A beautifully observed major flare

Science Nugget: April 13, 2001

Timely arrival

Today, just three hours ago, yet another major "geoeffective" flare took place. For this event our instruments on board Yohkoh were poised and ready, and Yohkoh was flying through clear sunshine at the time of the flare. Readers of these Web pages will know that this is not always the case! So here is a hurry-up view of this event, even as its "solar cosmic rays" arrive at the Earth and disturbances of the Earth's environment continue. Here's a preface view:

Which just shows the Sun in two ways right before the flare popped off. The time of this image was 10:11:18 UT, April 12, 2001. On the left, our usual logarithmic compression, which shows faint things well; on the right, a true linear representation, whereby one can see that only the region about to flare is visible at all! Such is the enormous contrast range of the solar corona. This can be put into a proper time scale by reference to our usual time-series plot.

Ejecta and restructuring

We caught the very beginning of this event, because the preflare active region was so bright that Yohkoh's attention was already properly focused. Thus we see below a rare continuous movie of the actual flare onset (click here for a version that will download much more quickly):

Again we have made a time-series plot, showing the image times for the movie in the context of the hard X-ray emission. The vertical lines in this plot get denser in time when flare mode begins (more telemetry, more image).

The movie shows a general outward motion of what appear to be nested loops. The appearance of discontinuous motion - a sudden jump - is deceptive, because the movie frames are not uniformly distributed in time. So be careful!

Here's the ejection on a larger scale (5 arc min FOV, still showing a tiny region by the standards of a coronagraph observation, but the seed of an enormous coronal disruption):

Perhaps the striking thing here is the homologous appearance of the erupting loops and the ones choosing, for obscure reasons, not to erupt this time. Of course ignore the bright upward spikes, they are image saturation.

Incongruous note

This flare certainly produced a Type II burst, as J. Khan confirmed by taking a peek at the Potsdam spectrograph data. There will be good observations from many European observatories. The incongruous note here is that we had just been about to commence a new and better observational scheme, at Khan's request, for global waves (see our first hints at this possibility in a science nugget from two years ago. But we couldn't upload the new commands because this flare was in progress! So, we'll have to wait til next time to see how this plays out.

Note on restructuring

It's becoming clearer and clearer that the geometrical re-formation of the coronal magnetic field plays a decisive role in all kinds of phenomena. This flare exhibited a small peculiarity in this regard. Early on, the axis of symmetry tilted towards higher latitudes; later on, towards lower latitudes:

Perhaps, seen this near the limb (lines shown in the plots above), this is a manifestation of twist. We know that this is an important ingredient for these beautiful events...

Note: We now maintain a topic index of the Yohkoh science nuggets.

April 13, 2001

Hugh Hudson <hudson@lmsal.com>.