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  • 1
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    Online Resource
    Coordinated ground-based, low altitude satellite and Cluster observations on global and local scales during a transient post-noon sector excursion of the magnetospheric cusp
    Copernicus GmbH ; 2001
    In:  Annales Geophysicae Vol. 19, No. 10/12 ( 2001-09-30), p. 1367-1398
    Details
    In: Annales Geophysicae, Copernicus GmbH, Vol. 19, No. 10/12 ( 2001-09-30), p. 1367-1398
    Abstract: Abstract. On 14 January 2001, the four Cluster spacecraft passed through the northern magnetospheric mantle in close conjunction to the EISCAT Svalbard Radar (ESR) and approached the post-noon dayside magnetopause over Green-land between 13:00 and 14:00 UT. During that interval, a sudden reorganisation of the high-latitude dayside convection pattern occurred after 13:20 UT, most likely caused by a direction change of the Solar wind magnetic field. The result was an eastward and poleward directed flow-channel, as monitored by the SuperDARN radar network and also by arrays of ground-based magnetometers in Canada, Greenland and Scandinavia. After an initial eastward and later poleward expansion of the flow-channel between 13:20 and 13:40 UT, the four Cluster spacecraft, and the field line footprints covered by the eastward looking scan cycle of the Söndre Strömfjord incoherent scatter radar were engulfed by cusp-like precipitation with transient magnetic and electric field signatures. In addition, the EISCAT Svalbard Radar detected strong transient effects of the convection reorganisation, a poleward moving precipitation, and a fast ion flow-channel in association with the auroral structures that suddenly formed to the west and north of the radar. From a detailed analysis of the coordinated Cluster and ground-based data, it was found that this extraordinary transient convection pattern, indeed, had moved the cusp precipitation from its former pre-noon position into the late post-noon sector, allowing for the first and quite unexpected encounter of the cusp by the Cluster spacecraft. Our findings illustrate the large amplitude of cusp dynamics even in response to moderate solar wind forcing. The global ground-based data proves to be an invaluable tool to monitor the dynamics and width of the affected magnetospheric regions.Key words. Magnetospheric cusp, ionosphere, reconnection, convection flow-channel, Cluster, ground-based observations
    Type of Medium: Online Resource
    ISSN: 1432-0576
    URL: Article
    DOI: 10.5194/angeo-19-1367-2001
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2001
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  • 2
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    Density structures inside the plasmasphere: Cluster observations
    Copernicus GmbH ; 2004
    In:  Annales Geophysicae Vol. 22, No. 7 ( 2004-07-14), p. 2577-2585
    Details
    In: Annales Geophysicae, Copernicus GmbH, Vol. 22, No. 7 ( 2004-07-14), p. 2577-2585
    Abstract: Abstract. The electron density profiles derived from the EFW and WHISPER instruments on board the four Cluster spacecraft reveal density structures inside the plasmasphere and at its outer boundary, the plasmapause. We have conducted a statistical study to characterize these density structures. We focus on the plasmasphere crossing on 11 April 2002, during which Cluster observed several density irregularities inside the plasmasphere, as well as a plasmaspheric plume. We derive the density gradient vectors from simultaneous density measurements by the four spacecraft. We also determine the normal velocity of the boundaries of the plume and of the irregularities from the time delays between those boundaries in the four individual density profiles, assuming they are planar. These new observations yield novel insights about the occurrence of density irregularities, their geometry and their dynamics. These in-situ measurements are compared with global images of the plasmasphere from the EUV imager on board the IMAGE satellite.
    Type of Medium: Online Resource
    ISSN: 1432-0576
    URL: Article
    DOI: 10.5194/angeo-22-2577-2004
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2004
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  • 3
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    Online Resource
    Density irregularities in the plasmasphere boundary layer: Cluster observations in the dusk sector
    Elsevier BV ; 2005
    In:  Advances in Space Research Vol. 36, No. 10 ( 2005-1), p. 1964-1969
    Details
    In: Advances in Space Research, Elsevier BV, Vol. 36, No. 10 ( 2005-1), p. 1964-1969
    Type of Medium: Online Resource
    ISSN: 0273-1177
    URL: Article
    DOI: 10.1016/j.asr.2005.08.050
    Language: English
    Publisher: Elsevier BV
    Publication Date: 2005
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    SSG: 16,12
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  • 4
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    Online Resource
    A comparison of EISCAT and Dynasonde measurements of the auroral ionosphere
    Copernicus GmbH ; 1996
    In:  Annales Geophysicae Vol. 14, No. 12 ( 1996-12-31), p. 1403-1412
    Details
    In: Annales Geophysicae, Copernicus GmbH, Vol. 14, No. 12 ( 1996-12-31), p. 1403-1412
    Abstract: Abstract. Incoherent-scatter radar and ionospheric sounding are powerful and complementary techniques in the study of the Earth's ionosphere. The work presented here involves the use of the Tromsø Dynasonde as a correlative diagnostic with the EISCAT incoherent-scatter radar. A comparison of electron-density profiles shows how a Dynasonde can be used to calibrate an incoherent-scatter radar and to monitor changes in the system. Skymaps of the direction of Dynasonde echoes are compared with EISCAT-derived density profiles to illustrate how a Dynasonde can be used to measure the drift velocity of auroral features. Vector velocities fitted to Dynasonde echoes are compared with EISCAT-derived plasma velocities. The results show good agreement when the data are taken during quiet to moderately active conditions and averaged over time scales of 30 min or more.
    Type of Medium: Online Resource
    ISSN: 1432-0576
    URL: Article
    DOI: 10.1007/s00585-996-1403-x
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 1996
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  • 5
    Online Resource
    Online Resource
    Plasma drift estimates from the Dynasonde: comparison with EISCAT measurements
    Copernicus GmbH ; 1998
    In:  Annales Geophysicae Vol. 16, No. 10 ( 1998-10-31), p. 1138-1143
    Details
    In: Annales Geophysicae, Copernicus GmbH, Vol. 16, No. 10 ( 1998-10-31), p. 1138-1143
    Abstract: Abstract. Modern ionosondes make almost simultaneous measurements of the time rate of change of phase path in different directions and at different heights. By combining these 'Doppler' measurements and angles of arrival of many such radar echoes it is possible to derive reliable estimates of plasma drift velocity for a defined scattering volume. Results from both multifrequency and kinesonde-mode soundings at 3-min resolution show that the Dynasonde-derived F-region drift velocity is in good agreement with EISCAT, despite data loss during intervals of 'blanketing' by intense E-region ionisation. It is clear that the Tromsø Dynasonde, employing standard operating modes, gives a reliable indication of overall convection patterns during quiet to moderately active conditions.Key words. Auroral ionosphere · Plasma convection · Instruments and techniques
    Type of Medium: Online Resource
    ISSN: 1432-0576
    URL: Article
    DOI: 10.1007/s00585-998-1138-y
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 1998
    detail.hit.zdb_id: 1458425-6
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  • 6
    Online Resource
    Online Resource
    A comparison of EISCAT and Dynasonde measurements of the auroral ionosphere
    Copernicus GmbH ; 1996
    In:  Annales Geophysicae Vol. 14, No. 12 ( 1996), p. 1403-
    Details
    In: Annales Geophysicae, Copernicus GmbH, Vol. 14, No. 12 ( 1996), p. 1403-
    Type of Medium: Online Resource
    ISSN: 0992-7689
    URL: Article
    DOI: 10.1007/s005850050401
    Language: Unknown
    Publisher: Copernicus GmbH
    Publication Date: 1996
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    SSG: 16,13
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  • 7
    Online Resource
    Online Resource
    Ionospheric response to variable electric fields in small-scale auroral structures
    Copernicus GmbH ; 1998
    In:  Annales Geophysicae Vol. 16, No. 10 ( 1998-10-31), p. 1343-1354
    Details
    In: Annales Geophysicae, Copernicus GmbH, Vol. 16, No. 10 ( 1998-10-31), p. 1343-1354
    Abstract: Abstract. High time and space resolution optical and radar measurements have revealed the influence of electric fields on E-region electron density profiles in small-scale auroral structures. Large electric fields are present adjacent to auroral filaments produced by monoenergetic electron fluxes. The ionisation profiles measured within and beside the auroral filaments show the effects of plasma convection due to electric fields as well as the consequences of the response time to large and dynamic fluxes of energetic electrons. Without high-resolution optical measurements, the interpretation of the radar data is limited.Key words. Auroral ionosphere · Ionosphere-magnetosphere interactions · EISCAT
    Type of Medium: Online Resource
    ISSN: 1432-0576
    URL: Article
    DOI: 10.1007/s00585-998-1343-8
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 1998
    detail.hit.zdb_id: 1458425-6
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  • 8
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    Ohmic heating as evidence for strong field‐aligned currents in filamentary aurora
    American Geophysical Union (AGU) ; 2001
    In:  Journal of Geophysical Research: Space Physics Vol. 106, No. A2 ( 2001-02), p. 1785-1794
    Details
    In: Journal of Geophysical Research: Space Physics, American Geophysical Union (AGU), Vol. 106, No. A2 ( 2001-02), p. 1785-1794
    Abstract: A large increase in electron temperature measured in filamentary aurora with the European incoherent scatter radar has been modeled with a one‐dimensional electron transport and ion chemistry code. To account for the observed changes in electron temperature, while also reproducing the measured E region electron density profiles, a source of electron heating is required in addition to local heating from energy degradation of the precipitating electrons. We show that ohmic heating in a strong field‐aligned current can account for the required heat source.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/1999JA000292
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2001
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    detail.hit.zdb_id: 2220777-6
    detail.hit.zdb_id: 3094197-0
    SSG: 16,13
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  • 9
    Online Resource
    Online Resource
    Coherent EISCAT Svalbard Radar spectra from the dayside cusp/cleft and their implications for transient field‐aligned currents
    American Geophysical Union (AGU) ; 1999
    In:  Journal of Geophysical Research: Space Physics Vol. 104, No. A11 ( 1999-11), p. 24613-24624
    Details
    In: Journal of Geophysical Research: Space Physics, American Geophysical Union (AGU), Vol. 104, No. A11 ( 1999-11), p. 24613-24624
    Abstract: Naturally enhanced incoherent scatter spectra from the vicinity of the dayside cusp/cleft, interpreted as being due to plasma turbulence driven by short bursts of intense field‐aligned current, are compared with high‐resolution narrow‐angle auroral images and meridian scanning photometer data. Enhanced spectra have been observed on many occasions in association with nightside aurora, but there has been only one report of such spectra seen in the cusp/cleft region. Narrow‐angle images show considerable change in the aurora on timescales shorter than the 10‐s radar integration period, which could explain spectra observed with both ion lines simultaneously enhanced. Enhanced radar spectra are generally seen inside or beside regions of 630‐nm auroral emission, indicative of sharp F region conductivity gradients, but there appears also to be a correlation with dynamic, small‐scale auroral forms of order 100 m and less in width.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/1999JA900276
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1999
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    detail.hit.zdb_id: 161665-1
    detail.hit.zdb_id: 3094268-8
    detail.hit.zdb_id: 710256-2
    detail.hit.zdb_id: 2016804-4
    detail.hit.zdb_id: 3094181-7
    detail.hit.zdb_id: 3094219-6
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    detail.hit.zdb_id: 2220777-6
    detail.hit.zdb_id: 3094197-0
    SSG: 16,13
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  • 10
    Online Resource
    Online Resource
    Semiannual and annual variations in the height of the ionospheric F2-peak
    Copernicus GmbH ; 2000
    In:  Annales Geophysicae Vol. 18, No. 3 ( 2000-03-31), p. 285-299
    Details
    In: Annales Geophysicae, Copernicus GmbH, Vol. 18, No. 3 ( 2000-03-31), p. 285-299
    Abstract: Abstract. Ionosonde data from sixteen stations are used to study the semiannual and annual variations in the height of the ionospheric F2-peak, hmF2. The semiannual variation, which peaks shortly after equinox, has an amplitude of about 8 km at an average level of solar activity (10.7 cm flux = 140 units), both at noon and midnight. The annual variation has an amplitude of about 11 km at northern midlatitudes, peaking in early summer; and is larger at southern stations, where it peaks in late summer. Both annual and semiannual amplitudes increase with increasing solar activity by day, but not at night. The semiannual variation in hmF2 is unrelated to the semiannual variation of the peak electron density NmF2, and is not reproduced by the CTIP and TIME-GCM computational models of the quiet-day thermosphere and ionosphere. The semiannual variation in hmF2 is approximately "isobaric", in that its amplitude corresponds quite well to the semiannual variation in the height of fixed pressure-levels in the thermosphere, as represented by the MSIS empirical model. The annual variation is not "isobaric". The annual mean of hmF2 increases with solar 10.7 cm flux, both by night and by day, on average by about 0.45 km/flux unit, rather smaller than the corresponding increase of height of constant pressure-levels in the MSIS model. The discrepancy may be due to solar-cycle variations of thermospheric winds. Although geomagnetic activity, which affects thermospheric density and temperature and therefore hmF2 also, is greatest at the equinoxes, this seems to account for less than half the semiannual variation of hmF2. The rest may be due to a semiannual variation of tidal and wave energy transmitted to the thermosphere from lower levels in the atmosphere.Key words: Atmospheric composition and structure (thermosphere - composition and chemistry) - Ionosphere (mid-latitude ionosphere)
    Type of Medium: Online Resource
    ISSN: 1432-0576
    URL: Article
    DOI: 10.1007/s00585-000-0285-6
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2000
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