Space Science Centre
Centre de recherche public Accréditation CIR
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Téléphone : 44 (0)1273 678 407
Mail : pg.enquiries [ at ] sussex.ac.uk
Adresse :
School of Engineering & Design, Engineering-2 Building
University of Sussex
BN1 9QT Brighton
Royaume-Uni
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Description
(Extrait du site web) |
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The Space Science Centre is actively involved with international space missions:
European Space Agency Cluster II, Chinese Double Star Probe, International Space Station, Space Shuttle flights STS-46, STS75. Research in the Sussex Space Science Centre embraces a variety of topics: - Information Technology, - Space Science, - Space Instrumentation, - Computer Simulations, - Geophysics and Plasma Theory: |
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Profil scientifique partiel |
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Domaines étudiés partiels
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Domaines scientifiques
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Quelques documents de Space Science Centre
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Instantaneous local wave vector estimation from multi-spacecraft measurements using few spatial points
Auteurs :
A.M. Buckley, T.D. Carozzi et M.P. Gough
Masquer le résumé
We introduce a technique to determine instantaneous local properties of waves based on discrete-time sampled, real-valued measurements from 4 or more spatial points. The technique is a generalisation to the spatial domain of the notion of instantaneous frequency used in signal processing. The quantities derived by our technique are closely related to those used in geometrical optics, namely the local wave vector and instantaneous phase velocity. Thus, this experimental technique complements ray-tracing. We provide example applications of the technique to electric field and potential data from the EFW instrument on Cluster. Cluster is the first space mission for which direct determination of the full 3-dimensional local wave vector is possible, as described here.
Storm time changes in total electron content in ionosphere measured by low orbiting topside sounder
Auteurs :
H. Alleyne, I. Bates, N. Beloff, P.F. Denisenko, M.P. Gough, I.I. Ivanov, S.I. Klimov, O.A. Maltseva et M.N. Nozdrachev
Masquer le résumé
A new experimental technique is presented for the determination of the total electron content (TEC) below a low-orbiting satellite. According to this technique TEC can be obtained using the segment of a topside ionogram that only contains the traces of signals reflected from the Earth's surface. Possibilities of this technique were demonstrated using MIR station topside sounding data at the night time for both quiet and disturbed ionospheric conditions, and in particular, during the 14 November 1998 storm. An interesting fact was revealed with the help of this technique: after a series of relatively strong storms the main ionospheric trough on 14 November 1998 was detected at an abnormally low geomagnetic latitude (~43°). During this study some spatial variations of TEC were registered that can be interpreted as a TID-type wave structure.
Instantaneous local wave vector estimation from multi-spacecraft measurements using few spatial points
Auteurs :
A.M. Buckley, T.D. Carozzi et M.P. Gough
Masquer le résumé
We introduce a technique to determine instantaneous local properties of waves based on discrete-time sampled, real-valued measurements from 4 or more spatial points. The technique is a generalisation to the spatial domain of the notion of instantaneous frequency used in signal processing. The quantities derived by our technique are closely related to those used in geometrical optics, namely the local wave vector and instantaneous phase velocity. Thus, this experimental technique complements ray-tracing. We provide example applications of the technique to electric field and potential data from the EFW instrument on Cluster. Cluster is the first space mission for which direct determination of the full 3-dimensional local wave vector is possible, as described here.
Coordinated Cluster and ground-based instrument observations of transient changes in the magnetopause boundary layer during an interval of predominantly northward IMF: relation to reconnection pulses and FTE signatures
Auteurs :
D. Alcaydé, O. Amm, A. Balogh, R. Behlke, P.L. Blelly, J.M. Bosqued, C. Cully, W.F. Denig, E.F. Donovan, M.W. Dunlop, P. Eglitis, M.J. Engebretson, A.N. Fazakerley, H. Frey, R. Greenwald, T.L. Hansen, M.A. Hapgood, K. Kauristie, M. Lester, M. Lockwood, G. Lu, M.F. Marcucci, I.W. Mccrea, J. Moen, S.K. Morley, H.J. Opgenoorth, F. Pitout, P. Prikryl, G. Provan, T.I. Pulkkinen, Henri Rème, R. Stamper, A. Strømme, M.G.G.T. Taylor, A.P. Van Eyken, J. Waterman, M.N. Wild et J.A. Wild
Masquer le résumé
We study a series of transient entries into the low-latitude boundary layer (LLBL) of all four Cluster spacecraft during an outbound pass through the mid-afternoon magnetopause ( [ XGSM, YGSM, ZGSM ] ˜ [ 2, 7, 9 ] R E ). The events take place during an interval of northward IMF, as seen in the data from the ACE satellite and lagged by a propagation delay of 75 min that is welldefined by two separate studies: (1) the magnetospheric variations prior to the northward turning (Lockwood et al., 2001, this issue) and (2) the field clock angle seen by Cluster after it had emerged into the magnetosheath (Opgenoorth et al., 2001, this issue). With an additional lag of 16.5 min, the transient LLBL events correlate well with swings of the IMF clock angle (in GSM) to near 90°. Most of this additional lag is explained by ground-based observations, which reveal signatures of transient reconnection in the pre-noon sector that then take 10–15 min to propagate eastward to 15 MLT, where they are observed by Cluster. The eastward phase speed of these signatures agrees very well with the motion deduced by the cross-correlation of the signatures seen on the four Cluster spacecraft. The evidence that these events are reconnection pulses includes: transient erosion of the noon 630 nm (cusp/cleft) aurora to lower latitudes; transient and travelling enhancements of the flow into the polar cap, imaged by the AMIE technique; and poleward-moving events moving into the polar cap, seen by the EISCAT Svalbard Radar (ESR). A pass of the DMSP-F15 satellite reveals that the open field lines near noon have been opened for some time: the more recently opened field lines were found closer to dusk where the flow transient and the poleward-moving event intersected the satellite pass. The events at Cluster have ion and electron characteristics predicted and observed by Lockwood and Hapgood (1998) for a Flux Transfer Event (FTE), with allowance for magnetospheric ion reflection at Alfvénic disturbances in the magnetopause reconnection layer. Like FTEs, the events are about 1 R E in their direction of motion and show a rise in the magnetic field strength, but unlike FTEs, in general, they show no pressure excess in their core and hence, no characteristic bipolar signature in the boundary-normal component. However, most of the events were observed when the magnetic field was southward, i.e. on the edge of the interior magnetic cusp, or when the field was parallel to the magnetic equatorial plane. Only when the satellite begins to emerge from the exterior boundary (when the field was northward), do the events start to show a pressure excess in their core and the consequent bipolar signature. We identify the events as the first observations of FTEs at middle altitudes.
Coordinated Cluster and ground-based instrument observations of transient changes in the magnetopause boundary layer during an interval of predominantly northward IMF: relation to reconnection pulses and FTE signatures
Auteurs :
D. Alcaydé, O. Amm, A. Balogh, R. Behlke, P.L. Blelly, J.M. Bosqued, C. Cully, W.F. Denig, E.F. Donovan, M.W. Dunlop, P. Eglitis, M.J. Engebretson, A.N. Fazakerley, H. Frey, R. Greenwald, T.L. Hansen, M.A. Hapgood, K. Kauristie, M. Lester, M. Lockwood, G. Lu, M.F. Marcucci, I.W. Mccrea, J. Moen, S.K. Morley, H.J. Opgenoorth, F. Pitout, P. Prikryl, G. Provan, T.I. Pulkkinen, Henri Rème, R. Stamper, A. Strømme, M.G.G.T. Taylor, A.P. Van Eyken, J. Waterman, M.N. Wild et J.A. Wild
Masquer le résumé
We study a series of transient entries into the low-latitude boundary layer (LLBL) of all four Cluster spacecraft during an outbound pass through the mid-afternoon magnetopause ( [ XGSM, YGSM, ZGSM ] ˜ [ 2, 7, 9 ] R E ). The events take place during an interval of northward IMF, as seen in the data from the ACE satellite and lagged by a propagation delay of 75 min that is welldefined by two separate studies: (1) the magnetospheric variations prior to the northward turning (Lockwood et al., 2001, this issue) and (2) the field clock angle seen by Cluster after it had emerged into the magnetosheath (Opgenoorth et al., 2001, this issue). With an additional lag of 16.5 min, the transient LLBL events correlate well with swings of the IMF clock angle (in GSM) to near 90°. Most of this additional lag is explained by ground-based observations, which reveal signatures of transient reconnection in the pre-noon sector that then take 10–15 min to propagate eastward to 15 MLT, where they are observed by Cluster. The eastward phase speed of these signatures agrees very well with the motion deduced by the cross-correlation of the signatures seen on the four Cluster spacecraft. The evidence that these events are reconnection pulses includes: transient erosion of the noon 630 nm (cusp/cleft) aurora to lower latitudes; transient and travelling enhancements of the flow into the polar cap, imaged by the AMIE technique; and poleward-moving events moving into the polar cap, seen by the EISCAT Svalbard Radar (ESR). A pass of the DMSP-F15 satellite reveals that the open field lines near noon have been opened for some time: the more recently opened field lines were found closer to dusk where the flow transient and the poleward-moving event intersected the satellite pass. The events at Cluster have ion and electron characteristics predicted and observed by Lockwood and Hapgood (1998) for a Flux Transfer Event (FTE), with allowance for magnetospheric ion reflection at Alfvénic disturbances in the magnetopause reconnection layer. Like FTEs, the events are about 1 R E in their direction of motion and show a rise in the magnetic field strength, but unlike FTEs, in general, they show no pressure excess in their core and hence, no characteristic bipolar signature in the boundary-normal component. However, most of the events were observed when the magnetic field was southward, i.e. on the edge of the interior magnetic cusp, or when the field was parallel to the magnetic equatorial plane. Only when the satellite begins to emerge from the exterior boundary (when the field was northward), do the events start to show a pressure excess in their core and the consequent bipolar signature. We identify the events as the first observations of FTEs at middle altitudes.
EISCAT/CRRES observations: nightside ionospheric ion outflow and oxygen-rich substorm injections
Auteurs :
A.D. Aylward, R.J. Bunting, S. Coles, N.G.J. Gazey, M. Grande, M. Lockwood, H. Opgenoorth, C.H. Perry, P.N. Smith et B. Wilken
Masquer le résumé
We present combined observations made near midnight by the EISCAT radar, all-sky cameras and the combined released and radiation efects satellite (CRRES) shortly before and during a substorm. In particular, we study a discrete, equatorward-drifting auroral arc, seen several degrees poleward of the onset region. The arc passes through the field-aligned beam of the EISCAT radar and is seen to be associated with a considerable upflow of ionospheric plasma. During the substorm, the CRRES satellite observed two major injections, 17 min apart, the second of which was dominated by O + ions. We show that the observed arc was in a suitable location in both latitude and MLT to have fed O + ions into the second injection and that the upward flux of ions associated with it was sufficient to explain the observed injection. We interpret these data as showing that arcs in the nightside plasma-sheet boundary layer could be the source of O + ions energised by a dipolarisation of the mid- and near-Earth tail, as opposed to ions ejected from the dayside ionosphere in the cleft ion fountain.
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