A Fat Filament and a Phoenix

Science Nugget: October 15, 1999 -

The statement:

`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              13-Oct-99 17:24UT

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 12:26 UT                         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 here (C2) and here (C3). Warning -- these are big MPEG files (884K and 572K respectively), and may take a while to download.

Lyndsay Fletcher <fletcher@sag.lmsal.com>
October 15, 1999