60 research outputs found
Spatio-Temporal Scaling of Solar Surface Flows
The Sun provides an excellent natural laboratory for nonlinear phenomena. We
use motions of magnetic bright points on the solar surface, at the smallest
scales yet observed, to study the small scale dynamics of the photospheric
plasma. The paths of the bright points are analyzed within a continuous time
random walk framework. Their spatial and temporal scaling suggest that the
observed motions are the walks of imperfectly correlated tracers on a turbulent
fluid flow in the lanes between granular convection cells.Comment: Now Accepted by Physical Review Letter
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
- …