method in imaging ionospheric structures at high latitudes. In addition, the results include the first tomographic image of the ionosphere for a region extending from mid-latitudes over mainland Scandinavia to high latitudes above Svalbard.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-996-1413-8
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  • 7
    Electronic Resource
    Electronic Resource
    Multi-instrument study of footprints of magnetopause reconnection in the summer ionosphere (2000)
    Springer
    Annales geophysicae 18 (2000), S. 1118-1127 
    Details
    ISSN: 0992-7689
    Keywords: Ionosphere (ionosphere-magnetosphere interactions; particle precipitation; plasma temperature and density)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Results are presented from a multi-instrument investigation of the signatures of equatorial reconnection in the summer, sunlit ionosphere. Well-established ion dispersion signatures measured during three DMSP satellite passes were used to identify footprints in ionospheric observations made by radio tomography, and both the EISCAT ESR and mainland radars. Under the prevalent conditions of southward IMF with the Bz component increasing in magnitude, the reconnection footprint was seen to move equatorward through the ESR field-of-view. The most striking signature was in the electron temperatures of the F2 region measured by the EISCAT mainland radar that revealed significantly enhanced temperatures with a steep equatorward edge, in general agreement with the leading edge of the ion dispersion. It is suggested that this sharp transition in the electron temperature may be an indicator of the boundary, mapping from the reconnection site, between closed geomagnetic field lines and those opened along which magnetosheath ions precipitate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-000-1118-3
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  • 8
    Electronic Resource
    Electronic Resource
    Polar patches observed by ESR and their possible origin in the cusp region (2000)
    Springer
    Annales geophysicae 18 (2000), S. 1043-1053 
    Details
    ISSN: 0992-7689
    Keywords: Ionosphere (ionosphere–magnetosphere interactions; plasma temperature and density; polar ionosphere)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Observations by the EISCAT Svalbard radar in summer have revealed electron density enhancements in the magnetic noon sector under conditions of IMF Bz southward. The features were identified as possible candidates for polar-cap patches drifting anti-Sunward with the plasma flow. Supporting measurements by the EISCAT mainland radar, the CUTLASS radar and DMSP satellites, in a multi-instrument study, suggested that the origin of the structures lay upstream at lower latitudes, with the modulation in density being attributed to variability in soft-particle precipitation in the cusp region. It is proposed that the variations in precipitation may be linked to changes in the location of the reconnection site at the magnetopause, which in turn results in changes in the energy distribution of the precipitating particles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-000-1043-5
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  • 9
    Electronic Resource
    Electronic Resource
    Two-dimensional mapping of the plasma density in the upper atmosphere with computerized ionospheric tomography (CIT) : The 39th annual meeting of division of plasma physics of APS (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 2010-2021 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Tomographic imaging of the ionosphere is a recently developed technique that uses integrated measurements and computer reconstructions to determine electron densities. The integral of electron density along vertical or oblique paths is obtained with radio transmissions from low-earth-orbiting (LEO) satellite transmitters to a chain of receivers on the earth's surface. Similar measurements along horizontal paths can be made using transmissions from Global Position System (GPS) navigation satellites to GPS receivers on LEO spacecraft. Also, the intensities of extreme ultraviolet (EUV) emissions can be measured with orbiting spectrometers. These intensities are directly related to the integral of the oxygen ion and electron densities along the instrument line of sight. Two-dimensional maps of the ionospheric plasma are produced by analyzing the combined radio and EUV data using computerized ionospheric tomography (CIT). Difficulties associated with CIT arise from the nonuniqueness of the reconstructions, owing to limited angle measurements or nonoptimal receiver location. Improvements in both reconstruction algorithms and CIT measurement systems are being implemented to overcome these difficulties. New imaging systems being developed employ CIT for large area mapping of the plasma densities in the ionosphere. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872872
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