| 1. |
- Escoubet, C. P., et al.
(författare)
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Imaging the magnetosphere using ISEE-1 spacecraft potential
- 1996
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Ingår i: European Space Agency, (Special Publication) ESA SP. - 0379-6566. ; :392, s. 179-187
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Tidskriftsartikel (refereegranskat)abstract
- The potential of ISEE 1 spacecraft has been used to derived the plasma density in the magnetosphere and its environment. First we show that using the equilibrium of currents flowing in and out of a spacecraft, we could derive numerically a relation between the spacecraft potential and the density of the surrounding plasma. After verifying that this relation was in good agreement with the measurement of the density made by other instruments during selected periods of time, we apply this relation to the spacecraft potential measured continuously from 1977 to 1984 on ISEE-1. An image of the plasma density in the magnetosphere and its environment is obtained as a result. All principal magnetospheric regions are clearly identified, from the solar wind with a density around 5 cm-3 , the magnetosheath around 50 cm-3, the magnetosphere around 1 cm-3, the plasma sheet around 0.5 cm-3 and finally the more tenuous tail lobes below 0.1 cm-3. The plasma density was observed slightly higher on the dawnside than on the dusk side of the magnetosphere. In addition the magnetosheath was closer to the Earth on the dawnside than on the duskside. When the magnetic activity increased (recorded by the AE index), the dayside magnetosphere was compressed/eroded by about 1 to 2 RE while the plasmasphere/inner magnetosphere became quite irregular and expanded in the dawn-midnight and in the dusk-noon sectors. In addition, during high magnetic activity, the plasmasheet at Ygsm = 0 was thicker and denser than at low activity. On the other hand the flanks of the plasmasheet were thinner and less dense during high activity than during low activity.
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| 2. |
- Feldstein, Yakov I., et al.
(författare)
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To directly driven and loading-unloading processes during substorm
- 1996
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Ingår i: European Space Agency, (Special Publication) ESA SP. - 0379-6566. ; :389, s. 69-74
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Tidskriftsartikel (refereegranskat)abstract
- Model calculations of the electric fields in the high-latitude ionosphere are compared to measurements made by the Viking satellite during August 3, 1986 pass. The model calculations are based on the IZMEM procedure, where the electric field and currents in the ionosphere are given as functions of the interplanetary magnetic field (IMF). The event chosen correspond to the growth phase of substorm. The correlation between the model results and the satellite data is high, which assumes directly driven of the magnetosphere by the solar wind. Similar high correlation exists between the electric field in the solar wind (V*Bs) and AL magnetic activity indices, if time delays between the V*Bs observations in space and magnetic activity above the Earth's ground are taken into account. It is concluded, that the directly driven response of the magnetosphere to highly variable solar wind electric field is the main feature of geomagnetic activity at high latitudes.
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| 3. |
- Marklund, Göran, et al.
(författare)
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Astrid 2, A low-budget microsatellite mission for auroral research
- 1997
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Ingår i: European Space Agency, (Special Publication) ESA SP. - 0379-6566. ; :397, s. 387-394
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Tidskriftsartikel (refereegranskat)abstract
- The next in the Astrid series of low-budget microsatellite missions will be devoted to classical auroral research. The challenge of this mission is to demonstrate the possibility to carry out comprehensive auroral investigations on a microsatellite platform having the size 0.45 × 0.45 × 0.3 m at a cost of about 2 MUSD. A successful mission will open up new less expensive ways carrying out auroral research in the future, ways which are complementary to the more ambitious programmes run within ESA and NASA. Of particular interest are multipoint measurements within the auroral acceleration region using clusters of microsatellites. New light-weight and compact instruments and deployment systems have been developed for the Astrid-2 mission. The payload will carry an integrated electric and magnetic field instrument, including a Langmuir probe, a lightweight ion and electron spectrometer, and two spin-scanning UV photometers for Lyman α and oxygen emissions in the aurora. The electric field probes will be deployed using a newly developed light-weight system for wire boom deployment. Other novel features to be used on Astrid-2 are data compression and data filtering. Astrid-2 is to be launched on a Kosmos vehicle from Plesetsk in 1997 into an 83° inclination circular orbit at 1000 km altitude. The mission will use a geographically distributed ground station network for high-speed S-band data reception, one station to be located at Solna, Sweden and another at the South African Antarctic base SANAE.
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| 4. |
- Popielawska, B., et al.
(författare)
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An imprint of the quiet plasma sheet structure at the orbit of viking : Magnetosphere without substorms
- 1996
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Ingår i: European Space Agency, (Special Publication) ESA SP. - 0379-6566. ; :389, s. 133-139
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Tidskriftsartikel (refereegranskat)abstract
- We present a study of the plasma sheet structure as seen on VIKING during prolonged periods of magnetic quiescence. The ion and electron spectrograms, the electric field data and field-aligned current signatures in the magnetic field data are examined. A special attention is paid to cases when the Low Latitude Boundary Layer-like plasma is seen deep in the nightside at latitudes which apparently map to close geocentric distances as it implies an exotic plasma circulation in the tail. An attempt has been made to infer from VIKING data how the quiet plasma sheet is formed, whether it originates mainly from the mantle source via the interaction with the distant tail current sheet or whether the lateral transport of the Low Latitude Boundary Layer (LLBL) from the tail flanks (with essentially adiabatic particle motion) takes place followed by the sunward convection in the central part of the near-Earth tail. The VIKING plasma and electric field data suggest that the last mechanism is decisive for plasma sheet structuring during prolonged periods of northward IMF.
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| 5. |
- Rothwell, P.L., et al.
(författare)
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Inertial currents and substorm onsets
- 1996
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Ingår i: European Space Agency, (Special Publication) ESA SP-389. - 0379-6566. ; , s. 447-452
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Tidskriftsartikel (refereegranskat)abstract
- When magnetic field lines are sufficiently stretched during the substorm growth phase, in the equatorial plane the earthward ExB ion drift velocity can become comparable to the ion gyration velocity. Under these conditions inertial currents can become quite important. Using a two-dimensional model we find that O+ ions injected from the ionosphere into the equatorial plane at high latitudes will drift eastward at radial distances less than -10 RE because the inertial drift dominates and westward at distances closer to the earth because the magnetic gradient drift dominates. The inertial eastward drift gives rise to a current which in terms of JxB is consistent with the convective deceleration of the earthward drift velocity due to higher values of B. Similarly, momentum balance requires that the convective acceleration of the westward drift velocity should be consistent with a tailward inertial current. Therefore, an equatorial current wedge system with eastward and tailward current components naturally arises from the ion dynamics. In a future paper a three-dimensional treatment will determine whether curvature drift masks the eastward inertial drift of the oxygen ions.
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