We demonstrate directional output from a deformed disk laser of dimensions comparable to the emission wavelength. Unlike larger deformed cavity lasers, which exhibit universal output directionality ...determined by chaotic ray dynamics, the far-field patterns differ between lasing modes. The directional emission results from weak coupling of isotropic high-quality modes to anisotropic low-quality modes, combined with chiral symmetry breaking of clockwise and counterclockwise propagating waves. This mechanism makes it possible to control the output properties of wavelength-scale lasers.
We investigate the current carriers and current sources of an ion scale tangential magnetopause current layer using the Magnetospheric Multiscale four spacecraft data. Within this magnetopause ...current layer, ions and electrons equally contribute to the perpendicular current, while electrons carry nearly all the parallel current. The energy range of all these current carriers is predominantly from middle to high (>100 eV), where particles with higher energies are more efficient in producing the current. By comparing each term, two‐fluid magnetohydrodynamic (MHD) theory is able to describe the current sources to a large degree because the sum of all the perpendicular currents from MHD theory could account for the currents observed. In addition, we find that the ion diamagnetic current is the main source of the total perpendicular current, while the curvature current can be neglected. Nevertheless, ions and electrons both carry comparable current due to the redistribution of the electric field and show features beyond the classic Chapman‐Ferraro model, particularly on the front side of the boundary layer where the electric field reversal is most intense. We also show a second, comparative event in which ions do not satisfy MHD theory, while the electrons do. The small‐scale, adiabatic parameter (square of curvature radius/gyroradius) supports our interpretation that this second event contains ion scale substructure. We suggest that comparing the predicted MHD current with plasma current can be a good method to judge whether the MHD theory is satisfied in each specific circumstance, especially for high‐precision Magnetospheric Multiscale data.
Key Points
Identification of the current carriers and sources within the magnetopause boundary layer is made
The ion diamagnetic current is found to be the main source of the perpendicular current
Two‐fluid MHD theory is shown to hold for an ion gyroradius scale boundary layer, while it is partly violated for a more complex structure
We investigated the electronic structure of 5d transition-metal oxide Sr2IrO4 using angle-resolved photoemission, optical conductivity, x-ray absorption measurements, and first-principles band ...calculations. The system was found to be well described by novel effective total angular momentum Jeff states, in which the relativistic spin-orbit coupling is fully taken into account under a large crystal field. Despite delocalized Ir 5d states, the Jeff states form such narrow bands that even a small correlation energy leads to the Jeff=1/2 Mott ground state with unique electronic and magnetic behaviors, suggesting a new class of Jeff quantum spin driven correlated-electron phenomena.
Abstract
Energetic electrons have been frequently observed during magnetic reconnection in the magnetotail. The acceleration process of the energetic electrons is not fully understood. In this paper, ...we select for a detailed study a case of energetic electron acceleration from the earlier reported interval of turbulent magnetic reconnection in Earth’s magnetotail observed by the Magnetospheric Multiscale mission. We use the first-order Taylor expansion method to reconstruct the magnetic topology of electron acceleration sites from the data. We find that the energetic electron fluxes increase inside the flux rope forming in front of the magnetic pileup region. We show that the energetic electrons are produced by a two-step process where two different acceleration mechanisms are successively operating outside and inside the flux rope. First, the thermal electrons are energized in the field-aligned direction inside the magnetic pileup region owing to the Fermi mechanism forming a cigar-like distribution. Second, those energized electrons are further accelerated predominately antiparallel to the magnetic field direction by a parallel electric field inside the flux rope. Our findings provide information for a better understanding of the generation of energetic electrons during turbulent reconnection process.
Using the high‐resolution measurements from magnetospheric multiscale mission, here we present the observational evidence of kinetic interchange instabilities (ICIs) at dipolarization fronts (DFs). ...Specifically, we present the observation of two DFs caused by ICI, and discover the sub‐ion scale magnetic depression caused by kinetic‐scale ICI at the second DF. By using multi‐spacecraft observation, the typical process inside the magnetic hole (MH)—by electron trapping process—is clearly shown in the magnetic depression, evidencing that the depression is a sub‐ion MH generated at DF by kinetic ICI. Based on observations and Minimum Variance Analysis (MVA) analysis, we present a two‐dimensional image of the ICI in the nonlinear stage. This observational study demonstrates the kinetic ICI at DFs, confirming the existence of MH generated by ICI at DF, and improves the understanding of dynamics at DFs.
Plain Language Summary
Taking advantage of the high‐resolution measurements from magnetospheric multiscale mission, we present the direct evidence of kinetic interchange instabilities (ICIs) at the dipolarization fronts (DFs). Specifically, two DFs caused by ICI and magnetic depression at the second DF caused by kinetic ICI are observed in our study. By comparing the measurements of three spacecraft, we find that the magnetic depression at second DF can trap the electrons, which is the typical process inside the magnetic hole. We plot a two‐dimensional image to illustrate the ICI at DFs, and the image well fits the observations and the results of Minimum Variance Analysis (MVA) analysis.
Key Points
We present the observational evidence of kinetic interchange instabilities at dipolarization fronts (DFs)
Based on observations and Minimum Variance Analysis (MVA) analysis, we present a 2D image of the interchange instabilities at the DFs
Direct evidence of sub‐ion magnetic hole caused by interchange instabilities at DF
Observations with the Venus Express magnetometer and low-energy particle detector revealed magnetic field and plasma behavior in the near-Venus wake that is symptomatic of magnetic reconnection, a ...process that occurs in Earth's magnetotail but is not expected in the magnetotail of a nonmagnetized planet such as Venus. On 15 May 2006, the plasma flow in this region was toward the planet, and the magnetic field component transverse to the flow was reversed. Magnetic reconnection is a plasma process that changes the topology of the magnetic field and results in energy exchange between the magnetic field and the plasma. Thus, the energetics of the Venus magnetotail resembles that of the terrestrial tail, where energy is stored and later released from the magnetic field to the plasma.
Dipolarization fronts (DFs) have been documented as important structures contributing to energy conversion and flux transport in Earth's magnetotail. However, energy partition and balance at DFs ...still remain elusive. Using high‐cadence data from NASA's Magnetospheric Multiscale mission, we preform a comprehensive investigation of energy budgets at the DFs. We find that material derivatives of particle energy densities in the DF frame are basically close to zero, indicating that particles experience negligible heating and/or acceleration and that the energy released at the DFs is predominantly manifested in the form of energy flux. The energy flux is found to be dominated by ion and electron enthalpy flux, ion heat flux, and Poynting flux, with electron enthalpy flux being locally elevated. In addition, the energy flux tends to increase during the DFs' earthward propagation, without exhibiting clear asymmetry in the dawn‐dusk direction. These results help further understand energy budgets at the DFs.
Plain Language Summary
Dipolarization fronts (DFs), earthward‐propagating magnetic structures characterized by sharp enhancement of northward component (Bz) of the geomagnetic field, have been suggested as favorable regions for particle acceleration/heating, wave generation, and energy transport, etc. In particular, DFs host significant local energy conversion processes which might be responsible for the global energy transport in the Earth's magnetotail. Therefore they have attracted considerable interest in the recent two decades. In the present study, we aim to investigate one key issue regarding energy conversion at the DFs, that is, energy partition and balance, by taking advantage of unprecedentedly high‐cadence data from the NASA's Magnetospheric Multiscale mission. New results obtained from the present investigation can help better understand energy budgets at the fronts and its role in global energy transport.
Key Points
Energy released at dipolarization fronts (DFs) is predominately manifested in the form of energy flux, without significant particle heating and/or acceleration
Energy flux is dominated by particle enthalpy flux, ion heat flux and Poynting flux, with electron enthalpy flux locally elevated
Energy flux tends to increase during DFs' earthward propagation, without clear asymmetry in the dawn‐dusk direction
Upgraded electronics, improved water system dynamics, better calibration and analysis techniques allowed Super-Kamiokande-IV to clearly observe very low-energy B8 solar neutrino interactions, with ...recoil electron kinetic energies as low as ∼3.5 MeV. Super-Kamiokande-IV data-taking began in September of 2008; this paper includes data until February 2014, a total livetime of 1664 days. The measured solar neutrino flux is (2.308±0.020(stat)−0.040+0.039(syst))×106/(cm2 sec) assuming no oscillations. The observed recoil electron energy spectrum is consistent with no distortions due to neutrino oscillations. An extended maximum likelihood fit to the amplitude of the expected solar zenith angle variation of the neutrino-electron elastic scattering rate in SK-IV results in a day/night asymmetry of (−3.6±1.6(stat)±0.6(syst))%. The SK-IV solar neutrino data determine the solar mixing angle as sin2θ12=0.327−0.031+0.026, all SK solar data (SK-I, SK-II, SK III and SK-IV) measures this angle to be sin2θ12=0.334−0.023+0.027, the determined mass-squared splitting is Δm212=4.8−0.8+1.5×10−5 eV2.
Abstract
Magnetic discontinuities are fundamental structures in space and laboratory plasmas where the changes in magnetic and velocity fields are constrained by Rankine–Hugoniot relations. Due to ...the absence of precise measurements for particles, some issues therein are hardly investigated. The nature of discontinuities driven by the magnetohydrodynamics (MHD) turbulence, and the intermediate shock are two puzzles to be solved. The MHD turbulence generates numerous discontinuities with both small normal magnetic fields and nearly constant magnetic field magnitudes in statistics. By utilizing the data from the Parker Solar Probe, we identify among the turbulence-driven discontinuities two components that exhibit diverse statistical characteristics of the plasma density, and reveal that these discontinuities comprise 80.2% rotational and 19.8% tangential discontinuities. Then, we note a special class of discontinuities within 0.35 au that have jump conditions similar to that of the rotational discontinuity and the shock simultaneously, including (1) positively correlated jumps in the plasma density and temperature, (2) a small change in the magnetic field magnitude, and (3) opposite tangential magnetic fields on two sides. These features conform to the theoretical intermediate shock, which previous studies have found to not practically exist due to the breakdown of the evolutionary condition. By the conservation law of the mass flux across a boundary, we calculate their propagation speeds and find three intermediate shock candidates with super-Alfvénic upstream and sub-Alfvénic downstream flows. This work can improve our understanding of plasma intermittencies and suggests reassessing conclusions based on ideal MHD Rankine–Hugoniot relations.
Abstract
Minimum variance analysis of the magnetic field (MVAB), among various techniques of planar structure analysis, is most widely used for its numerical simplicity and loose requirements for ...data. Through a large number of studies based on MVAB, a global picture of the solar wind intermittency has been established. However, the huge discrepancy between the results from MVAB and other techniques like timing/triangulation implies that the uncertainty of MVAB is a crucial issue that is not fully understood. Utilizing Cluster data, we establish a data set comprised of 6752 discontinuities, whose orientations are precisely determined by timing, as a benchmark for testing MVAB. We find that the scatter of the MVAB normals around the timing normal can be reduced by elevating the threshold for the eigenvalue ratio
λ
2
/
λ
3
and narrowing the data window to which MVAB is applied. The misidentification of discontinuities with
B
N
/
∣
B
∣
< 0.4, Δ∣
B
∣/∣
B
∣ < 0.2 as rotational discontinuities (RDs, identified by
B
N
/
∣
B
∣
> 0.4, Δ∣
B
∣/∣
B
∣ < 0.2) is proved to be a major and inherent defect of MVAB, which can occur even when
λ
2
/
λ
3
is large. Such a misidentification process is revealed to be related to a special discontinuity geometry. It also explains the false RD predominance reported by previous studies based on MVAB. Finally, we provide advice for the application of MVAB and discuss the possibility of obtaining the real statistical properties of interplanetary discontinuities by using MVAB.
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