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  • Springer  (4)
  • Potsdam : GeoForschungsZentrum
  • 1995-1999  (4)
  • 1997  (4)
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  • 1995-1999  (4)
Year
  • 1
    Electronic Resource
    Electronic Resource
    CUTLASS/IMAGE observations of high-latitude convection features during substorms (1997)
    Springer
    Annales geophysicae 15 (1997), S. 692-702 
    Details
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The CUTLASS Finland HF radar has been operational since February 1995. The radar frequently observes backscatter during the midnight sector from a latitude range 70–75° geographic, latitudes often associated with the polar cap. These intervals of backscatter occur during intervals of substorm activity, predominantly in periods of relatively quiet magnetospheric activity, with Kp during the interval under study being 2-and ∑KP for the day being only 8-. During August 1995 the radar ran in a high time resolution mode, allowing measurements of line-of-sight convection velocities along a single beam with a temporal resolution of 14s, and measurement of a full spatial scan of line-of-sight convection velocities every four minutes. Data from such scans reveal the radar to be measuring return flow convection during the interval of substorm activity. For three intervals during the period under study, a reduction in the spatial extent of radar backscatter occurred. This is a consequence of D region HF absorption and its limited extent in the present study is probably a consequence of the high latitude of the substorm activity, with the electrojet centre lying between 67° and 71° geomagnetic latitude. The high time resolution beam of the radar additionally demonstrates that the convection is highly time dependent. Pulses of equatorward flow exceeding ∼600 m s−1 are observed with a duration of ∼5 min and a repetition period of ∼8 min. Their spatial extent in the CUTLASS field of view was 400–500 km in longitude, and 300–400 km in latitude. Each pulse of enhanced equatorward flow was preceded by an interval of suppressed flow and enhanced ionospheric Hall conductance. The transient features are interpreted as being due to ionospheric current vortices associated with field aligned current pairs. The relationship between these observations and substorm phenomena in the magnetotail is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-997-0692-z
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  • 2
    Electronic Resource
    Electronic Resource
    The response of the magnetosphere to the passage of a coronal mass ejection on March 20–21 1990 (1997)
    Springer
    Annales geophysicae 15 (1997), S. 671-684 
    Details
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The geomagnetic response to the passage of a coronal mass ejection (CME) is studied. The passage of the CME resulted in a storm sudden commencement (SSC) at 2243 UT on March 20 1990 with disturbed magnetic activity during the following 24 h. The auroral, sub-auroral and equatorial magnetic response to the southward turning at 1314 (±5) UT on March 21 and the equatorial response to the southward turning associated with the SSC on 20 March are discussed in terms of existing models. It is found that the auroral and sub-auroral response to the southward turning associated with the SSC is a factor 2 or more quicker than normal due to the shock in the solar wind dynamic pressure. The low-latitude response time to the south-ward turning, characterised by Dst and the magneto-pause current corrected Dst*, is una.ected by the shock. Dst and Dst*, characteristic of the equatorial magnetic field, responded to the 1314 (±5) UT southward turning prior to the first observed substorm expansion phase onset, suggesting that a dayside loading process was responsible for the initial enhancement in the ring current rather than nightside particle injection. The response time of the auroral and sub-auroral magnetic field to the southward turning at 1314 (±5) UT on March 21 is measured at a variety of longitudes and latitudes. The azimuthal propagation velocity of the response to the southward turning varied considerably with latitude, ranging from #x0223C;8 km s−1 at 67°N to ∼4 kms−1 at 55°N. The southward velocity of the equatorward boundary of the northern polar convection pattern has been measured. This velocity was ∼1.2 km s−1 at 1600 MLT, although there was evidence that this may vary at different local times.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-997-0671-4
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  • 3
    Electronic Resource
    Electronic Resource
    Upstream waves and field line resonances: simultaneous presence and alternation in Pc3 pulsation events (1997)
    Springer
    Annales geophysicae 16 (1997), S. 34-48 
    Details
    ISSN: 0992-7689
    Keywords: Magnetosphere Physics ; MHD waves and instabilities ; Plasmasphere/Solar wind ; magnetosphere interactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Based on a detailed study of Pc3 events at an array between L = 1.5 and 3 in Central Europe, the authors found quick changes between upstream waves (UW, i.e. pulsation directly driven by UW) and field line resonance (FLR, i.e. azimuthal oscillations of geomagnetic field lines). The alternation of the two types is especially characteristic (and the UW part stronger) if the interplanetary magnetic field (IMF) is highly variable. Events due to field line resonance may have a structure consisting of multiple lines with frequencies differing by about 10%, corresponding to neighbouring shells of field lines separated by about 100 km at the surface. This coincides with previous findings (about 10% at a meridional distance of 80 km). The frequency of the UW type is well correlated with the frequency of waves in the interplanetary medium. Additionally, there are signals of unidentified origin which also seem to be influenced by IMF.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-997-0034-1
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  • 4
    Electronic Resource
    Electronic Resource
    THE CLUSTER MAGNETIC FIELD INVESTIGATION (1997)
    Springer
    Space science reviews 79 (1997), S. 65-91 
    Details
    ISSN: 1572-9672
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The Cluster mission provides a new opportunity to study plasma processes and structures in the near-Earth plasma environment. Four-point measurements of the magnetic field will enable the analysis of the three dimensional structure and dynamics of a range of phenomena which shape the macroscopic properties of the magnetosphere. Difference measurements of the magnetic field data will be combined to derive a range of parameters, such as the current density vector, wave vectors, and discontinuity normals and curvatures, using classical time series analysis techniques iteratively with physical models and simulation of the phenomena encountered along the Cluster orbit. The control and understanding of error sources which affect the four-point measurements are integral parts of the analysis techniques to be used. The flight instrumentation consists of two, tri-axial fluxgate magnetometers and an on-board data-processing unit on each spacecraft, built using a highly fault-tolerant architecture. High vector sample rates (up to 67 vectors s-1) at high resolution (up to 8 pT) are combined with on-board event detection software and a burst memory to capture the signature of a range of dynamic phenomena. Data-processing plans are designed to ensure rapid dissemination of magnetic-field data to underpin the collaborative analysis of magnetospheric phenomena encountered by Cluster.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004970907748
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