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Vasquez, Bernard J

Publications and source records attributed to Vasquez, Bernard J.

7 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

THE TURBULENT CASCADE AND PROTON HEATING IN THE SOLAR WIND DURING SOLAR MINIMUM

The recently protracted solar minimum provided years of interplanetary data that were largely absent in any association with observed large-scale transient behavior on the Sun. With large-scale shear at 1 AU generally isolated to corotating interaction regions, it is reasonable to ask whether the solar wind is significantly turbulent at this time. We perform a series of third-moment analyses using data from the Advanced Composition Explorer. We show that the solar wind at 1 AU is just as turbulent as at any other time in the solar cycle. Specifically, the turbulent cascade of energy scales in the same manner proportional to the product of wind speed and temperature. Energy cascade rates during solar minimum average a factor of 2-4 higher than during solar maximum, but we contend that this is likely the result of having a different admixture of high-latitude sources.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

VELOCITY POWER SPECTRA FROM CROSS-FIELD TURBULENCE IN THE PROTON KINETIC REGIME

Numerical hybrid simulations with particle protons and fluid electrons are conducted for turbulent fluctuations with spatial variations in a plane perpendicular to the background magnetic field. In the turbulent phase, the proton bulk velocity spectrum has a dissipation range starting at a smaller wavenumber than the magnetic spectrum dissipation range. The steepened portion of the proton bulk velocity spectrum is constrained to a smaller wavenumber with an increasing ratio of background proton plasma to magnetic pressure {beta}{sub p}. The form of the magnetic spectrum does not depend on {beta}{sub p}. The collisionless proton and fluctuation interaction which heats protons mainly across the magnetic field is deemed to be the result of a viscous-like interaction based, in part, on the dependence of the velocity spectrum on {beta}{sub p}.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

OBSERVATIONAL CONSTRAINTS ON THE ROLE OF CYCLOTRON DAMPING AND KINETIC ALFVEN WAVES IN THE SOLAR WIND

Certain few intervals with high-{beta} plasma (ratio of gas pressure to magnetic pressure) have been interpreted as containing turbulent fluctuations with wave vectors that are confined to very oblique angles with respect to the mean magnetic field. The fluctuations are theorized to be Kinetic Alfven Waves (KAWs) engaged in an energy cascade that dissipates primarily at electron scales. Dissipation by ions, and by cyclotron damping in particular, is argued to be minimal to non-existent. This interpretation is not supported, generally, by the analysis of larger data sets using other data analysis methods. These prior studies, however, were not conducted for specific {beta} ranges. In this study, we reconsider the analysis for a moderately large set of high-{beta} intervals. The analysis includes magnetic variance, the Bieber ratio test, the cross-helicity versus magnetic helicity correlation, and the implied break frequency versus angle relationship. In our analysis, the results do not support the exclusive KAW interpretation as applied generally to solar wind intervals of high-{beta} while the results do support the presence of cyclotron damping at a significant level.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

THIRD MOMENTS AND THE ROLE OF ANISOTROPY FROM VELOCITY SHEAR IN THE SOLAR WIND

We have extended the recent analyses of magnetohydrodynamic third moments as they relate to the turbulent energy cascade in the solar wind to consider the effects of large-scale shear flows. Moments from a large set of Advanced Composition Explorer data have been taken, and chosen data intervals are characterized by the rate of change in the solar wind speed. Mean dissipation rates are obtained in accordance with the predictions of homogeneous shear-driven turbulence. Agreement with predictions is best made for rarefaction intervals where the solar wind speed is decreasing with time. For decreasing speed intervals, we find that the dissipation rates increase with increasing shear magnitude and that the shear-induced fluctuation anisotropy is consistent with a relatively small amount.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

A KINETIC MODEL OF SOLAR WIND GENERATION BY OBLIQUE ION-CYCLOTRON WAVES

The fast solar wind is generated by extended perpendicular ion heating in coronal holes, but the kinetic mechanism responsible for this heating has not been determined. One long-standing possibility is the resonant-cyclotron dissipation of ion-cyclotron waves, replenished from a turbulent cascade of interacting counter-propagating Alfven waves. We present results of a kinetic model for proton heating by the quasilinear resonant-cyclotron wave-particle interaction in a coronal hole. The resonant wave spectrum is taken as a power law in wavenumber, uniformly distributed in propagation direction between 0 deg. and 60 deg. with respect to the large-scale radial magnetic field. We obtain the steady-state solution of the kinetic guiding-center equation for the proton distribution in an expanding coronal hole, including the effects of large-scale forces of gravity, charge-separation electric field, Alfven wave ponderomotive force, and mirror force, along with the small-scale scattering from the wave dissipation. We find that plausible wave intensities can yield reasonable flow speeds and temperatures in the heliocentric radial range between 2 and 6 solar radii. We address the claim in earlier work that dissipation of parallel-propagating ion-cyclotron waves cannot provide enough acceleration and show that claim to be incorrect. We find that the combined action of the large-scale forces and the resonant-cyclotron scattering produces proton distribution functions with a characteristic structure: compressed in the sunward half of velocity space with a high-density shell separate from the origin, and relatively expanded in the anti-sunward half of velocity space. We suggest that qualitatively similar proton distributions would result from the kinetic evolution of any sufficiently effective perpendicular heating mechanism operating in an expanding coronal hole.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2010

The effect of spectral anisotropy of fast magnetosonic turbulence on the plasma heating at the proton kinetic scales

The energy transport associated with the fast magnetosonic turbulence in a low-beta plasma is one of the possible driving forces of the solar wind. Two different kinds of the turbulence spectra are discussed in this paper: a unidirectional spectrum of the fluctuations propagating away from the sun and a bidirectional spectrum composed of the sunward and antisunward modes. The evolution of the system is analyzed with the help of hybrid numerical simulations at the proton kinetic scales. It is shown that in the unidirectional case, the heating is always preferentially across the background magnetic field. It is this property that allows the solar wind plasma to be propelled away from the sun by the mirror force of the inhomogeneous magnetic field. Adding the counterpropagating modes reverses the sense of the energy deposition with the parallel heating now dominating the process. However, the parallel heating is produced mostly by fast modes propagating along the magnetic field. If these modes are eliminated, the heating becomes perpendicular again.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2010

Smith et al. Reply:

A Reply to the Comment by J. J. Podesta.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗