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Since solar flares are the largest explosions in the solar
system, it isn't surprising that they're often
associated with high-velocity flows. Blobs of ejecta are
frequently observed flying outwards from flares at
speeds of several hundred kilometers per second. In
1999, however, we discovered the unexpected phenomenon of
flows into the flare sites. Using the Soft
X-ray Telescope on the Yohkoh solar
observatory satellite, we detected features moving
downward into the tops of post-eruption arcade at
speeds of a few hundred kilometers per second. (See
the publication by McKenzie & Hudson,
1999; and also the press
release.)
We now believe that these flows represent the
retraction of magnetic flux tubes, shrinking to
relax magnetic tension after reconnection. My PhD student
Sabrina
Savage used Yohkoh, TRACE, and Hinode telescopes to
make quantitative measurements of
Supra-Arcade Downflows, in order to determine
the observational characteristics of magnetic
reconnection in flares. These observations formed the basis
of Sabrina's dissertation.
Some of my current research is focused on the magnetic arcades
(i.e., "rows of arches") which are often observed in the
corona following the eruption of a prominence/filament. In
addition to being quite beautiful, their structures and the
characteristics of their evolutions tell us about the
conditions of their environments, the magnetic fields that
define them, and the reconnection processes which create them.
An interesting subset of the flare arcades are the "spiky"
arcades, so called because of the tall, bright rays which
extend upward from their tops. In this movie (large: 5.5 MByte), you can see one of
these events, in which a fan of bright rays is formed on top
of the post-eruption arcade. (If you don't have the time to
download the full movie, try this still image
of a spiky post-eruption arcade.) Now ask yourself: How
does the Sun construct these exceedingly long, nearly linear
structures of 10-million-degree plasma? If they're magnetic,
which magnetic polarity is at the base of the spikes?
In solar physics, we are now convinced that magnetic
fields are rearranged, and magnetic energy is released, via a
set of processes which we refer to as magnetic
reconnection. However, we're lacking some specifics: How
fast does reconnection occur? How much flux is included in a
given reconnection event? What triggers an event? By
combining observational measurements with analytical estimates
and computer modeling, we hope to continue finding answers
to some of these questions.
A handful of links for checking on current solar
activity. Each of these will open in a new browser window,
since they are outside of the MSU site.
Back to McKenzie's
home page
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to Solar Physics group
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