A Fat Filament and a Phoenix
Science Nugget: October 15, 1999 -
`I'm worried about that filament; it's gonna go and we're gonna miss the
flare'; paraphrasing Joe Khan, resident Yohkoh/BCS expert. He was correct
about the first part; the filament did 'go', and this constitutes one of
the rare times that a solar physicist makes a worthwhile prediction. But
he was wrong about the second part, since as far as we can tell there was
no flare... However Yohkoh SXT did see the formation of a splendid arcade,
which most certainly wins the weekly aesthetics trophy.
Clicking below will play a movie of this event, generated from SXT full-disk
images. Note the faint arch present before the eruption and the small jet
which may or may not have something to do with the eruption onset. Fine,
wispy loops are visible at the southern end of the arcade.
Why the statement?
Joe had been watching the evolution of a quiescent H alpha filament, near
the solar north pole, over a couple of days, and the thickening and darkening
of said filament made him suspect that it was not long for this world (see
Science Nuggets for Week
21 1998 for more about filaments in general, and for Week
25 1999 for another gorgeous SXT-observed polar crown eruption).
Below are a series of Kitt Peak He 10830 images showing the development
and disappearance of the fat filament, in the north.
09-Oct-99 17:39 UT
12-Oct-99 18:22 UT
It is `well known' that prior to eruption, a filament becomes darker
and breaks up, as these images show. There was a fair chance that this
filament would erupt. In the last of the SXT images below, the bright
arcade shows that this did indeed happen. Triumph!
09-Oct-99 11:38 UT
12-Oct-99 12:20 UT
13-Oct-99 12:34 UT
What's going on?
Like the filament eruption presented in Science
nugget 1999/w25, the filament eruption followed by arcade formation
are an observationally well-established pattern. The mechanism whereby
filament eruption happens is still hotly debated, however it
is generally accepted that after the filament lifts off, the field reconnects,
or reconfigures, behind it. This results in the hot arcade of loops observed
by Yohkoh SXT.
And the Phoenix...?
13-Oct-99 12:42 UT
....coined when we looked at the LASCO
C2 image of the event (left). LASCO C2 shows an expanding bubble, launched
at around 10:00 UT, with twisted internal structure (the phoenix).
At 12:26 UT the leading edge of the bubble extends to about 6 solar radii.
LASCO C3 also shows this bubble of field and plasma moving away from the
sun. Spectacular movies of this event can be found by clicking
(C2) and here
(C3). Warning -- these are big MPEG files (884K and 572K respectively),
and may take a while to download.
Lyndsay Fletcher <email@example.com>
October 15, 1999