| 1. |
- Edberg, Niklas J. T., et al.
(författare)
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Solar wind interaction with comet 67P : Impacts of corotating interaction regions
- 2016
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Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 121:2, s. 949-965
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Tidskriftsartikel (refereegranskat)abstract
- We present observations from the Rosetta Plasma Consortium of the effects of stormy solar wind on comet 67P/Churyumov-Gerasimenko. Four corotating interaction regions (CIRs), where the first event has possibly merged with a coronal mass ejection, are traced from Earth via Mars (using Mars Express and Mars Atmosphere and Volatile EvolutioN mission) to comet 67P from October to December 2014. When the comet is 3.1-2.7AU from the Sun and the neutral outgassing rate approximate to 10(25)-10(26)s(-1), the CIRs significantly influence the cometary plasma environment at altitudes down to 10-30km. The ionospheric low-energy (approximate to 5eV) plasma density increases significantly in all events, by a factor of >2 in events 1 and 2 but less in events 3 and 4. The spacecraft potential drops below -20V upon impact when the flux of electrons increases. The increased density is likely caused by compression of the plasma environment, increased particle impact ionization, and possibly charge exchange processes and acceleration of mass-loaded plasma back to the comet ionosphere. During all events, the fluxes of suprathermal (approximate to 10-100eV) electrons increase significantly, suggesting that the heating mechanism of these electrons is coupled to the solar wind energy input. At impact the magnetic field strength in the coma increases by a factor of 2-5 as more interplanetary magnetic field piles up around the comet. During two CIR impact events, we observe possible plasma boundaries forming, or moving past Rosetta, as the strong solar wind compresses the cometary plasma environment. We also discuss the possibility of seeing some signatures of the ionospheric response to tail disconnection events.
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| 2. |
- Poppe, A.R., et al.
(författare)
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ARTEMIS observations of extreme diamagnetic fields in the lunar wake
- 2014
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 41:11, s. 3766-3773
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Tidskriftsartikel (refereegranskat)abstract
- We present two Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun ( ARTEMIS) observations of diamagnetic fields in the lunar wake at strengths exceeding twice the ambient magnetic field during high plasma beta conditions. The first observation was 350 km from the lunar surface while the Moon was located in the terrestrial magnetosheath with elevated particle temperatures. The second observation was in the solar wind ranging from 500 to 2000 km downstream, with a relatively low magnetic field strength of approximately 1.6 nT. In both cases, the plasma beta exceeded 10. We discuss the observations and compare the data to hybrid plasma simulations in order to validate the model under such extreme conditions and to elucidate the global structure of the lunar wake during these observations. The extreme nature of the diamagnetic field in the lunar wake provides an important end-member test case for theoretical and modeling studies of the various plasma processes operating in the lunar wake.
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| 3. |
- Tao, J. B., et al.
(författare)
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Kinetic instabilities in the lunar wake : ARTEMIS observations
- 2012
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 117, s. A03106-
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Tidskriftsartikel (refereegranskat)abstract
- The Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) mission is a new two-probe lunar mission derived from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission. On 13 February 2010, one of the two probes, ARTEMIS P1 (formerly THEMIS-B), made the first lunar wake flyby of the mission. We present detailed analysis of the electrostatic waves observed on the outbound side of the flyby that were associated with electron beams. Halekas et al. (2011) derived a net potential across the lunar wake from observations and suggested that the net potential generated the observed electron beams and the electron beams in turn excited the observed electrostatic waves due to kinetic instabilities. The wavelengths and velocities of the electrostatic waves are estimated, using high-resolution electric field instrument data with cross-spectrum analysis and cross-correlation analysis. In general, the estimated wavelengths vary from a few hundred meters to a couple of thousand meters. The estimated phase velocities are on the order of 1000 km s(-1). In addition, we perform 1-D Vlasov simulations to help identify the mode of the observed electrostatic waves. We conclude that the observed electrostatic waves are likely on the electron beam mode branch.
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| 4. |
- Zhou, X.-Z., et al.
(författare)
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Lunar dayside current in the terrestrial lobe: ARTEMIS observations
- 2014
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Ingår i: Journal of Geophysical Research - Space Physics. - : John Wiley & Sons. - 2169-9380 .- 2169-9402. ; 119:5, s. 3381-3391
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Tidskriftsartikel (refereegranskat)abstract
- We report Acceleration, Reconnection, Turbulence and Electrodynamics of Moon's Interaction with the Sun (ARTEMIS) dual-probe observations of two events in the terrestrial magnetotail lobe, both characterized by upward moving heavy ions of lunar origin at one of the probes that is magnetically connected with the dayside lunar surface. By treating magnetic measurements at the other probe as the unperturbed lobe fields, we obtain background-subtracted magnetic perturbations (most significantly in Bz) when the first probe moved in the dawn-dusk direction across flux tubes magnetically connected to the Moon. These magnetic perturbations indicate the presence of field-aligned current above the lunar surface. By examining possible carriers of field-aligned current, we find that lunar heavy ions and accompanying electrons both contribute considerably to the current. Observations of the field-aligned current also suggest that the charging process at the dayside lunar surface and the associated lobe plasma environment, which have traditionally been viewed as a one-dimensional current balance problem, are actually more complicated. These observations give the first insights into how heavy ions affect the lunar dayside environment in terms of multispecies plasma dynamics.
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