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  • Ionosphere (auroral ionosphere)  (2)
  • Ionosphere (auroral ionosphere; electric fields and currents)  (2)
  • Ionosphere (Auroral ionosphere)  (1)
  • Ionosphere (auroral ionosphere; ionosphere-magnetosphere interactions)  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Combined CUTLASS, EISCAT and ESR observations of ionospheric plasma flows at the onset of an isolated substorm (2000)
    Springer
    Annales geophysicae 18 (2000), S. 1073-1087 
    Details
    ISSN: 0992-7689
    Keywords: Ionosphere (auroral ionosphere) ; Magnetospheric physics (magnetosphere – ionosphere interactions; storms and substorms)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract On August 21st 1998, a sharp southward turning of the IMF, following on from a 20 h period of northward directed magnetic field, resulted in an isolated substorm over northern Scandinavia and Svalbard. A combination of high time resolution and large spatial scale measurements from an array of coherent scatter and incoherent scatter ionospheric radars, ground magnetometers and the Polar UVI imager has allowed the electrodynamics of the impulsive substorm electrojet region during its first few minutes of evolution at the expansion phase onset to be studied in great detail. At the expansion phase onset the substorm onset region is characterised by a strong enhancement of the electron temperature and UV aurora. This poleward expanding auroral structure moves initially at 0.9 km s-1 poleward, finally reaching a latitude of 72.5°. The optical signature expands rapidly westwards at ~6 km s-1, whilst the eastward edge also expands eastward at ~0.6 km s-1. Typical flows of 600 m s-1 and conductances of 2 S were measured before the auroral activation, which rapidly changed to ~100 m s-1 and 10–20 S respectively at activation. The initial flow response to the substorm expansion phase onset is a flow suppression, observed up to some 300 km poleward of the initial region of auroral luminosity, imposed over a time scale of less than 10 s. The high conductivity region of the electrojet acts as an obstacle to the flow, resulting in a region of low-electric field, but also low conductivity poleward of the high-conductivity region. Rapid flows are observed at the edge of the high-conductivity region, and subsequently the high flow region develops, flowing around the expanding auroral feature in a direction determined by the flow pattern prevailing before the substorm intensification. The enhanced electron temperatures associated with the substorm-disturbed region extended some 2° further poleward than the UV auroral signature associated with it.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-000-1073-z
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Multi-instrument observations of the electric and magnetic field structure of omega bands (1999)
    Springer
    Annales geophysicae 18 (1999), S. 99-110 
    Details
    ISSN: 0992-7689
    Keywords: Ionosphere (auroral ionosphere; electric fields and currents) ; Magnetospheric physics (magnetosphere-ionosphere interactions)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract High time resolution data from the CUTLASS Finland radar during the interval 01:30–03:30 UT on 11 May, 1998, are employed to characterise the ionospheric electric field due to a series of omega bands extending ∼5° in latitude at a resolution of 45 km in the meridional direction and 50 km in the azimuthal direction. E-region observations from the STARE Norway VHF radar operating at a resolution of 15 km over a comparable region are also incorporated. These data are combined with ground magnetometer observations from several stations. This allows the study of the ionospheric equivalent current signatures and height integrated ionospheric conductances associated with omega bands as they propagate through the field-of-view of the CUTLASS and STARE radars. The high-time resolution and multi-point nature of the observations leads to a refinement of the previous models of omega band structure. The omega bands observed during this interval have scale sizes ∼500 km and an eastward propagation velocity ∼0.75 km s−1. They occur in the morning sector (∼05 MLT), simultaneously with the onset/intensification of a substorm to the west during the recovery phase of a previous substorm in the Scandinavian sector. A possible mechanism for omega band formation and their relationship to the substorm phase is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-000-0099-6
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    SuperDARN studies of the ionospheric convection response to a northward turning of the interplanetary magnetic field (1998)
    Springer
    Annales geophysicae 16 (1998), S. 549-565 
    Details
    ISSN: 0992-7689
    Keywords: Ionosphere (Auroral ionosphere) ; Magnetospheric physics (Magnetopause, cusp, and boundary layers; Magnetosphere-ionosphere interaction)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The response of the dayside ionospheric flow to a sharp change in the direction of the interplanetary magnetic field (IMF) measured by the WIND spacecraft from negative Bz and positive By, to positive Bz and small By, has been studied using SuperDARN radar, DMSP satellite, and ground magnetometer data. In response to the IMF change, the flow underwent a transition from a distorted twin-cell flow involving antisunward flow over the polar cap, to a multi-cell flow involving a region of sunward flow at high latitudes near noon. The radar data have been studied at the highest time resolution available (∼2 min) to determine how this transition took place. It is found that the dayside flow responded promptly to the change in the IMF, with changes in radar and magnetic data starting within a few minutes of the estimated time at which the effects could first have reached the dayside ionosphere. The data also indicate that sunward flows appeared promptly at the start of the flow change (within ∼2 min), localised initially in a small region near noon at the equatorward edge of the radar backscatter band. Subsequently the region occupied by these flows expanded rapidly east-west and poleward, over intervals of ∼7 and ∼14 min respectively, to cover a region at least 2 h wide in local time and 5° in latitude, before rapid evolution ceased in the noon sector. In the lower latitude dusk sector the evolution extended for a further ∼6 min before quasi-steady conditions again prevailed within the field-of-view. Overall, these observations are shown to be in close conformity with expectations based on prior theoretical discussion, except for the very prompt appearance of sunward flows after the onset of the flow change.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-998-0549-0
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    CUTLASS HF radar observations of high-latitude azimuthally propagating vortical currents in the nightside ionosphere during magnetospheric substorms (2000)
    Springer
    Annales geophysicae 18 (2000), S. 640-652 
    Details
    ISSN: 0992-7689
    Keywords: Ionosphere (auroral ionosphere; electric fields and currents) ; Magnetospheric physics (storms and substorms)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract High-time resolution CUTLASS observations and ground-based magnetometers have been employed to study the occurrence of vortical flow structures propagating through the high-latitude ionosphere during magnetospheric substorms. Fast-moving flow vortices (∼800 m s−1) associated with Hall currents flowing around upward directed field-aligned currents are frequently observed propagating at high speed (∼1 km s−1) azimuthally away from the region of the ionosphere associated with the location of the substorm expansion phase onset. Furthermore, a statistical analysis drawn from over 1000 h of high-time resolution, nightside radar data has enabled the characterisation of the bulk properties of these vortical flow systems. Their occurrence with respect to substorm phase has been investigated and a possible generation mechanism has been suggested.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-000-0640-7
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    High-latitude HF Doppler observations of ULF waves: 2. Waves with small spatial scale sizes (1999)
    Springer
    Annales geophysicae 17 (1999), S. 868-876 
    Details
    ISSN: 0992-7689
    Keywords: Ionosphere (auroral ionosphere; ionosphere-magnetosphere interactions) ; Magnetospheric physics (MHD waves and instabilities)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The DOPE (Doppler Pulsation Experiment) HF Doppler sounder located near Tromsø, Norway (geographic: 69.6°N 19.2°E; L = 6.3) is deployed to observe signatures, in the high-latitude ionosphere, of magnetospheric ULF waves. A type of wave has been identified which exhibits no simultaneous ground magnetic signature. They can be subdivided into two classes which occur in the dawn and dusk local time sectors respectively. They generally have frequencies greater than the resonance fundamentals of local field lines. It is suggested that these may be the signatures of high-m ULF waves where the ground magnetic signature has been strongly attenuated as a result of the scale size of the waves. The dawn population demonstrate similarities to a type of magnetospheric wave known as giant (Pg) pulsations which tend to be resonant at higher harmonics on magnetic field lines. In contrast, the waves occurring in the dusk sector are believed to be related to the storm-time Pc5s previously reported in VHF radar data. Dst measurements support these observations by indicating that the dawn and dusk classes of waves occur respectively during geomagnetically quiet and more active intervals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-999-0868-9
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Interhemispheric observations of nightside ionospheric electric fields in response to IMF Bz and By changes and substorm pseudobreakup (2000)
    Springer
    Annales geophysicae 18 (2000), S. 897-907 
    Details
    ISSN: 0992-7689
    Keywords: Ionosphere (auroral ionosphere) ; Magnetospheric physics (magnetosphere-ionosphere interactions; storms and substorms)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract HF radar data during equinoctial, small IMF By conditions have enabled the ionospheric convection during the substorm growth phase and substorm pseudobreakup to be studied in both hemispheres. This has revealed both conjugate and non-conjugate convection behaviour during the substorm growth phase before and after the pseudobreakup onset. The nightside convection pattern is found to respond promptly to the southward turning of the interplanetary magnetic field (IMF) which impacts on the dusk flank of the magnetosphere due to an inclined phase front in the IMF in the case study presented. The subsequent interhemispheric observations of nightside convection are controlled by the IMF By polarity. The time scale for the response to changes in the IMF By component is found to be a little longer than for Bz, and the full impact of the IMF By is not apparent in the nightside convection until after substorm pseudobreakup has occurred. The pseudobreakup itself is found to result in a transitory suppression in the ionospheric electric field in both hemispheres. This flow suppression is very similar to that observed in HF radar observations of full substorm onset, with the exception of a lack of subsequent poleward expansion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-000-0897-x
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    Paper (German National Licenses)
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