| 1. |
- Backrud-Ivgren, Marie, et al.
(author)
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Cluster observations and theoretical identification of broadband waves in the auroral region
- 2005
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In: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 23:12, s. 3739-3752
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Journal article (peer-reviewed)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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| 2. |
- Blomberg, Lars, et al.
(author)
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Electric Field Diagnostics in the Jovian System : Brief Scientific Case and Instrumentation Overview
- 2006
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In: Proceedings of the 6th IAA International Conference on Low-Cost Planetary Missions. ; , s. 335-340
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Conference paper (other academic/artistic)abstract
- The Jovian plasma environment exhibits a variety of plasma flow interactions with magnetised as well as unmagnetised bodies, making it a good venue for furthering our understanding of solar wind - magnetosphere / ionosphere interactions. On an overall scale the solar wind interacts with the Jovian magnetosphere, much like at Earth but with vastly different temporal and spatial scales. Inside the Jovian magnetosphere the co-rotating plasma interacts with the inner moons. The latter interaction is slower and more stable than the corresponding interaction between the solar wind and the planets, and can thus provide additional information on the principles of the interaction mechanisms. Because of the wealth of expected low-frequency waves, as well as the predicted quasi-static electric fields and plasma drifts in the interaction regions between different parts of the Jovian system, a most valuable component in future payloads would be a double-probe electric field instrument. Recent developments in low-mass instrumentation facilitate electric field measurements on spinning planetary spacecraft, which we here exemplify.
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| 3. |
- Morooka, Michiko, et al.
(author)
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The electron density of Saturn's magnetosphere
- 2009
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In: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 27:7, s. 2971-2991
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Journal article (peer-reviewed)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, Jan-Erik, et al.
(author)
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Cold Plasma Diagnostics in the Jovian System : Brief Scientific Case and Instrumentation Overview
- 2006
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In: Proceedings of the 6th IAA International Conference on Low-Cost Planetary Missions. ; , s. 341-346
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Conference paper (other academic/artistic)abstract
- The Jovian magnetosphere equatorial region is filled with cold dense plasma that in a broad sense co-rotate with its magnetic field. The volcanic moon Io, which expels sodium, sulphur and oxygen containing species, dominates as a source for this cold plasma. The three icy Galilean moons (Callisto, Ganymede, and Europa) also contribute with water group and oxygen ions. All the Galilean moons have thin atmospheres with residence times of a few days at most. Their ionized ionospheric components interact dynamically with the co-rotating magnetosphere of Jupiter and for example triggers energy transfer processes that give rise to auroral signatures at Jupiter. On these moons the surface interactions with the space environment determine their atmospheric and ionospheric properties. The range of processes associated with the Jovian magnetospheric interaction with the Galilean moons, where the cold dense plasma expelled from these moons play a key role, are not well understood. Conversely, the volatile material expelled from their interiors is important for our understanding of the Jovian magnetosphere dynamics and energy transfer. A Langmuir probe investigation, giving in-situ plasma density, temperatures, UV intensity and plasma speed with high time resolution, would be a most valuable component for future payloads to the Jupiter system. Recent developments in low-mass instrumentation facilitate Langmuir probe in situ measurements on such missions.
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| 7. |
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| 8. |
- Yaroshenko, V.V., et al.
(author)
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Characteristics of charged dust inferred from the Cassini RPWS measurements in the vicinity of Enceladus
- 2009
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In: Planetary and Space Science. - : Elsevier BV. - 0032-0633 .- 1873-5088. ; 57:14-15, s. 1807-1812
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Journal article (peer-reviewed)abstract
- The data obtained by the Cassini Radio and Plasma Wave Science (RPWS) instrument during the shallow (17.02.2005) and the steep (14.07.2005) crossings of the E-ring revealed a considerable electron depletion in proximity to Enceladus's orbit (the difference between the ion and electron densities can reach similar to 70 cm(-3)). Assuming that this depletion is a signature of the presence of charged dust particles, the main characteristics of dust down to submicron sized particles are derived. The differential size distribution is found to be well described by a power law with an index mu similar to 5.5-6 for the lower size limit a(min) = 0.03 mu m and mu similar to 7.3-8 for a(min) = 0.1 mu m. The calculated average integral dust number density is weakly affected by values of mu and a(min). For a greater than or similar to 0.1 mu m, both flybys gave the maximum dust density about 0.1-0.3 cm(-3) in the vicinity of Enceladus. Our results imply that the dust structure near Enceladus is characterized by approximately the same vertical length scale of 8000 km and reaches a maximum at the same radial distance (displaced outward of the orbit of Enceladus) as found by Kempf et al. [2008. The E-ring in the vicinity of Enceladus. Spatial distribution and properties of the ring particles. Icarus 193, 420-437], from the dust impact data.
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| 9. |
- Yordanova, Emiliya, et al.
(author)
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Energy input from the exterior cusp into the ionosphere : Correlated ground-based and satellite observations
- 2007
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In: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 34:4, s. L04102-
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Journal article (peer-reviewed)abstract
- The energy transport from the exterior cusp into the ionosphere is investigated using coordinated ground-based (EISCAT and MIRACLE) and satellite ( Cluster) observations. EISCAT and MIRACLE data are used to estimate the plasma heating in the F-region and the Joule heating in the E-region. Cluster measurements are used to derive the electromagnetic and particle energy fluxes at the high altitudes. These fluxes are then compared with the energy deposition into the ionospheric cusp during a 30 minutes long time interval in which Cluster and EISCAT are nearly conjugated. It is shown that the particles seen at about 9 Re in the exterior cusp carry an earthward energy flux that corresponds to the observed heating of the F-region. The estimated earthward Poynting flux is more than enough to account for the Joule heating in the E-region.
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