| 1. |
- Agapitov, Oleksiy, et al.
(författare)
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Multispacecraft observations of chorus emissions as a tool for the plasma density fluctuations' remote sensing
- 2011
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 116, s. A09222-
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Tidskriftsartikel (refereegranskat)abstract
- Discrete ELF/VLF chorus emissions are the most intense electromagnetic plasma waves that are observed in the radiation belts and in the outer magnetosphere of the Earth. They are assumed to propagate approximately along the magnetic field lines and are generated in source regions in the vicinity of the magnetic equator and in minimum B pockets in the dayside outer zone of the magnetosphere. The presence of plasma density irregularities along the raypath causes a loss of phase coherence of the chorus wave packets. These irregularities are often present around the plasmapause and in the radiation belts; they occur at scales ranging from a few meters up to several hundred kilometers and can be highly anisotropic. Such irregularities result in fluctuations of the dielectric permittivity, whose statistical properties can be studied making use of intersatellite correlations of whistler waves' phases and amplitudes. We demonstrate how the whistler-mode wave properties can be used to infer statistical characteristics of the density fluctuations. The analogy between weakly coupled oscillators under the action of uncorrelated random forces and wave propagation in a randomly fluctuating medium is used to determine the wave phase dependence on the duration of signal recording time. We study chorus whistler-mode waves observed by the Cluster WBD instrument and apply intersatellite correlation analysis to determine the statistical characteristics of the waveform phases and amplitudes. We then infer the statistical characteristics of the plasma density fluctuations and evaluate the spatial distribution of the irregularities using the same chorus events observed by the four Cluster spacecraft.
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| 2. |
- 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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| 3. |
- Fletcher, Leigh N., et al.
(författare)
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Jupiter Science Enabled by ESA's Jupiter Icy Moons Explorer
- 2023
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Ingår i: Space Science Reviews. - : Springer Nature. - 0038-6308 .- 1572-9672. ; 219:7
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Forskningsöversikt (refereegranskat)abstract
- ESA's Jupiter Icy Moons Explorer (JUICE) will provide a detailed investigation of the Jovian system in the 2030s, combining a suite of state-of-the-art instruments with an orbital tour tailored to maximise observing opportunities. We review the Jupiter science enabled by the JUICE mission, building on the legacy of discoveries from the Galileo, Cassini, and Juno missions, alongside ground- and space-based observatories. We focus on remote sensing of the climate, meteorology, and chemistry of the atmosphere and auroras from the cloud-forming weather layer, through the upper troposphere, into the stratosphere and ionosphere. The Jupiter orbital tour provides a wealth of opportunities for atmospheric and auroral science: global perspectives with its near-equatorial and inclined phases, sampling all phase angles from dayside to nightside, and investigating phenomena evolving on timescales from minutes to months. The remote sensing payload spans far-UV spectroscopy (50-210 nm), visible imaging (340-1080 nm), visible/near-infrared spectroscopy (0.49-5.56 & mu;m), and sub-millimetre sounding (near 530-625 GHz and 1067-1275 GHz). This is coupled to radio, stellar, and solar occultation opportunities to explore the atmosphere at high vertical resolution; and radio and plasma wave measurements of electric discharges in the Jovian atmosphere and auroras. Cross-disciplinary scientific investigations enable JUICE to explore coupling processes in giant planet atmospheres, to show how the atmosphere is connected to (i) the deep circulation and composition of the hydrogen-dominated interior; and (ii) to the currents and charged particle environments of the external magnetosphere. JUICE will provide a comprehensive characterisation of the atmosphere and auroras of this archetypal giant planet.
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| 4. |
- Jones, Geraint H., et al.
(författare)
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The Comet Interceptor Mission
- 2024
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Ingår i: Space Science Reviews. - : Springer Nature. - 0038-6308 .- 1572-9672. ; 220:1
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Tidskriftsartikel (refereegranskat)abstract
- Here we describe the novel, multi-point Comet Interceptor mission. It is dedicated to the exploration of a little-processed long-period comet, possibly entering the inner Solar System for the first time, or to encounter an interstellar object originating at another star. The objectives of the mission are to address the following questions: What are the surface composition, shape, morphology, and structure of the target object? What is the composition of the gas and dust in the coma, its connection to the nucleus, and the nature of its interaction with the solar wind? The mission was proposed to the European Space Agency in 2018, and formally adopted by the agency in June 2022, for launch in 2029 together with the Ariel mission. Comet Interceptor will take advantage of the opportunity presented by ESA’s F-Class call for fast, flexible, low-cost missions to which it was proposed. The call required a launch to a halo orbit around the Sun-Earth L2 point. The mission can take advantage of this placement to wait for the discovery of a suitable comet reachable with its minimum Δ V capability of 600 ms − 1 . Comet Interceptor will be unique in encountering and studying, at a nominal closest approach distance of 1000 km, a comet that represents a near-pristine sample of material from the formation of the Solar System. It will also add a capability that no previous cometary mission has had, which is to deploy two sub-probes – B1, provided by the Japanese space agency, JAXA, and B2 – that will follow different trajectories through the coma. While the main probe passes at a nominal 1000 km distance, probes B1 and B2 will follow different chords through the coma at distances of 850 km and 400 km, respectively. The result will be unique, simultaneous, spatially resolved information of the 3-dimensional properties of the target comet and its interaction with the space environment. We present the mission’s science background leading to these objectives, as well as an overview of the scientific instruments, mission design, and schedule.
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| 5. |
- Taubenschuss, Ulrich, et al.
(författare)
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Different types of whistler mode chorus in the equatorial source region
- 2015
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 42:20, s. 8271-8279
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Tidskriftsartikel (refereegranskat)abstract
- The Time History of Events and Macroscale Interactions during Substorms-D spacecraft crossed an active equatorial source region of whistler mode chorus rising tones on 23 October 2008. Rising tones are analyzed in terms of spectral and polarization characteristics, with special emphasis on wave normal angles. The latter exhibit large variations from quasi-parallel to oblique, even within single bursts, but seem to follow a definite pattern, which enables an unambiguous classification into five different groups. Furthermore, we discuss the frequently observed splitting of chorus bursts into a lower and an upper band around one half of the local electron cyclotron frequency. At chorus frequencies close to the gap, we find significantly lowered wave planarities and a tendency of wave normal angles to approach the Gendrin angle.
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| 6. |
- Taubenschuss, Ulrich, et al.
(författare)
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Wave normal angles of whistler mode chorus rising and falling tones
- 2014
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Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 119:12
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Tidskriftsartikel (refereegranskat)abstract
- We present a study of wave normal angles (theta(k)) of whistler mode chorus emission as observed by Time History of Events and Macroscale Interactions during Substorms (THEMIS) during the year 2008. The three inner THEMIS satellites THA, THD, and THE usually orbit Earth close to the dipole magnetic equator (+/- 20 degrees), covering a large range of L shells from the plasmasphere out to the magnetopause. Waveform measurements of electric and magnetic fields enable a detailed polarization analysis of chorus below 4 kHz. When displayed in a frequency-theta(k) histogram, four characteristic regions of occurrence are evident. They are separated by gaps at f/f(c,e) approximate to 0.5 (f is the chorus frequency, f(c,e) is the local electron cyclotron frequency) and at theta(k) similar to 40 degrees. Below theta(k) similar to 40 degrees, the average value for theta(k) is predominantly field aligned, but slightly increasing with frequency toward half of f(c,e) (theta(k) up to 20 degrees). Above half of f(c,e), the average theta(k) is again decreasing with frequency. Above theta(k) similar to 40 degrees, wave normal angles are usually close to the resonance cone angle. Furthermore, we present a detailed comparison of electric and magnetic fields of chorus rising and falling tones. Falling tones exhibit peaks in occurrence solely for theta(k) > 40 degrees and are propagating close to the resonance cone angle. Nevertheless, when comparing rising tones to falling tones at theta(k) > 40 degrees, the ratio of magnetic to electric field shows no significant differences. Thus, we conclude that falling tones are generated under similar conditions as rising tones, with common source regions close to the magnetic equatorial plane.
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