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Articles 31 - 37 of 37
Full-Text Articles in Physical Sciences and Mathematics
The Galactic Center Isolated Nonthermal Filaments As Analogs Of Cometary Plasma Tails, Steven N. Shore, Ted La Rosa
The Galactic Center Isolated Nonthermal Filaments As Analogs Of Cometary Plasma Tails, Steven N. Shore, Ted La Rosa
Faculty Articles
We propose a model for the origin of the isolated nonthermal filaments observed at the Galactic center based on an analogy to cometary plasma tails. We invoke the interaction between a large-scale magnetized galactic wind and embedded molecular clouds. As the advected wind magnetic field encounters a dense molecular cloud, it is impeded and drapes around the cloud, ultimately forming a current sheet in the wake. This draped held is further stretched by the wind flow into a long, thin filament the aspect ratio of which is determined by the balance between the dynamical wind and amplified magnetic field pressures. …
A Dynamical Study Of The Non-Star-Forming Translucent Molecular Cloud Mbm 16: Evidence For Shear-Driven Turbulence In The Interstellar Medium, Ted La Rosa, Steven N. Shore, Loris Magnani
A Dynamical Study Of The Non-Star-Forming Translucent Molecular Cloud Mbm 16: Evidence For Shear-Driven Turbulence In The Interstellar Medium, Ted La Rosa, Steven N. Shore, Loris Magnani
Faculty Articles
We present the results of a velocity correlation study of the high-latitude cloud MBM 16 using a fully sampled 12CO map, supplemented by new 13CO data. We find a correlation length of 0.4 pc. This is similar in size to the formaldehyde clumps described in our previous study. We associate this correlated motion with coherent structures within the turbulent flow. Such structures are generated by free shear flows. Their presence in this non-star-forming cloud indicates that kinetic energy is being supplied to the internal turbulence by an external shear flow. Such large-scale driving over long times is a possible solution …
Production Of Energy-Dependent Time Delays In Impulsive Solar Flare Hard X-Ray Emission By Short-Duration Spectral Index Variations, Ted N. La Rosa, Steven N. Shore
Production Of Energy-Dependent Time Delays In Impulsive Solar Flare Hard X-Ray Emission By Short-Duration Spectral Index Variations, Ted N. La Rosa, Steven N. Shore
Faculty Articles
Cross-correlation techniques have been used recently to study the relative timing of solar flare hard X-ray emission at different energies. These studies find that for the majority of the impulsive flares observed with BATSE there is a systematic time delay of a few tens of milliseconds between low (approximate to 50 keV) and higher energy emission (approximate to 100 keV). These time delays have been interpreted as energy-dependent time-of-flight differences for electron propagation from the corona, where they are accelerated, to the chromosphere, where the bulk of the hard X-rays are emitted. We show in this paper that crosscorrelation methods …
Critical Issues For Understanding Particle Acceleration In Impulsive Solar Flares, James A. Miller, Peter J. Cargill, A. Gordon Emslie, Gordon D. Holman, Brian R. Dennis, Ted N. La Rosa, Robert M. Winglee, Stephen G. Benka, S. Tsuneta
Critical Issues For Understanding Particle Acceleration In Impulsive Solar Flares, James A. Miller, Peter J. Cargill, A. Gordon Emslie, Gordon D. Holman, Brian R. Dennis, Ted N. La Rosa, Robert M. Winglee, Stephen G. Benka, S. Tsuneta
Faculty Articles
This paper, a review of the present status of existing models for particle acceleration during impulsive solar flares, was inspired by a week-long workshop held in the Fall of 1993 at NASA Goddard Space Flight Center. Recent observations from Yohkoh and the Compton Gamma Ray Observatory, and a reanalysis of older observations from the Solar Maximum Mission, have led to important new results concerning the location, timing, and efficiency of particle acceleration in flares. These are summarized in the first part of the review. Particle acceleration processes are then discussed, with;particular emphasis on new developments in stochastic acceleration by magnetohydrodynamic …
New Promise For Electron Bulk Energization In Solar Flares: Preferential Fermi Acceleration Of Electrons Over Protons In Reconnection-Driven Magnetohydrodynamic Turbulence, Ted La Rosa, Ronald L. Moore, James A. Miller, Steven N. Shore
New Promise For Electron Bulk Energization In Solar Flares: Preferential Fermi Acceleration Of Electrons Over Protons In Reconnection-Driven Magnetohydrodynamic Turbulence, Ted La Rosa, Ronald L. Moore, James A. Miller, Steven N. Shore
Faculty Articles
The hard X-ray luminosity of impulsive solar flares indicates that electrons in the low corona are bulk energized to energies of order 25 keV. LaRosa & Moore pointed out that the required bulk energization could be produced by cascading MHD turbulence generated by Alfvénic outflows from sites of strongly driven reconnection. LaRosa, Moore, & Shore proposed that the compressive component of the cascading turbulence dissipates into the electrons via Fermi acceleration. However, for this to be a viable electron bulk energization mechanism, the rate of proton energization by the same turbulence cannot exceed the electron energization rate. In this paper …
Stochastic Electron Acceleration By Cascading Fast Mode Waves In Impulsive Solar Flares, James A. Miller, Ted N. La Rosa, Ronald L. Moore
Stochastic Electron Acceleration By Cascading Fast Mode Waves In Impulsive Solar Flares, James A. Miller, Ted N. La Rosa, Ronald L. Moore
Faculty Articles
We present a model for the acceleration of electrons from thermal to ultrarelativistic energies during an energy release fragment in an impulsive solar flare. Long-wavelength low-amplitude fast mode waves are assumed to be generated during the initial flare energy release (by, for example, large-scale restructuring of the magnetic field). These waves nonlinearly cascade to higher wavenumbers and eventually reach the dissipation range, whereupon they are transit-time damped by electrons in the tail of the thermal distribution. The electrons, in turn, are energized out of the tail and into substantially higher energies. We find that for turbulence energy densities much smaller …
The Wall Of Reconnection-Driven Magnetohydrodynamic Turbulence In A Large Solar-Flare, Ronald L. Moore, Ted N. La Rosa, L. E. Orwig
The Wall Of Reconnection-Driven Magnetohydrodynamic Turbulence In A Large Solar-Flare, Ronald L. Moore, Ted N. La Rosa, L. E. Orwig
Faculty Articles
LaRosa & Moore (1993) recently proposed that the bulk dissipation of magnetic field that is required for the electron energization in the explosive phase of solar flares occurs in a ''fat current sheet,'' a wall of cascading MHD turbulence sustained by highly disordered driven reconnection of opposing magnetic fields impacting at a turbulent boundary layer. In two-ribbon eruptive flares, this turbulent reconnection wall is supposed to develop at the usual reconnection site in the standard model for these flares; that is, the reconnection wall stands in the vertical magnetic rent made by the eruption of the sheared core of the …