A5004940654- Solar and Space Plasma Dynamics
- Ionosphere and magnetosphere dynamics
- Astro and Planetary Science
- Astrophysics and Cosmic Phenomena
- Gamma-ray bursts and supernovae
- Atmospheric Ozone and Climate
- Solar Radiation and Photovoltaics
- Geomagnetism and Paleomagnetism Studies
- Stellar, planetary, and galactic studies
- Dark Matter and Cosmic Phenomena
- Geophysics and Gravity Measurements
- Magnetic confinement fusion research
- Fluid Dynamics and Turbulent Flows
- Cosmology and Gravitation Theories
- Astrophysics and Star Formation Studies
- Advanced Thermodynamics and Statistical Mechanics
- Earthquake Detection and Analysis
- Tropical and Extratropical Cyclones Research
- Spacecraft and Cryogenic Technologies
- Combustion and Detonation Processes
- Particle Dynamics in Fluid Flows
- Statistical Mechanics and Entropy
- Radiation Therapy and Dosimetry
- Nuclear Physics and Applications
- Particle Detector Development and Performance
University of Alabama in Huntsville
2014-2023
University of Alabama
2009
University of California, Riverside
2002-2008
University of Delaware
1999-2001
University of Maryland, College Park
1992-1999
Goddard Space Flight Center
1992
North-West University
1989-1990
An emerging paradigm for the dissipation of magnetic turbulence in supersonic solar wind is via localized small-scale reconnection processes, essentially between quasi-2D interacting islands. Charged particles trapped merging islands can be accelerated by electric field generated island and contraction We derive a gyrophase-averaged transport equation experiencing pitch-angle scattering energization super-Alfvénic flowing plasma multiple events. A simpler advection–diffusion nearly isotropic...
Shock waves, as shown by simulations and observations, can generate high levels of downstream vortical turbulence, including magnetic islands. We consider a combination diffusive shock acceleration (DSA) magnetic-island-reconnection-related processes an energization mechanism for charged particles. Observations electron ion distributions interplanetary shocks the heliospheric termination (HTS) are frequently inconsistent with predictions classical DSA. utilize recently developed transport...
In this paper we investigate heliosheath energetic neutral atom (ENA) fluxes at keV energies, by assuming that the proton distribution can be approximated using a κ-distribution. The choice of κ-parameter derives from observational data solar wind (SW). Our work has direct applications to upcoming IBEX mission, since generate all-sky ENA maps within energy range (10 eV-6 keV), as well spectra in several directions. We find use κ, opposed Maxwellian, gives rise greatly increased above 1 keV,...
Simulations of particle acceleration in turbulent plasma regions with multiple contracting and merging (reconnecting) magnetic islands emphasize the key role temporary trapping island structures for efficient particles to form hard power-law spectra. Statistical kinetic transport theories have been developed that capture essential physics multi-island regions. The theory Zank et al. is further by considering effects both mean variance electric fields induced dynamics inertial-scale flux...
Increases of ion fluxes in the keV-MeV range are sometimes observed near heliospheric current sheet (HCS) during periods when other sources absent. These resemble solar energetic particle (SEP) events, but events weaker and apparently local. Conventional explanations based on either shock acceleration charged particles or due to magnetic reconnection at interplanetary sheets not persuasive. We suggest instead that recurrent occurs HCS smaller wind (Zharkova & Khabarova 2012), which a...
We explore the role of heliospheric magnetic field configurations and conditions that favor generation confinement small-scale islands associated with atypical energetic particle events (AEPEs) in solar wind. Some AEPEs do not align standard acceleration mechanisms, such as flare-related or simple diffusive shock processes related to interplanetary coronal mass ejections (ICMEs) corotating interaction regions (CIRs). As we have shown recently, flux enhancements may well originate locally can...
The problem of perpendicular diffusion by a particle in turbulent plasma is enduring interest and one that has yet to be fully solved. Analytic models do not agree with either observations or numerical simulations. Recently, nonlinear guiding center theory (NLGC) was developed Matthaeus et al. [2003] which, for the first time, appears consistent simulations both high‐energy low‐energy regimes, provided transverse magnetic field complex. Flux surfaces high complexity are characterized rapid...
A Chapman-Kolmogorov equation description of compound transport cosmic rays due to random walk the magnetic field lines, and for a range models particle along field, is developed. The probability distribution, Pp, propagation corresponds either (1) ballistic or scatter-free model, (2) parallel diffusion (3) telegrapher model. distribution function (pdf) describing statistics, PFRW, assumed be Gaussian. These are used discuss features dropout events in low-energy, solar cosmic-ray intensity...
Abstract Drift effects play a significant role in the transport of charged particles heliosphere. A turbulent magnetic field is also known to reduce particle drifts. The exact nature this reduction, however, not clear. This study aims provide some insight into reduction and proposes relatively simple, tractable means modeling it that provides results reasonable agreement with numerical simulations drift coefficient field.
Abstract An observational analysis of an atypical energetic particle event near 5 au measured by the Ulysses spacecraft is presented. A previous study has attributed unusual enhancement proton flux to presence small-scale dynamic magnetic islands or ropes. Here, we find that generation these may be related interaction a stream region (SIR) and heliospheric current sheet (HCS). Particles are accelerated trapped within SIR structure characterized forward shock–reverse wave pair. Analysis...
view Abstract Citations (96) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Simulation of Complete 11 and 22 Year Modulation Cycles for Cosmic Rays in the Heliosphere Using a Drift Model with Global Merged Interaction Regions Le Roux, J. A. ; Potgieter, M. S. Two-dimensional, time-dependent drift models have done exceptionally well explaining major modulation features, especially during A less than 0 magnetic polarity cycle heliospheric...
Abstract Previous application of our focused transport equation for energetic ion test particle acceleration by numerous active small-scale flux ropes to solar wind conditions near 1 au yielded the formation hard power-law spectra with high pressure. We present an extended theory where is coupled a new MHD turbulence coherent, quasi-2D magnetic island structures, based on nearly incompressible (N i ) theory. The latter includes expressions damping/growth rates that enable self-consistent...
ABSTRACT Computational and observational evidence is accruing that heliospheric shocks, as emitters of vorticity, can produce downstream magnetic flux ropes filaments. This led Zank et al. to investigate a new paradigm whereby energetic particle acceleration near shocks combination diffusive shock (DSA) with by many small-scale contracting reconnecting (merging) ropes. Using model where flux-rope involves first-order Fermi mechanism due the mean compression numerous ropes, provide...
Abstract One of the curious observations from Voyagers is that intensity anomalous cosmic rays (ACRs) did not peak at heliospheric termination shock (HTS) but instead a short distance (within ∼1 au) downstream HTS. possible explanation interaction wavy current sheet with HTS enhances magnetic reconnection and generates numerous small-scale flux ropes in heliosheath immediately Charged particles are accelerated this region due to Fermi acceleration electric field. In work, we provide...
Abstract With the onset of solar maximum and expected increased prevalence interplanetary shock waves, Parker Solar Probe is likely to observe numerous shocks in next few years. An outstanding question that has received surprisingly little attention been how turbulence interacts with collisionless waves. Turbulence supersonic wind described frequently as a superposition majority 2D minority slab component. We formulate collisional perpendicular shock-turbulence transmission problem way...
Standard transport theory is used to investigate the acceleration and modulation of anomalous cosmic rays during solar minimum periods. With developed ray model, pickup ions are transformed into by diffusive shock at heliospheric termination shock. The emphasis on explaining 1987 spectra large radial distances in equatorial plane. Energy density calculations suggest that might be strongly mediated rays. Therefore, spirit nonlinear theory, modeled as a hyperbolic tangent. Calculations show...
We have used steady state modulation models of increasing complexity, with emphasis on drift models, to establish what extent these can simulate the observed cosmic ray integral radial gradient (energy ≥60–70 MeV/nucleon) in heliosphere from 1977 1986. Special attention has been given apparent asymmetric behavior respect recent interplanetary magnetic field polarity reversal, and remarkable constant for years 1977–1982. Instead using differential intensities at specific energies, we...
A time-dependent focused transport approach to modeling diffusive shock acceleration of interstellar pickup ions at the termination is discussed. By taking into account time variations in magnetic field angle, and thus by implication obliquity injection speed using Voyager 1 observations as guide, we show that unaccelerated core protons can be accelerated nearly perpendicular heliospheric nose. Many features anomalous cosmic rays, observed spacecraft energies below big spectral dip starting...
Abstract Recent studies of particle acceleration in the heliosphere have revealed a new mechanism that can locally energize particles up to several MeV nucleon –1 . Stream–stream interactions, as well heliospheric current sheet (CS)—stream lead formation large magnetic cavities, bordered by strong CSs, which turn produce secondary CSs and dynamical small-scale islands (SMIs) ∼0.01 au or less owing reconnection. It has been shown reacceleration occurs via stochastic reconnection SMIs confined...
The theory for the perpendicular diffusion of cosmic rays is not well understood which hampers our understanding ray modulation. In this paper, a spherically symmetric modulation model used to evaluate three different theories in ecliptic plane, subject limitation negligible transport polar direction. models component, it assumed that due large‐scale field line wandering dominates resonant diffusion. To test these models, observations anomalous and galactic helium obtained during time...
view Abstract Citations (71) References (26) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Simulated Features of Heliospheric Cosmic-Ray Modulation with a Time-dependent Drift Model. I. General Effects the Changing Neutral Sheet over Period 1985--1990 Potgieter, M. S. ; Le Roux, J. A. A time-dependent drift model is used to simulate heliospheric modulation galactic cosmic rays, emphasis on effects wavy neutral sheet (HNS) as function time during period...
view Abstract Citations (69) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Time-dependent Drift Model for the Long-Term Modulation of Cosmic Rays with Special Reference to Asymmetries Respect Solar Minimum 1987 Le Roux, J. A. ; Potgieter, M. S. We have developed a time-dependent drift model simulated wavy neutral sheet in which changes waviness propagate radially outward at solar wind velocity. Using an asymmetric rate change tilt angle,...