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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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    Paper (German National Licenses)
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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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    Paper (German National Licenses)
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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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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Probing discrete auroral arcs by ionospheric tomography (1998)
    Springer
    Annales geophysicae 16 (1998), S. 574-582 
    Details
    ISSN: 0992-7689
    Keywords: Ionosphere (Auroral ionosphere) ; Magnetospheric physics (Auroral phenomena) ; Radio science (Ionospheric physics)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Optical observations of 557.7 nm and 630.0 nm emissions from discrete auroral arcs in the post-noon sector have been related to localised field-aligned enhancements in the spatial distribution of E- and F-layer electron density respectively seen in images reconstructed by ionospheric tomography. Results from two case studies are presented in which meridian scanning photometer and all-sky camera observations on Svalbard have been compared to electron-density structures found by tomographic inversion of measurements made by reception of radio signals at a chain of four stations at high latitude. The F-layer features are long-lived and show exact correspondence to the red-line emissions. Transient arcs in green-line intensity result in E-region structures that are resolved in one case, but not in another where the dynamic auroral forms are separated by less than one degree of latitude. The signature of an inverted-V precipitation event is clearly evident in one example.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-998-0574-z
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  • 5
    Electronic Resource
    Electronic Resource
    Structure of the poleward wall of the trough and the inclination of the geomagnetic field above the EISCAT radar (1997)
    Springer
    Annales geophysicae 15 (1997), S. 740-746 
    Details
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A special high-resolution routine of the EISCAT radar has been used to investigate the structure and development of the poleward wall of a deep trough in electron density. The feature was tracked by the radar during a 7-hour period under very quiet geomagnetic conditions. The field-aligned nature of the structure enabled an estimate to be made of the inclination of the geomagnetic field above EISCAT that was in good agreement with the current model. Observations of narrow field-aligned enhancements in electron temperature demonstrated that the wall of this trough is a dynamic feature, reforming regularly as the electron density responds on a time scale of tens of minutes to energy input from soft-particle precipitation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-997-0740-8
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    Paper (German National Licenses)
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  • 6
    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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  • 7
    Electronic Resource
    Electronic Resource
    On the possible role of cusp/cleft precipitation in the formation of polar-cap patches (1999)
    Springer
    Annales geophysicae 17 (1999), S. 1298-1305 
    Details
    ISSN: 0992-7689
    Keywords: Ionosphere (ionospheric irregularities; particle precipitation; polar ionosphere)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The work describes experimental observations of enhancements in the electron density of the ionospheric F-region created by cusp/cleft particle precipitation at the dayside entry to the polar-cap convection flow. Measurements by meridian scanning photometer and all-sky camera of optical red-line emissions from aurora are used to identify latitudinally narrow bands of soft-particle precipitation responsible for structured enhancements in electron density determined from images obtained by radio tomography. Two examples are discussed in which the electron density features with size scales and magnitudes commensurate with those of patches are shown to be formed by precipitation at the entry region to the anti-sunward flow. In one case the spectrum of the incoming particles results in ionisation being created, for the most part below 250 km, so that the patch will persist only for minutes after convecting away from the auroral source region. However in a second example, at a time when the plasma density of the solar wind was particularly high, a substantial part of the particle-induced enhancement formed above 250 km. It is suggested that, with the reduced recombination loss in the upper F-region, this structure will retain form as a patch during passage in the anti-sunward flow across the polar cap.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-999-1298-4
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  • 8
    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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    Paper (German National Licenses)
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  • 9
    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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  • 10
    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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