| 1. |
- Arridge, Christopher S., et al.
(författare)
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Uranus Pathfinder : exploring the origins and evolution of Ice Giant planets
- 2012
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Ingår i: Experimental astronomy. - : Springer Science and Business Media LLC. - 0922-6435 .- 1572-9508. ; 33:2-3, s. 753-791
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Tidskriftsartikel (refereegranskat)abstract
- The "Ice Giants" Uranus and Neptune are a different class of planet compared to Jupiter and Saturn. Studying these objects is important for furthering our understanding of the formation and evolution of the planets, and unravelling the fundamental physical and chemical processes in the Solar System. The importance of filling these gaps in our knowledge of the Solar System is particularly acute when trying to apply our understanding to the numerous planetary systems that have been discovered around other stars. The Uranus Pathfinder (UP) mission thus represents the quintessential aspects of the objectives of the European planetary community as expressed in ESA's Cosmic Vision 2015-2025. UP was proposed to the European Space Agency's M3 call for medium-class missions in 2010 and proposed to be the first orbiter of an Ice Giant planet. As the most accessible Ice Giant within the M-class mission envelope Uranus was identified as the mission target. Although not selected for this call the UP mission concept provides a baseline framework for the exploration of Uranus with existing low-cost platforms and underlines the need to develop power sources suitable for the outer Solar System. The UP science case is based around exploring the origins, evolution, and processes at work in Ice Giant planetary systems. Three broad themes were identified: (1) Uranus as an Ice Giant, (2) An Ice Giant planetary system, and (3) An asymmetric magnetosphere. Due to the long interplanetary transfer from Earth to Uranus a significant cruise-phase science theme was also developed. The UP mission concept calls for the use of a Mars Express/Rosetta-type platform to launch on a Soyuz-Fregat in 2021 and entering into an eccentric polar orbit around Uranus in the 2036-2037 timeframe. The science payload has a strong heritage in Europe and beyond and requires no significant technology developments.
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| 2. |
- Welling, Daniel T., et al.
(författare)
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The Earth : Plasma Sources, Losses, and Transport Processes
- 2015
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Ingår i: Space Science Reviews. - : Springer Science and Business Media LLC. - 0038-6308 .- 1572-9672. ; 192:1-4, s. 145-208
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Forskningsöversikt (refereegranskat)abstract
- This paper reviews the state of knowledge concerning the source of magnetospheric plasma at Earth. Source of plasma, its acceleration and transport throughout the system, its consequences on system dynamics, and its loss are all discussed. Both observational and modeling advances since the last time this subject was covered in detail (Hultqvist et al., Magnetospheric Plasma Sources and Losses, 1999) are addressed.
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| 3. |
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| 4. |
- Backrud-Ivgren, Marie, et al.
(författare)
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Cluster observations and theoretical identification of broadband waves in the auroral region
- 2005
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Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 23:12, 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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| 5. |
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| 6. |
- Backrud, Marie, et al.
(författare)
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Interferometric Identification of Ion Acoustic Broadband Waves in the Auroral Region : CLUSTER Observations
- 2005
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 32:21
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Tidskriftsartikel (refereegranskat)abstract
- [1] We determine the phase velocity and k vector for parallel and oblique broadband extremely low frequency, ELF, waves on nightside auroral magnetic field lines at altitudes around 4.6 RE. We use internal burst mode data from the EFW electric field and wave instrument onboard the Cluster spacecraft to retrieve phase differences between the four probes of the instrument. The retrieved characteristic phase velocity is of the order of the ion acoustic speed and larger than the thermal velocity of the protons. The typical wavelength obtained from interferometry is around the proton gyro radius and always larger than the Debye length. We find that in regions with essentially no suprathermal electrons above a few tens of eV the observed broadband waves above the proton gyro frequency are consistent with upgoing ion acoustic and oblique ion acoustic waves.
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| 7. |
- Chen, Li-Jen, et al.
(författare)
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Multispacecraft observations of the electron current sheet, neighboring magnetic islands, and electron acceleration during magnetotail reconnection
- 2009
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 16:5, s. 056501-
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Tidskriftsartikel (refereegranskat)abstract
- Open questions concerning structures and dynamics of diffusion regions and electron acceleration in collisionless magnetic reconnection are addressed based on data from the four-spacecraft mission Cluster and particle-in-cell simulations. Using time series of electron distribution functions measured by the four spacecraft, distinct electron regions around a reconnection layer are mapped out to set the framework for studying diffusion regions. A spatially extended electron current sheet (ecs), a series of magnetic islands, and bursts of energetic electrons within islands are identified during magnetotail reconnection with no appreciable guide field. The ecs is collocated with a layer of electron-scale electric fields normal to the ecs and pointing toward the ecs center plane. Both the observed electron and ion densities vary by more than a factor of 2 within one ion skin depth north and south of the ecs, and from the ecs into magnetic islands. Within each of the identified islands, there is a burst of suprathermal electrons whose fluxes peak at density compression sites [L.-J. Chen , Nat. Phys. 4, 19 (2008)] and whose energy spectra exhibit power laws with indices ranging from 6 to 7.3. These results indicate that the in-plane electric field normal to the ecs can be of the electron scale at certain phases of reconnection, electrons and ions are highly compressible within the ion diffusion region, and for reconnection involving magnetic islands, primary electron acceleration occurs within the islands.
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| 8. |
- Johansson, Tommy, et al.
(författare)
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Intense high-altitude auroral electric fields : temporal and spatial characteristics
- 2004
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Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 22:7, s. 2485-2495
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Tidskriftsartikel (refereegranskat)abstract
- Cluster electric field, magnetic field, and energetic electron data are analyzed for two events of intense auroral electric field variations, both encountered in the Plasma Sheet Boundary Layer (PSBL), in the evening local time sector, and at approximately 5 R-E geocentric distance. The most intense electric fields (peaking at 450 and 1600 mV/m, respectively) were found to be quasi-static, unipolar, relatively stable on the time scale of at least half a minute, and associated with moving downward FAC sheets (peaking at similar to10 muA/m(2)), downward Poynting flux (peaking at similar to35 mW/m(2)), and upward electron beams with characteristic energies consistent with the perpendicular potentials (all values being mapped to 1 R-E geocentric distance). For these two events in the return current region, quasi-static electric field structures and associated FACs were found to dominate the upward acceleration of electrons, as well as the energy transport between the ionosphere and the magnetosphere, although Alfven waves clearly also contributed to these processes.
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| 9. |
- Johansson, Tommy, et al.
(författare)
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On the profile of intense high-altitude auroral electric fields at magnetospheric boundaries
- 2006
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Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 24:6, s. 1713-1723
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Tidskriftsartikel (refereegranskat)abstract
- The profile of intense high-altitude electric fields on auroral field lines has been studied using Cluster data. A total of 41 events with mapped electric field magnitudes in the range between 0.5-1 V/m were examined, 27 of which were co-located with a plasma boundary, defined by gradients in particle flux, plasma density and plasma temperature. Monopolar electric field profiles were observed in 11 and bipolar electric field profiles in 16 of these boundary-associated electric field events. Of the monopolar fields, all but one occurred at the polar cap boundary in the late evening and midnight sectors, and the electric fields were typically directed equatorward, whereas the bipolar fields all occurred at plasma boundaries clearly within the plasma sheet. These results support the prediction by Marklund et al. (2004), that the electric field profile depends on whether plasma populations, able to support intense field-aligned currents and closure by Pedersen currents, exist on both sides, or one side only, of the boundary.
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| 10. |
- Li, Bin, et al.
(författare)
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Inverted-V and low-energy broadband electron acceleration features of multiple auroras within a large-scale surge
- 2013
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Ingår i: Journal of Geophysical Research: Space Physics. - : American Geophysical Union (AGU). - 2169-9380. ; 118:9, s. 5543-5552
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Tidskriftsartikel (refereegranskat)abstract
- Results are presented from a Cluster C2 satellite crossing through the acceleration region of multiple auroral structures within a large-scale surge, simultaneously monitored by DMSP F17 imager data. The magnetic and electric field data are consistent with the auroral distribution at large and medium scales. We identify the quasi-static acceleration above and below C2 orbit by downgoing inverted-V electrons and parallel electric potential drops, respectively. In the poleward surge region, within or adjacent to the inverted-V arcs, intense low-energy (broadband) electron fluxes are seen as well as a rough equality between E/B and the Alfven velocity, suggesting that these are of Alfvenic origin. The most poleward and equatorward auroral structure is found to be Alfvenic and quasi-static, respectively. In between, the structures are of mixed origin. We estimate the relative role of the acceleration processes by the contributions to the downward electron energy flux by electrons above and below 1.62keV. Although these are local estimates, they should be representative also below Cluster altitude, except for two regions of intense downward Poynting flux, the power of which will be dissipated at lower altitudes and increasing the Alfvenic contribution. This is also supported by intense fluxes of low-energy, broadband, upgoing electrons observed within these regions. Otherwise, the inverted-V contribution dominates for most of the auroral structures observed by Cluster. The Alfvenic contribution to the mixed arc emissions is to extend these to higher altitudes, as shown by numerical simulation results.
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