A5057492150- Solar and Space Plasma Dynamics
- Ionosphere and magnetosphere dynamics
- Magnetic confinement fusion research
- Geomagnetism and Paleomagnetism Studies
- Astro and Planetary Science
- Fluid Dynamics and Turbulent Flows
- Gamma-ray bursts and supernovae
- Particle Dynamics in Fluid Flows
- Geophysics and Gravity Measurements
- Planetary Science and Exploration
- Earthquake Detection and Analysis
- Plasma Diagnostics and Applications
- Laser-induced spectroscopy and plasma
- Ocean Waves and Remote Sensing
- Astrophysics and Cosmic Phenomena
- Solar Radiation and Photovoltaics
- Gas Dynamics and Kinetic Theory
- Inorganic Fluorides and Related Compounds
- Wind and Air Flow Studies
- Advanced Thermodynamics and Statistical Mechanics
- Particle accelerators and beam dynamics
- Characterization and Applications of Magnetic Nanoparticles
- Geophysics and Sensor Technology
- Cyclone Separators and Fluid Dynamics
- Stellar, planetary, and galactic studies
University of Iowa
2015-2024
Carilion Roanoke Memorial Hospital
2020
Japan External Trade Organization
2015
University of California, Los Angeles
2001-2013
Valdosta State University
2013
Isaac Newton Institute for Mathematical Sciences
2011
University of Maryland, College Park
2010-2011
University of Electro-Communications
2011
University of Hyogo
2011
Dartmouth College
2011
This paper presents a theoretical framework for understanding plasma turbulence in astrophysical plasmas. It is motivated by observations of electromagnetic and density fluctuations the solar wind, interstellar medium galaxy clusters, as well models particle heating accretion disks. All these plasmas many others have turbulent motions at weakly collisional collisionless scales. The focuses on strong mean magnetic field. key assumptions are that small compared to field, spatially anisotropic...
The proton temperature anisotropy in the solar wind is known to be constrained by theoretical thresholds for pressure anisotropy-driven instabilities. Here we use approximately 1 million independent measurements of gyroscale magnetic fluctuations show first time that these are enhanced along mirror, oblique firehose, and ion cyclotron In addition, measured compressibility at high plasma beta ($\beta_\parallel \gtrsim 1$) mirror instability threshold but small elsewhere, consistent with...
This paper studies the turbulent cascade of magnetic energy in weakly collisional magnetized plasmas. A model is presented, based on assumptions local nonlinear transfer wavenumber space, critical balance between linear propagation and interaction times, applicability dissipation rates for nonlinearly plasma. The follows from driving scale MHD regime, through transition at ion Larmor radius into kinetic Alfven wave which turbulence dissipated by processes. fluctuations remain frequencies...
This Letter presents the first ab initio, fully electromagnetic, kinetic simulations of magnetized turbulence in a homogeneous, weakly collisional plasma at scale ion Larmor radius (ion gyroscale). Magnetic- and electric-field energy spectra show break gyroscale; spectral slopes are consistent with scaling predictions for critically balanced Alfvén waves above gyroscale (spectral index -5/3) below indices -7/3 magnetic -1/3 electric fluctuations). behavior is also qualitatively situ...
The nature of small-scale turbulent fluctuations in the solar wind is investigated using a comparison Cluster magnetic and electric field measurements to predictions arising from models consisting either kinetic Alfvén waves or whistler waves. properties these linear theory are used construct spacecraft-frame frequency spectra (|δE|/|δB|)s/c (|δB∥|/|δB|)s/c, allowing for direct spacecraft data. measured fluctuations, found be inconsistent with wave model, agree well prediction spectrum...
A three-dimensional, nonlinear gyrokinetic simulation of plasma turbulence resolving scales from the ion to electron gyroradius with a realistic mass ratio is presented, where all damping provided by resolved physical mechanisms. The resulting energy spectra are quantitatively consistent magnetic power spectrum scaling k(-2.8) as observed in situ spacecraft measurements "dissipation range" solar wind turbulence. Despite strongly nature turbulence, linear kinetic Alfvén wave mode describes...
Magnetohydrodynamic (MHD) turbulence is encountered in a wide variety of astrophysical plasmas, including accretion disks, the solar wind, and interstellar intracluster medium. On small scales, this often expected to consist highly anisotropic fluctuations with frequencies compared ion cyclotron frequency. For number applications, scales are also collisionless, so kinetic treatment necessary. We show that well described by low frequency expansion theory called gyrokinetics. This paper first...
We use a large, statistical set of measurements from the Wind spacecraft at 1 AU, and supporting synthetic data based on kinetic plasma theory, to show that compressible component inertial range solar wind turbulence is primarily in slow mode. The zero-lag cross-correlation C(δn, δB∥) between proton density fluctuations δn field-aligned (compressible) magnetic field δB∥ negative close −1. typical dependence ion beta βi consistent with spectrum wave energy almost entirely This has important...
We present the first study of formation and dissipation current sheets at electron scales in a wave-driven, weakly collisional, three-dimensional kinetic turbulence simulation. investigate relative importance associated with collisionless damping via resonant wave-particle interactions versus small-scale collisional plasma turbulence. Current form self-consistently from wave-driven turbulence, their filling fraction is well correlated to heating rate. However, nature simulation necessarily...
Understanding the physical processes in solar wind and corona which actively contribute to heating, acceleration, dissipation is a primary objective of NASA's Parker Solar Probe (PSP) mission. Observations coherent electromagnetic waves at ion scales suggests that linear cyclotron resonance non-linear are dynamically relevant inner heliosphere. A wavelet-based statistical study first perihelion encounter PSP demonstrates presence transverse resonant observed 30-50\% radial field intervals....
Electrostatic turbulence in weakly collisional, magnetized plasma can be interpreted as a cascade of entropy phase space, which is proposed universal mechanism for dissipation energy turbulence. When the nonlinear decorrelation time at scale thermal Larmor radius shorter than collision time, broad spectrum fluctuations sub-Larmor scales numerically found velocity and position with theoretically predicted scalings. The results are important because they identify what probably Kolmogorov-like...
This paper describes a conceptual framework for understanding kinetic plasma turbulence as generalized form of energy cascade in phase space. It is emphasized that conversion turbulent into thermodynamic heat only achievable the presence some (however small) degree collisionality. The smallness collision rate compensated by emergence small-scale structure velocity For gyrokinetic turbulence, nonlinear perpendicular mixing mechanism identified and described entropy fluctuations simultaneously...
Kinetic plasma theory is used to generate synthetic spacecraft data analyze and interpret the compressible fluctuations in inertial range of solar wind turbulence. The kinetic counterparts three familiar linear MHD wave modes---the fast, Alfven, slow waves---are identified properties density-parallel magnetic field correlation for these modes presented. construction data, based on quasi-linear premise---that some characteristics magnetized turbulence can be usefully modeled as a collection...
The dissipation of turbulence in the weakly collisional solar wind plasma is governed by unknown kinetic mechanisms. Two candidates have been suggested to play an important role dissipation, collisionless damping via wave–particle interactions and small-scale current sheets. High resolution spacecraft measurements turbulent magnetic energy spectrum provide constraints on mechanism. limitations popular fluid hybrid numerical schemes for simulation are discussed, instead a three-dimensional...
A numerical simulation of kinetic plasma turbulence is performed to assess the applicability critical balance kinetic, dissipation scale turbulence. The analysis in frequency domain obviate complications inherent performing a local theoretical model constructed and compared results, excellent agreement found. This result constitutes first evidence provides an anisotropic cascade extending into range. We also perform Eulerian data compare it results previous study magnetohydrodynamic simulations.
The interpretation of single-point spacecraft measurements solar wind turbulence is complicated by the fact that are made in a frame reference relative motion with respect to turbulent plasma. Taylor hypothesis—that temporal fluctuations measured stationary probe rapidly flowing fluid dominated advection spatial structures rest frame—is often assumed simplify analysis. But upcoming missions, such as Solar Probe Plus, threaten violate hypothesis, either due slow flow plasma or dispersive...
How turbulent energy is dissipated in weakly collisional space and astrophysical plasmas a major open question. Here, we present the application of field-particle correlation technique to directly measure transfer between electromagnetic field electrons Earth's magnetosheath, region solar wind downstream bow shock. The measurement secular from parallel electric as function electron velocity shows signature consistent with Landau damping. This coherent over time, close predicted resonant...
Turbulence plays a key role in the conversion of energy large-scale fields and flows to plasma heat, impacting macroscopic evolution heliosphere other astrophysical systems. Although we have long been able make direct spacecraft measurements all aspects electromagnetic field fluctuations near-Earth space, our understanding physical mechanisms responsible for damping turbulent heliospheric plasmas remains incomplete. Here propose an innovative field–particle correlation technique that can be...
One proposed mechanism for heating the solar wind, from close to Sun beyond ∼10 AU, invokes low-frequency, oblique, Alfvén-wave turbulence. Because small-scale oblique Alfvén waves (kinetic waves, KAWs) are compressive, measured density fluctuations in wind place an upper limit on amplitude of KAWs and hence rate at which can be heated by Alfvénic We evaluate this both coronal holes 5 R☉ near-Earth wind. At locations, we find is consistent with models low-frequency 1 turbulent derived within...
The magnetic variance anisotropy ($\mathcal{A}_m$) of the solar wind has been used widely as a method to identify nature turbulent fluctuations; however, thorough discussion meaning and interpretation $\mathcal{A}_m$ not appeared in literature. This paper explores implications limitations using for constraining fluctuation mode composition presents more informative interpreting spacecraft data. also compares predictions from linear theory nonlinear turbulence simulations measurements. In...
A refined cascade model for kinetic turbulence in weakly collisional astrophysical plasmas is presented that includes both the transition between weak and strong effect of nonlocal interactions on nonlinear transfer energy. The describes MHD complementary from Alfvén wave (KAW) to dissipating KAW turbulence, a new regime which effects shearing by large scale motions dissipation play an important role. inclusion energy rate range, specifically large-scale motions, proposed explain nearly...
Motivated by recent observations of distinct parallel and perpendicular signatures in magnetic helicity measurements segregated wave period angle between the local field solar wind velocity, this paper undertakes a comparison three intervals \emph{Ulysses} data with synthetic time series generated from physically motivated turbulence model. From these comparisons, it is hypothesized that observed result cascade \Alfvenic fluctuations local, non-turbulent population ion cyclotron or whistler...