| 1. |
- Escoubet, C P, et al.
(författare)
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Density in the magnetosphere inferred from ISEE 1 spacecraft potential
- 1997
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Ingår i: JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS. - ROYAL INST TECHNOL,ALFVEN LAB,DIV PLASMA PHYS,S-10044 STOCKHOLM,SWEDEN.. ; 102:A8, s. 17595-17609
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Tidskriftsartikel (refereegranskat)abstract
- The potential of ISEE 1 spacecraft has been used to derive the plasma density in the magnetosphere and its environment. First, we show that using the equilibrium of currents flowing in and out of a spacecraft, we could numerically derive a relation between the spacecraft potential and the density of the surrounding plasma, After verifying: that this relation was in good agreement with the measurement of the density made by other instruments during selected periods of time, we apply this relation to the spacecraft potential measured continuously from 1977 to 1984 on ISEE 1, An image of the plasma density in the magnetosphere and its environment is obtained as a result, All principal magnetospheric regions are clearly identified: the solar wind with a density around 5 cm(-3) : the magnetosheath with a density around 50 cm(-3), the magnetosphere with a density around 1 cm(-3) the plasma sheet with a density around 0.5 cm(-3), and finally, the more tenuous tail lobes with a density below 0.1 cm(-3), The plasma density was observed slightly higher on the dawnside than on the duskside of the magnetosphere, In addition, the magnetosheath was closer to the Earth on the dawnside than on the duskside, When the magnetic activity increased (recorded by the AE index), the dayside magnetosphere was compressed/eroded by about 1 to 2 R-E, while the plasmasphere/inner magnetosphere became quite irregular and expanded in the dawn-midnight and in the dusk-noon sectors, In addition, during high magnetic activity, the plasma sheet at Y-GSM = 0 was thicker and slightly denser than at low-activity, On the other hand, the flanks of the plasma sheet were thinner and slightly less dense during high-activity than during low-activity.
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| 2. |
- Escoubet, C. P., et al.
(författare)
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Imaging the magnetosphere using ISEE-1 spacecraft potential
- 1996
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Ingår i: European Space Agency, (Special Publication) ESA SP. - 0379-6566. ; :392, s. 179-187
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Tidskriftsartikel (refereegranskat)abstract
- The potential of ISEE 1 spacecraft has been used to derived the plasma density in the magnetosphere and its environment. First we show that using the equilibrium of currents flowing in and out of a spacecraft, we could derive numerically a relation between the spacecraft potential and the density of the surrounding plasma. After verifying that this relation was in good agreement with the measurement of the density made by other instruments during selected periods of time, we apply this relation to the spacecraft potential measured continuously from 1977 to 1984 on ISEE-1. An image of the plasma density in the magnetosphere and its environment is obtained as a result. All principal magnetospheric regions are clearly identified, from the solar wind with a density around 5 cm-3 , the magnetosheath around 50 cm-3, the magnetosphere around 1 cm-3, the plasma sheet around 0.5 cm-3 and finally the more tenuous tail lobes below 0.1 cm-3. The plasma density was observed slightly higher on the dawnside than on the dusk side of the magnetosphere. In addition the magnetosheath was closer to the Earth on the dawnside than on the duskside. When the magnetic activity increased (recorded by the AE index), the dayside magnetosphere was compressed/eroded by about 1 to 2 RE while the plasmasphere/inner magnetosphere became quite irregular and expanded in the dawn-midnight and in the dusk-noon sectors. In addition, during high magnetic activity, the plasmasheet at Ygsm = 0 was thicker and denser than at low activity. On the other hand the flanks of the plasmasheet were thinner and less dense during high activity than during low activity.
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| 3. |
- Genestreti, K. J., et al.
(författare)
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MMS Observation of Asymmetric Reconnection Supported by 3-D Electron Pressure Divergence
- 2018
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Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 123:3, s. 1806-1821
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Tidskriftsartikel (refereegranskat)abstract
- We identify the electron diffusion region (EDR) of a guide field dayside reconnection site encountered by the Magnetospheric Multiscale (MMS) mission and estimate the terms in generalized Ohm's law that controlled energy conversion near the X-point. MMS crossed the moderate-shear (similar to 130 degrees) magnetopause southward of the exact X-point. MMS likely entered the magnetopause far from the X-point, outside the EDR, as the size of the reconnection layer was less than but comparable to the magnetosheath proton gyroradius, and also as anisotropic gyrotropic "outflow" crescent electron distributions were observed. MMS then approached the X-point, where all four spacecraft simultaneously observed signatures of the EDR, for example, an intense out-of-plane electron current, moderate electron agyrotropy, intense electron anisotropy, nonideal electric fields, and nonideal energy conversion. We find that the electric field associated with the nonideal energy conversion is (a) well described by the sum of the electron inertial and pressure divergence terms in generalized Ohms law though (b) the pressure divergence term dominates the inertial term by roughly a factor of 5:1, (c) both the gyrotropic and agyrotropic pressure forces contribute to energy conversion at the X-point, and (d) both out-of-the-reconnection-plane gradients (partial derivative/partial derivative M) and in-plane (partial derivative/partial derivative L, N) in the pressure tensor contribute to energy conversion near the X-point. This indicates that this EDR had some electron-scale structure in the out-of-plane direction during the time when (and at the location where) the reconnection site was observed.
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| 4. |
- Hadid, L. Z., et al.
(författare)
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BepiColombo's Cruise Phase : Unique Opportunity for Synergistic Observations
- 2021
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Ingår i: Frontiers in Astronomy and Space Sciences. - : Frontiers Media S.A.. - 2296-987X. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- The investigation of multi-spacecraft coordinated observations during the cruise phase of BepiColombo (ESA/JAXA) are reported, with a particular emphasis on the recently launched missions, Solar Orbiter (ESA/NASA) and Parker Solar Probe (NASA). Despite some payload constraints, many instruments onboard BepiColombo are operating during its cruise phase simultaneously covering a wide range of heliocentric distances (0.28 AU-0.5 AU). Hence, the various spacecraft configurations and the combined in-situ and remote sensing measurements from the different spacecraft, offer unique opportunities for BepiColombo to be part of these unprecedented multipoint synergistic observations and for potential scientific studies in the inner heliosphere, even before its orbit insertion around Mercury in December 2025. The main goal of this report is to present the coordinated observation opportunities during the cruise phase of BepiColombo (excluding the planetary flybys). We summarize the identified science topics, the operational instruments, the method we have used to identify the windows of opportunity and discuss the planning of joint observations in the future.
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| 5. |
- Hwang, K-J, et al.
(författare)
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Magnetic Reconnection Inside a Flux Rope Induced by Kelvin-Helmholtz Vortices
- 2020
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Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 125:4
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Tidskriftsartikel (refereegranskat)abstract
- On 5 May 2017, MMS observed a crater-type flux rope on the dawnside tailward magnetopause with fluctuations. The boundary-normal analysis shows that the fluctuations can be attributed to nonlinear Kelvin-Helmholtz (KH) waves. Reconnection signatures such as flow reversals and Joule dissipation were identified at the leading and trailing edges of the flux rope. In particular, strong northward electron jets observed at the trailing edge indicated midlatitude reconnection associated with the 3-D structure of the KH vortex. The scale size of the flux rope, together with reconnection signatures, strongly supports the interpretation that the flux rope was generated locally by KH vortex-induced reconnection. The center of the flux rope also displayed signatures of guide-field reconnection (out-of-plane electron jets, parallel electron heating, and Joule dissipation). These signatures indicate that an interface between two interlinked flux tubes was undergoing interaction, causing a local magnetic depression, resulting in an M-shaped crater flux rope, as supported by reconstruction.
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| 6. |
- Hwang, K. -J, et al.
(författare)
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Microscale Processes Determining Macroscale Evolution of Magnetic Flux Tubes along Earth's Magnetopause
- 2021
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Ingår i: Astrophysical Journal. - : Institute of Physics Publishing (IOPP). - 0004-637X .- 1538-4357. ; 914:1
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Tidskriftsartikel (refereegranskat)abstract
- An important process affecting solar wind-Earth's magnetosphere coupling is nonsteady dayside magnetic reconnection, observationally evidenced by a flux transfer event (FTE) that shows a bipolar variation of the magnetic field component normal to the magnetopause. FTEs often consist of two interlinked flux tubes, but, local kinetic processes between the flux tubes are not understood in the context of the FTE structuring, evolution, and impact. An FTE observed by the Magnetospheric Multiscale mission on 2017 December 18 consisted of two flux tubes of different topology. One includes field lines with ends connected to the northern and southern hemispheres while the other includes field lines with both ends connected to the magnetosheath. Reconnection occurring at the flux-tube interface indicates how interacting flux tubes evolve into a flux rope with helical magnetic topology that is either closed or open. This study demonstrates a new aspect of how micro- to meso-scale dynamics occurring within FTEs determines their macroscale characteristics and evolution.
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| 7. |
- Li, B., et al.
(författare)
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Magnetospheric Multiscale Observations of ULF Waves and Correlated Low-Energy Ion Monoenergetic Acceleration
- 2019
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Ingår i: Journal of Geophysical Research - Space Physics. - : Blackwell Publishing Ltd. - 2169-9380 .- 2169-9402.
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Tidskriftsartikel (refereegranskat)abstract
- Low-energy ions of ionospheric origin with energies below 10s of electron volt dominate most of the volume and mass of the terrestrial magnetosphere. However, sunlit spacecraft often become positively charged to several 10s of volts, which prevents low-energy ions from reaching the particle detectors on the spacecraft. Magnetospheric Multiscale spacecraft (MMS) observations show that ultralow-frequency (ULF) waves drive low-energy ions to drift in the E × B direction with a drift velocity equal to V E × B , and low-energy ions were accelerated to sufficient total energy to be measured by the MMS/Fast Plasma Investigation Dual Ion Spectrometers. The maximum low-energy ion energy flux peak seen in MMS1's dual ion spectrometer measurements agreed well with the theoretical calculation of H + ion E × B drift energy. The density of ions in the energy range below minimum energy threshold was between 1 and 3 cm −3 in the magnetosphere subsolar region in this event.
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| 8. |
- Nakamura, R., et al.
(författare)
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Initial Results From the Active Spacecraft Potential Control Onboard Magnetospheric Multiscale Mission
- 2017
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Ingår i: IEEE Transactions on Plasma Science. - : Institute of Electrical and Electronics Engineers (IEEE). - 0093-3813 .- 1939-9375. ; 45:8, s. 1847-1852
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Tidskriftsartikel (refereegranskat)abstract
- NASA's magnetospheric multiscale (MMS) mission was successfully launched in March 2015. The scientific objectives of MMS are to explore and understand fundamental plasma physics processes in the earth's magnetosphere: magnetic reconnection, particle acceleration, and turbulence. The region of scientific interest of MMS is in a tenuous plasma environment where the positive spacecraft potential may reach an equilibrium as high as several tens of volts. The active spacecraft potential control (ASPOC) instrument neutralizes the spacecraft potential by releasing the positive charge produced by indium ion emitters. While the method has successfully been applied to other spacecraft such as Cluster and Double Star, new developments in the design of the emitters and the electronics are enabling lower spacecraft potentials and higher reliability compared to previous missions. In this paper, we report the initial results from the tests of the ASPOC performance during the commissioning phase and discuss the different effects on the particle and field instruments observed at different plasma environments in the magnetosphere.
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| 9. |
- Nakamura, R., et al.
(författare)
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Thin Current Sheet Behind the Dipolarization Front
- 2021
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Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 126:10
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Tidskriftsartikel (refereegranskat)abstract
- We report a unique conjugate observation of fast flows and associated current sheet disturbances in the near-Earth magnetotail by MMS (Magnetospheric Multiscale) and Cluster preceding a positive bay onset of a small substorm at similar to 14:10 UT, September 8, 2018. MMS and Cluster were located both at X similar to -14 R-E. A dipolarization front (DF) of a localized fast flow was detected by Cluster and MMS, separated in the dawn-dusk direction by similar to 4 R-E,R- almost simultaneously. Adiabatic electron acceleration signatures revealed from the comparison of the energy spectra confirm that both spacecraft encounter the same DF. We analyzed the change in the current sheet structure based on multi-scale multi-point data analysis. The current sheet thickened during the passage of DF, yet, temporally thinned subsequently associated with another flow enhancement centered more on the dawnward side of the initial flow. MMS and Cluster observed intense perpendicular and parallel current in the off-equatorial region mainly during this interval of the current sheet thinning. Maximum field-aligned currents both at MMS and Cluster are directed tailward. Detailed analysis of MMS data showed that the intense field-aligned currents consisted of multiple small-scale intense current layers accompanied by enhanced Hall-currents in the dawn-dusk flow-shear region. We suggest that the current sheet thinning is related to the flow bouncing process and/or to the expansion/activation of reconnection. Based on these mesoscale and small-scale multipoint observations, 3D evolution of the flow and current-sheet disturbances was inferred preceding the development of a substorm current wedge.
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| 10. |
- Orsini, S., et al.
(författare)
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Inner southern magnetosphere observation of Mercury via SERENA ion sensors in BepiColombo mission
- 2022
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Ingår i: Nature Communications. - : Nature Publishing Group. - 2041-1723. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- Mercury’s southern inner magnetosphere is an unexplored region as it was not observed by earlier space missions. In October 2021, BepiColombo mission has passed through this region during its first Mercury flyby. Here, we describe the observations of SERENA ion sensors nearby and inside Mercury’s magnetosphere. An intermittent high-energy signal, possibly due to an interplanetary magnetic flux rope, has been observed downstream Mercury, together with low energy solar wind. Low energy ions, possibly due to satellite outgassing, were detected outside the magnetosphere. The dayside magnetopause and bow-shock crossing were much closer to the planet than expected, signature of a highly eroded magnetosphere. Different ion populations have been observed inside the magnetosphere, like low latitude boundary layer at magnetopause inbound and partial ring current at dawn close to the planet. These observations are important for understanding the weak magnetosphere behavior so close to the Sun, revealing details never reached before.
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