Solar Flare, CME and Tsunami Generated by a “Blank Sun”

The empty solar disk on April 27th - still generated an X-ray flare (SOHO)

Even during solar minimum, the Sun can be surprisingly dynamic. We are currently observing a sunspot-less solar disk, but on Saturday the Solar and Heliospheric Observatory (SOHO) observed a noteworthy X-ray flare. It was a B3.8 flare, producing a coronal mass ejection (CME), sending vast quantities of hot plasma into interplanetary space. Admittedly, it is strange to witness CMEs of this size at this time in the solar cycle, but what is even weirder is that the flare was produced by a region devoid of sunspot activity (see image). SOHO captured the CME event with its LASCO instrument and the two-probe Solar Terrestrial Relations Observatory (STEREO) captured an incredible “solar tsunami” (or Sun Quake) as the flare caused the Sun’s surface to ripple. And all this without an intense magnetic field and sunspot pair…

Flares and sunspots go together like bread and butter; you very rarely find one without the other. Sunspots are manifestations of intense magnetic field lines being forced through the surface of the Sun, pushing the hot surface aside, exposing the cooler (and darker) solar interior. Projecting from these dark features one can expect arcades of coronal loops, plasma brightly radiating in EUV, and if they are hot enough, X-rays. Should the conditions be correct, magnetic reconnection may occur, unleashing huge quantities of stored magnetic energy.

Although magnetic field lines were present at the site of the April 26th flare, there didn’t appear to be much going on, and certainly no signs of a sunspot. Then at 1408 UT a huge flare was ignited and a large CME followed. At the same time, STEREO (a pair of solar observatories viewing the Sun at different locations) saw immense ripples speed over the solar surface.

Animation of the CME event. Observation by SOHOs LASCO C3 instrument (SOHO)

Generally speaking, the strong magnetic field required to generate such a large event should leave it’s footprints as sunspots, but having an X-ray flare without sunspots will be sure to excite solar physicists for a long time. Where did the energy for this flare and CME come from? What triggered it? Why were there no sunspots at that location? Why is the Sun so active when it is predicted to be at a low-energy state? I will be looking into these questions and taking an educated guess over the coming days. So stay tuned!

Thanks to Susan Martin at the Mars Foundation for bringing my attention to this news!

Source: Space Weather

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