93 research outputs found
A New Electric Field in Asymmetric Magnetic Reconnection
We present a theory and numerical evidence for the existence of a previously
unexplored in-plane electric field in collisionless asymmetric magnetic
reconnection. This electric field, dubbed the "Larmor electric field," is
associated with finite Larmor radius effects and is distinct from the known
Hall electric field. Potentially, it could be an important indicator for the
upcoming Magnetospheric Multiscale (MMS) mission to locate reconnection sites
as we expect it to appear on the magnetospheric side, pointing Earthward, at
the dayside magnetopause reconnection site.Comment: 5 pages, 3 figures, to be published in Physical Review Letter
NMDB@Home: 1st virtual symposium on cosmic ray studies with neutron detectors
An overview on the presentations at the first virtual symposium on cosmic ray studies with neutron detectors is given.
The meeting was held online in July 2020. Neutron detectors on ground are shown to provide significant contributions
to research on interactions of galactic cosmic rays with magnetic fields in the Heliosphere and on the acceleration of
energetic particles, as well as to a growing range of applications, including geophysics and space weather. The advent
of easily accessible databases makes original data easily available to a large user community. The present overview
outlines and introduces the more detailed articles contained in the proceedings
NMDB@Athens: Hybrid symposium on cosmic ray studies with neutron detectors
A brief overview is given regarding the presentations delivered at the NMDB@Athens meeting which was held, in a hybrid fashion, in September 2022. Participants joined both remotely but also physically at the National and Kapodistrian University of Athens, Greece. Unlike traditional cosmic ray meetings and conferences where the focus is mainly on the science related to neutron monitor measurements, the ›NMDB@Athens‹ meeting uniquely also addresses hardware issues related to these instruments and, importantly, also databases where different data products can be accessed by a growing and increasingly diverse user base. The present overview outlines and introduces the more detailed articles contained in the proceedings
Complexity and Diffusion of Magnetic Flux Surfaces in Anisotropic Turbulence
The complexity of magnetic flux surfaces is investigated analytically and numerically in static homogeneous magnetic turbulence. Magnetic surfaces are computed to large distances in magnetic fields derived from a reduced magnetohydrodynamic model. The question addressed is whether one can define magnetic surfaces over large distances when turbulence is present. Using a flux surface spectral analysis, we show that magnetic surfaces become complex at small scales, experiencing an exponential thinning that is quantified here. The computation of a flux surface is of either exponential or nondeterministic polynomial complexity, which has the conceptual implication that global identification of magnetic flux surfaces and flux exchange, e.g., in magnetic reconnection, can be intractable in three dimensions. The coarse-grained large-scale magnetic flux experiences diffusive behavior. The link between the diffusion of the coarse-grained flux and field-line random walk is established explicitly through multiple scale analysis. The Kubo number controls both large and small scale limits. These results have consequences for interpreting processes such as magnetic reconnection and field-line diffusion in astrophysical plasmas
Role of Parallel Solenoidal Electric Field on Energy Conversion in 2.5D Decaying Turbulence with a Guide Magnetic Field
We perform 2.5D particle-in-cell simulations of decaying turbulence in the presence of a guide (out-of-plane) background magnetic field. The fluctuating magnetic field initially consists of Fourier modes at low wavenumbers (long wavelengths). With time, the electromagnetic energy is converted to plasma kinetic energy (bulk flow+thermal energy) at the rate per unit volume of J · E for current density J and electric field E . Such decaying turbulence is well known to evolve toward a state with strongly intermittent plasma current. Here we decompose the electric field into components that are irrotational, E ir, and solenoidal (divergence-free), E so. E ir is associated with charge separation, and J · E ir is a rate of energy transfer between ions and electrons with little net change in plasma kinetic energy. Therefore, the net rate of conversion of electromagnetic energy to plasma kinetic energy is strongly dominated by J · E so, and for a strong guide magnetic field, this mainly involves the component E so,∥ parallel to the total magnetic field B . We examine various indicators of the spatial distribution of the energy transfer rate J ∥ · E so,∥, which relates to magnetic reconnection, the best of which are (1) the ratio of the out-of-plane electric field to the in-plane magnetic field, (2) the out-of-plane component of the nonideal electric field, and (3) the magnitude of the estimate of current helicity © 2021. The Author(s). Published by the American Astronomical Society
Observations of Energetic-particle Population Enhancements along Intermittent Structures near the Sun from the Parker Solar Probe
Observations at 1 au have confirmed that enhancements in measured energetic-particle (EP) fluxes are statistically associated with "rough" magnetic fields, i.e., fields with atypically large spatial derivatives or increments, as measured by the Partial Variance of Increments (PVI) method. One way to interpret this observation is as an association of the EPs with trapping or channeling within magnetic flux tubes, possibly near their boundaries. However, it remains unclear whether this association is a transport or local effect; i.e., the particles might have been energized at a distant location, perhaps by shocks or reconnection, or they might experience local energization or re-acceleration. The Parker Solar Probe (PSP), even in its first two orbits, offers a unique opportunity to study this statistical correlation closer to the corona. As a first step, we analyze the separate correlation properties of the EPs measured by the Integrated Science Investigation of the Sun (IS⊙IS) instruments during the first solar encounter. The distribution of time intervals between a specific type of event, i.e., the waiting time, can indicate the nature of the underlying process. We find that the IS⊙IS observations show a power-law distribution of waiting times, indicating a correlated (non-Poisson) distribution. Analysis of low-energy (~15 – 200 keV/nuc) IS⊙IS data suggests that the results are consistent with the 1 au studies, although we find hints of some unexpected behavior. A more complete understanding of these statistical distributions will provide valuable insights into the origin and propagation of solar EPs, a picture that should become clear with future PSP orbits
Solar and Interplanetary Turbulence: Lagrangian Coherent Structures
Talk delivered in 22nd EGU General Assembly, held online 4-8 May, 2020, id.4289, https://meetingorganizer.copernicus.org/EGU2020/EGU2020-4289.html.-- https://www.egu2020.eu/The dynamics of solar and interplanetary plasmas is governed by coherent structures such as current sheets and magnetic flux ropes which are responsible for the genesis of intermittent turbulence via magnetic reconnections in solar supergranular junctions, solar coronal loops, the shock-sheath region of an interplanetary coronal mass ejection, and the interface region of two interplanetary magnetic flux ropes. Lagrangian coherent structures provide a new powerful technique to detect time- or space-dependent transport barriers, and objective (i.e., frame invariant) kinematic and magnetic vortices in space plasma turbulence. We discuss the basic concepts of Lagrangian coherent structures in plasmas based on the computation of the finite-time Lyapunov exponent, the Lagrangian averaged vorticity deviation and the integrated averaged current deviation, as well as their applications to numerical simulations of MHD turbulence and space and ground observations.With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation SEV-2017-070
On the Estimation of Solar Energetic Particle Injection Timing from Onset Times near Earth
We examine the accuracy of a common technique for estimating the start time
of solar energetic particle injection based on a linear fit to the observed
onset time versus 1/(particle velocity). This is based on a concept that the
first arriving particles move directly along the magnetic field with no
scattering. We check this by performing numerical simulations of the transport
of solar protons between 2 and 2000 MeV from the Sun to the Earth, for several
assumptions regarding interplanetary scattering and the duration of particle
injection, and analyzing the results using the inverse velocity fit. We find
that in most cases, the onset times align close to a straight line as a
function of inverse velocity. Despite this, the estimated injection time can be
in error by several minutes. Also, the estimated path length can deviate
greatly from the actual path length along the interplanetary magnetic field.
The major difference between the estimated and actual path lengths implies that
the first arriving particles cannot be viewed as moving directly along the
interplanetary magnetic field.Comment: 19 pages, 3 Postscript figures. Astrophys. J., in pres
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