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- Lotekar, Ajay, et al.
(författare)
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Kinetic-scale Current Sheets in Near-Sun Solar Wind : Properties, Scale-dependent Features and Reconnection Onset
- 2022
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 929:1
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Tidskriftsartikel (refereegranskat)abstract
- We present statistical analysis of 11,200 proton kinetic-scale current sheets (CS) observed by the Parker Solar Probe during 10 days around the first perihelion. The CS thickness lambda is in the range from a few to 200 km with the typical value around 30 km, while current densities are in the range from 0.1 to 10 mu A m(-2) with the typical value around 0.7 mu A m(-2). These CSs are resolved thanks to magnetic field measurements at 73-290 samples s(-1) resolution. In terms of proton inertial length lambda(p), the CS thickness lambda is in the range from about 0.1 to 10 lambda(p) with the typical value around 2 lambda(p). The magnetic field magnitude does not substantially vary across the CSs, and accordingly the current density is dominated by the magnetic-field-aligned component. The CSs are typically asymmetric with statistically different magnetic field magnitudes at the CS boundaries. The current density is larger for smaller-scale CSs, J(0) approximate to 0.15 x (lambda/100 km)(-0.76) mu A m(-2), but does not statistically exceed the Alfven current density J(A) corresponding to the ion-electron drift of the local Alfven speed. The CSs exhibit remarkable scale-dependent current density and magnetic shear angles, J(0)/J(A) approximate to 0.17 x (lambda/lambda(p))(-0.67) and Delta theta approximate to 21 degrees x (lambda/lambda(p))(0.32). Based on these observations and comparison to recent studies at 1 au, we conclude that proton kinetic-scale CSs in the near-Sun solar wind are produced by turbulence cascade, and they are automatically in the parameter range, where reconnection is not suppressed by the diamagnetic mechanism, due to their geometry dictated by turbulence cascade.
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| 2. |
- Lotekar, A., et al.
(författare)
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Multisatellite MMS Analysis of Electron Holes in the Earth's Magnetotail : Origin, Properties, Velocity Gap, and Transverse Instability
- 2020
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Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 125:9
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Tidskriftsartikel (refereegranskat)abstract
- We present a statistical analysis of more than 2,400 electrostatic solitary waves interpreted as electron holes (EH) measured aboard at least three Magnetospheric Multiscale (MMS) spacecraft in the Earth's magnetotail. The velocities of EHs are estimated using the multispacecraft interferometry. The EH velocities in the plasma rest frame are in the range from just a few km/s, which is much smaller than ion thermal velocity V-Ti, up to 20,000 km/s, which is comparable to electron thermal velocity V-Te. We argue that fast EHs with velocities larger than about 0.1V(Te) are produced by bump-on-tail instabilities, while slow EHs with velocities below about 0.05V(Te) can be produced by warm bistream and, probably, Buneman-type instabilities. We show that typically fast and slow EHs do not coexist, indicating that the instabilities producing EHs of different types operate independently. We have identified a gap in the distribution of EH velocities between V-Ti and 2V(Ti), which is considered to be the evidence for self-acceleration (Zhou & Hutchinson, 2018) or ion Landau damping of EHs. Parallel spatial scales and amplitudes of EHs are typically between lambda(D) and 10 lambda(D) and between 10(-3) T-e and 0.1 T-e, respectively. We show that electrostatic potential amplitudes of EHs are below the threshold of the transverse instability and highly likely restricted by the nonlinear saturation criterion of electron streaming instabilities seeding electron hole formation: e Phi(0)less than or similar to me pi(2)d(parallel to)(2), where pi = min(gamma, 1.5 omega(ce)), where gamma is the increment of instabilities seeding EH formation, while pi(ce) is electron cyclotron frequency. The implications of the presented results are discussed.
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| 3. |
- Wang, R., et al.
(författare)
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Multisatellite Observations of Ion Holes in the Earth's Plasma Sheet
- 2022
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 49:8
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Tidskriftsartikel (refereegranskat)abstract
- We present the first observations of electrostatic solitary waves with electrostatic potential of negative polarity around a fast plasma flow in the Earth's plasma sheet. The solitary waves are observed aboard four Magnetospheric Multiscale spacecraft, which allowed accurately estimating solitary wave properties. Based on a data set of 153 solitary waves, we show that they are locally one-dimensional Debye-scale structures with amplitudes up to 20% of local electron temperature and they propagate at plasma frame speeds ranging from a tenth to a few ion-acoustic speeds at arbitrary angles to the local magnetic field. The solitary waves are associated with multi-component proton distributions and their velocities are around those of a beam-like proton population. We argue that the solitary waves are ion holes, nonlinear structures produced by ion-streaming instabilities, and conclude that once ions are not magnetized, ion holes can propagate oblique to local magnetic field.
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