100 research outputs found
Contributed Review: Absolute spectral radiance calibration of fiber-optic shock-temperature pyrometers using a coiled-coil irradiance standard lamp
Self-consistent Coronal Heating and Solar Wind Acceleration from Anisotropic Magnetohydrodynamic Turbulence
We present a series of models for the plasma properties along open magnetic
flux tubes rooted in solar coronal holes, streamers, and active regions. These
models represent the first self-consistent solutions that combine: (1)
chromospheric heating driven by an empirically guided acoustic wave spectrum,
(2) coronal heating from Alfven waves that have been partially reflected, then
damped by anisotropic turbulent cascade, and (3) solar wind acceleration from
gradients of gas pressure, acoustic wave pressure, and Alfven wave pressure.
The only input parameters are the photospheric lower boundary conditions for
the waves and the radial dependence of the background magnetic field along the
flux tube. For a single choice for the photospheric wave properties, our models
produce a realistic range of slow and fast solar wind conditions by varying
only the coronal magnetic field. Specifically, a 2D model of coronal holes and
streamers at solar minimum reproduces the latitudinal bifurcation of slow and
fast streams seen by Ulysses. The radial gradient of the Alfven speed affects
where the waves are reflected and damped, and thus whether energy is deposited
below or above the Parker critical point. As predicted by earlier studies, a
larger coronal ``expansion factor'' gives rise to a slower and denser wind,
higher temperature at the coronal base, less intense Alfven waves at 1 AU, and
correlative trends for commonly measured ratios of ion charge states and
FIP-sensitive abundances that are in general agreement with observations. These
models offer supporting evidence for the idea that coronal heating and solar
wind acceleration (in open magnetic flux tubes) can occur as a result of wave
dissipation and turbulent cascade. (abridged abstract)Comment: 32 pages (emulateapj style), 18 figures, ApJ Supplement, in press (v.
171, August 2007
Evidence for electron Landau damping in space plasma turbulence
How turbulent energy is dissipated in weakly collisional space and astrophysical plasmas is a major open question. Here, we present the application of a field-particle correlation technique to directly measure the transfer of energy between the turbulent electromagnetic field and electrons in the Earth's magnetosheath, the region of solar wind downstream of the Earth's bow shock. The measurement of the secular energy transfer from the parallel electric field as a function of electron velocity shows a signature consistent with Landau damping. This signature is coherent over time, close to the predicted resonant velocity, similar to that seen in kinetic Alfven turbulence simulations, and disappears under phase randomisation. This suggests that electron Landau damping could play a significant role in turbulent plasma heating, and that the technique is a valuable tool for determining the particle energisation processes operating in space and astrophysical plasmas.STFC Ernest Rutherford Fellowship [ST/N003748/2]; NASA HSR grant [NNX16AM23G]; NSF CAREER Award [AGS-1054061]; NASA HGI grant [80NSSC18K0643]; NASA MMS GI grant [80NSSC18K1371]Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
Magnetohydrodynamic Oscillations in the Solar Corona and Earth’s Magnetosphere: Towards Consolidated Understanding
Stability of magnetic configurations in the solar atmosphere under temperature anisotropy conditions
Reliability and flexibility in a system consisting of coke batteries and exhaust-gas processing units
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