| 1. |
- Wahlund, J. E., et al.
(författare)
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Detection of dusty plasma near the E-ring of Saturn
- 2009
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Ingår i: Planetary and Space Science. - : Elsevier BV. - 0032-0633 .- 1873-5088. ; 57:14-15, s. 1795-1806
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Tidskriftsartikel (refereegranskat)abstract
- We present several independent in-situ measurements, which provide evidence that charged dust in the E-ring interacts collectively with the dense surrounding plasma disk of Saturn, i.e., form a system of dust-plasma interaction. The results are based on data sampled by the Radio and Plasma Wave Science (RPWS) investigation onboard Cassini, which allows for interferometry of plasma density inhomogeneities (delta n/n) with two antenna elements and a Langmuir probe sensor. The interferometer experiment detects two ion populations: one co-rotating with the planetary magnetic field and another moving with near Keplerian speed around Saturn. The full range of RPWS measurements indicates that the Keplerian population consists of colder ions (T-i
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| 2. |
- Backrud, M., et al.
(författare)
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Cluster observations and theoretical explanations of broadband waves in the auroral region
- 2005
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Ingår i: Annales Geophysicae. - : Copernicus Publications. - 1432-0576. ; 23, s. 3739-3752
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Tidskriftsartikel (refereegranskat)abstract
- Broadband waves are common on auroral field lines. We use two different methods to study the polarization of the waves at 10 to 180 Hz observed by the Cluster spacecraft at altitudes of about 4 Earth radii in the nightside auroral region. Observations of electric and magnetic wave fields, together with electron and ion data, are used as input to the methods. We find that much of the wave emissions are consistent with linear waves in homogeneous plasma. Observed waves with a large electric field perpendicular to the geomagnetic field are more common (electrostatic ion cyclotron waves), while ion acoustic waves with a large parallel electric field appear in smaller regions without suprathermal (tens of eV) plasma. The regions void of suprathermal plasma are interpreted as parallel potential drops of a few hundred volts.
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| 3. |
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| 4. |
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| 5. |
- Morooka, Michiko, et al.
(författare)
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The electron density of Saturn's magnetosphere
- 2009
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Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 27:7, s. 2971-2991
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated statistically the electron density below 5 cm(-3) in the magnetosphere of Saturn (7-80 R-S, Saturn radii) using 44 orbits of the floating potential data from the RPWS Langmuir probe (LP) onboard Cassini. The density distribution shows a clear dependence on the distance from the Saturnian rotation axis (root X-2 + Y-2) as well as on the distance from the equatorial plane (vertical bar Z vertical bar), indicating a disc-like structure. From the characteristics of the density distribution, we have identified three regions: the extension of the plasma disc, the magnetodisc region, and the lobe regions. The plasma disc region is at L<15, where L is the radial distance to the equatorial crossing of the dipole magnetic field line, and confined to vertical bar Z vertical bar <5 R-S. The magnetodisc is located beyond L=15, and its density has a large variability. The variability has quasi-periodic characteristics with a periodicity corresponding to the planetary rotation. For Z > 15 R-S, the magnetospheric density distribution becomes constant in Z. However, the density still varies quasi-periodically with the planetary rotation also in this region. In fact, the quasi-periodic variation has been observed all over the magnetosphere beyond L=15. The region above Z=15 R-S is identified as the lobe region. We also found that the magnetosphere can occasionally move latitudinally under the control of the density in the magnetosphere and the solar wind. From the empirical distributions of the electron densities obtained in this study, we have constructed an electron density model of the Saturnian nightside magnetosphere beyond 7 R-S. The obtained model can well reproduce the observed density distribution, and can thus be useful for magnetospheric modelling studies.
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| 6. |
- Wahlund, J E, et al.
(författare)
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Science opportunities with a double Langmuir probe and electric field experiment for JIMO
- 2005
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Ingår i: PLANETARY ATMOSPHERES, IONOSPHERES, AND MAGNETOSPHERES. - : Elsevier BV. ; , s. 2110-2119
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Konferensbidrag (refereegranskat)abstract
- The three icy Galilean moons of Jupiter: Callisto, Ganymede, and Europa, offer a range of exciting science opportunities for space physics and aeronomy. They all have thin atmospheres with residence times of a few days at most. The surface interactions with the space environment determine the atmospheric and ionospheric properties. The Jupiter Icy Moons Orbiter (JIMO) gives possibilities to investigate the weathering properties of their surfaces and volatile material expelled from their interiors. The atmospheres and the ionized ionospheric components of the Galilean moons (including the volcanic moon Io) interact strongly with the co-rotating magnetosphere of Jupiter. This interaction is dynamic and for example triggers energy transfer processes that give rise to auroral signatures at Jupiter. The icy moon's ionospheres are likewise highly variable in time and estimated peak electron densities vary between 1000 and 20,000 cm(-3) near their surfaces. A particularly interesting interaction occurs between the magnetosphere of Jupiter and the mini-magnetosphere of Ganymede and its ionosphere. A double-Langmuir probe (LP) experiment orbiting the moons at a short distance for several months will give valuable insight into these processes. Foremost the LP measures in situ plasma density and temperatures of the ionospheric components of the moons with high time resolution and thereby provides estimates of key parameters for the dynamical behaviour of surface weathering and magnetospheric influences. In addition many other physical parameters important to the dynamics of these systems can be estimated with such an instrument, like the plasma flow and the DC electric field. Recent results from the LP part of the Radio and Plasma Wave Science (RPWS) on board the Cassini/Huygens spacecraft orbiting Saturn show that an LP works in extended plasma parameter domains with very good science return.
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| 7. |
- Stenberg, Gabriella, et al.
(författare)
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Electron-scale sheets of whistlers close to the magnetopause
- 2005
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Ingår i: Annales Geophysicae. - Göttingen : Copernicus gesellschaft. - 0992-7689 .- 1432-0576. ; 23:12, s. 3715-3725
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Tidskriftsartikel (refereegranskat)abstract
- Whistler emissions close to the magnetopause on the magnetospheric side are investigated using the four Cluster spacecraft. The waves are found to be generated in thin (electron-scale) sheets moving with the plasma drift velocity. A feature in the electron data coincides with the waves; hot magnetospheric electrons disappear for a few satellite spins. This produces or enhances a temperature anisotropy, which is found to be responsible for the generation of the whistler mode waves. The high energy electrons are thought to be lost through the magnetopause and we suggest that the field lines, on which the waves are generated, are directly connected to a reconnection diffusion region at the magnetopause.
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