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Recent numerical investigations of wave propagation near coronal magnetic
null points (McLaughlin and Hood: Astron. Astrophys. 459, 641,2006) have
indicated how a fast MHD wave partially converts into a slow MHD wave as the
disturbance passes from a low-beta plasma to a high-beta plasma. This is a
complex process and a clear understanding of the conversion mechanism requires
the detailed investigation of a simpler model. An investigation of mode
conversion in a stratified, isothermal atmosphere, with a uniform, vertical
magnetic field is carried out, both numerically and analytically. In contrast
to previous investigations of upward-propagating waves (Zhugzhda and Dzhalilov:
Astron. Astrophys. 112, 16, 1982a; Cally: Astrophys. J. 548, 473, 2001), this
paper studies the downward propagation of waves from a low-beta to high-beta
environment. A simple expression for the amplitude of the transmitted wave is
compared with the numerical solution.Comment: 14 pages, 6 figure
The rapid analysis of ongoing gravitational microlensing events has been integral to the successful detection and characterisation of cool planets orbiting low mass stars in the Galaxy. In this paper we present an implementation of search and fit techniques on Graphical Processing Unit hardware. The method allows for the rapid identification of candidate planetary microlensing events and their subsequent followup for detailed characterisation.
Mode conversion in the region where the sound and Alfven speeds are equal is
a complex process, which has been studied both analytically and numerically,
and has been seen in observations. In order to further the understanding of
this process we set up a simple, one-dimensional model, and examine wave
propagation through this system using a combination of analytical and numerical
techniques. Simulations are carried out in a gravitationally stratified
atmosphere with a uniform, vertical magnetic field for both isothermal and
non-isothermal cases. For the non-isothermal case a temperature profile is
chosen to mimic the steep temperature gradient encountered at the transition
region. In all simulations, a slow wave is driven on the upper boundary, thus
propagating down from low-beta to high-beta plasma across the mode-conversion
region. In addition, a detailed analytical study is carried out where we
predict the amplitude and phase of the transmitted and converted components of
the incident wave as it passes through the mode-conversion region. A comparison
of these analytical predictions with the numerical results shows good
agreement, giving us confidence in both techniques. This knowledge may be used
to help determine wave types observed and give insight into which modes may be
involved in coronal heating.Comment: 7 pages, 5 figure
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