4 research outputs found
Phase mixing of standing Alfven waves with shear flows in solar spicules
Alfvenic waves are thought to play an important role in coronal heating and
solar wind acceleration. Here we investigate the dissipation of such waves due
to phase mixing at the presence of shear flow and field in the stratified
atmosphere of solar spicules. The initial flow is assumed to be directed along
spicule axis and to vary linearly in the x direction and the equilibrium
magnetic field is taken 2-dimensional and divergence-free. It is determined
that the shear flow and field can fasten the damping of standing Alfven waves.
In spite of propagating Alfven waves, standing Alfven waves in Solar spicules
dissipate in a few periods. As height increases, the perturbed velocity
amplitude does increase in contrast to the behavior of perturbed magnetic
field. Moreover, it should be emphasized that the stratification due to
gravity, shear flow and field are the facts that should be considered in MHD
models in spicules.Comment: Accepted for publication in Astrophysics & Space Scienc
Origins of the Ambient Solar Wind: Implications for Space Weather
The Sun's outer atmosphere is heated to temperatures of millions of degrees,
and solar plasma flows out into interplanetary space at supersonic speeds. This
paper reviews our current understanding of these interrelated problems: coronal
heating and the acceleration of the ambient solar wind. We also discuss where
the community stands in its ability to forecast how variations in the solar
wind (i.e., fast and slow wind streams) impact the Earth. Although the last few
decades have seen significant progress in observations and modeling, we still
do not have a complete understanding of the relevant physical processes, nor do
we have a quantitatively precise census of which coronal structures contribute
to specific types of solar wind. Fast streams are known to be connected to the
central regions of large coronal holes. Slow streams, however, appear to come
from a wide range of sources, including streamers, pseudostreamers, coronal
loops, active regions, and coronal hole boundaries. Complicating our
understanding even more is the fact that processes such as turbulence,
stream-stream interactions, and Coulomb collisions can make it difficult to
unambiguously map a parcel measured at 1 AU back down to its coronal source. We
also review recent progress -- in theoretical modeling, observational data
analysis, and forecasting techniques that sit at the interface between data and
theory -- that gives us hope that the above problems are indeed solvable.Comment: Accepted for publication in Space Science Reviews. Special issue
connected with a 2016 ISSI workshop on "The Scientific Foundations of Space
Weather." 44 pages, 9 figure