ALMOST-X FLARE: Departing sunspot AR1996 erupted on March 12th at 2234 UT, producing an M9-category blast that almost crossed into X-territory. NASA’s Solar Dynamics Observatory captured the extreme ultra-violet flash:
UV radiation from the flare caused waves of ionization to ripple through Earth’s upper atmosphere. These waves briefly altered the propagation of low-frequency radio transmisions around the planet, as shown in this plot from amateur radio astronomer Jim Tegerdine of Marysville, Washington. Otherwise the flare was not geoeffective. The sunspot’s location near the sun’s eastern limb mitigated Earth effects.
The next big flare could have a greater influence on our planet. Sunspot AR2002 is directly facing Earth, and it has a ‘beta-gamma-delta’ magnetic field that harbors energy for strong explosions. NOAA forecasters estimate an 80% chance of M-class flares and a 15% chance of X-flares on March 13th
RADIOACTIVE’ ERUPTION: On Feb. 17th at approximately 04:50 UT, a magnetic filament erupted from the sun’s western limb. NASA’s Solar Dynamics Observatory captured this high-resolution image of the blast:
Because of its location on the sun’s western limb, the eruption did not send a CME toward Earth. However, there was an effect on our planet: Shortwave radio loudspeakers roared with static, an event called a Type II radio burst.
Here’s how it works: The explosion sent shock waves rippling through the sun’s atmosphere. Those shock waves, in turn, triggered plasma instabilities in the solar corona that emit strong radio emissions. The static-y “roar” of the explosion was picked up by solar observatories and ham radio stations across the dayside of our planet. Based on the sweep of radio frequencies from 20 MHz to 500 MHz, analysts estimate a shock velocity of 776 km/s or 1.7 million mph. That may sound fast, but it is typical for this type of eruption.
X-CLASS SOLAR FLARE: Sprawling suunspot AR1897 erupted on Nov. 19th (10:26 UT), producing an X1-class solar flare. NASA’s Solar Dynamics Observatory recorded the explosion’s extreme ultraviolet flash:
Although the sunspot is not directly facing Earth, the flare did affect our planet. Mainly, the UV flash produced a wave of ionization in the upper atmosphere over Europe, Africa and parts of Asia. A brief blackout of HF radio transmissions around the poles might have also occurred. First-look coronagraph data from NASA’s STEREO-Ahead probe show a CME emerging from the blast site, but it is probably not heading for Earth.
SOLAR FLARE CAUSES RARE ‘MAGNETIC CROCHET’: On Nov. 5th at 22:12 UT, the magnetic canopy of sunspot AR1890 erupted, producing a brief but intense X3-class solar flare. NASA’s Solar Dynamics Observatory recorded the extreme ultraviolet flash:
Radiation from the flare caused a surge in the ionization of Earth’s upper atmosphere–and this led to a rare magnetic crochet. Alexander Avtanski observed the effect using a homemade magnetometer in San Jose, California. A magnetic crochet is a disturbance in Earth’s magnetic field caused by electrical currents flowing in air 60 km to 100 km above our heads. Unlike geomagnetic disturbances that arrive with CMEs days after a flare, a magnetic crochet occurs while the flare is in progress. They tend to occur during fast impulsive flares like this one.
More eruptions are in the offing. NOAA forecasters estimate a 45% chance of M-class solar flares and a 10% chance of X-flares on Nov. 7th.
X2-FLARE BLASTS EARTH’S IONOSPHERE: Electromagnetic radiation from the X2-class solar flare of Oct. 25th had a significant effect on Earth’s upper atmosphere. As a wave of ionization swept across the dayside of the planet, the normal propagation of shortwave radio signals was scrambled. In Alachua, Florida, electrical engineer Wes Greenman recorded the effects using his own shortwave radio telescope. Click on the frequency-time plot to view an animation:
During the time that terrestrial shortwave transmissions were blacked out, the sun filled in the gap with a loud radio burst of its own. In New Mexico, amateur radio astronomer Thomas Ashcraft recorded the sounds. “This radio burst was a strong one and might be too intense for headphones,” cautions Ashcraft.
Solar radio bursts are caused by strong shock waves moving through the sun’s atmosphere. (Electrons accelerated by the shock front excite plasma instabilities which, in turn, produce shortwave static.) They are usually a sign that a CME is emerging from the blast site–and indeed this flare produced a very bright CME.
INTERCONNECTED SOLAR ACTIVITY: The X1-flare of Oct. 25th was remarkable not only for its strength, but also for its interconnectedness. The flare was bracketed by two erupting magnetic filaments, each located hundreds of thousands of kilometers from the instigating sunspot AR1882. The whole episoide, shown in this SDO movie, was reminiscent of the famous global eruption of August 2010.
Today, Oct. 26th, it happened again. Click on this image of the sun’s southwestern quadrant and watch a sequence of flare activity around sunspots AR1875 and AR1877 followed by a filament eruption off the SW limb:
Instead of being a sequence of unrelated events, these flares and eruptions are likely connected by magnetic fields, which thread through the whole broad region. Like dominoes falling, one explosion triggers another as shock waves follow magnetic fields from blast site to blast site.
The filament punctuated the sequence by hurling a part of itself into space. SOHO has observed a CME emerging from the blast site, but it is too soon to say whether it is heading for Earth.
SOLAR FLARE! Solar activity is high. On October 24th at 00:30 UT, Earth-facing sunspot AR1877 erupted, producing a powerful M9-class solar flare. NASA’s Solar Dynamics Observatory recorded the blast:
Update #1: The eruption hurled a faint CME into space and it appears to be heading toward Earth. The arrival time is not yet known.
Update #2: NASA’s Solar Dynamics Observatory has released a full-disk movie of the explosion. Play it.
More flares are in the offing. Two large sunspots, AR1875 and AR1877, have ‘beta-gamma-delta’ magnetic fields that harbor energy for strong eruptions. NOAA forecasters estimate a 40% chance of M-flares and a 5% chance of X-flares during the next 24 hours.
FARSIDE ERUPTION: An active region located just behind the sun’s northeastern limb erupted this morning, producing an X-ray flash that registered M1.5 on the Richter Scale of Solar Flares — despite the fact that it was partially eclipsed by the edge of the sun. The true intensity of the flare was much greater, possibly X-class. The explosion also hurled a spectacular CME into space:
Type II radio emissions from the expanding cloud suggest an expansion velocity of at least 510 km/s (1.1 million mph). That’s a typical speed for CMEs.
Within a few days, the sunspot responsible for this outburst will rotate around to the Earthside of the sun. At that time, Earth-directed solar activity could increase. August and September were quiet months, but in October the sun seems to be waking up
CORONAL HOLE: NASA’s Solar Dynamics Observatory is monitoring a coronal hole in the sun’s northern hemisphere. It is the UV-dark region in this image taken during the early hours of Sept. 21st:
The white lines in the image trace the sun’s magnetic field. A coronal hole is a place where the magnetic field spreads apart, allowing solar wind to escape. A stream of solar wind flowing from this particular coronal hole is heading for Earth, due to arrive on Sept. 23-24. Its arrival could add to the impact of a minor CME expected to reach Earth at about the same time. Polar geomagnetic storms are possible early next week.
SUNDIVING COMET AND FULL-HALO CME: A small comet plunged into the sun this morning, and just before it arrived, the sun expelled a magnificent full-halo CME. Click to view a movie from the Solar and Heliospheric Observatory (SOHO):
In the final frames of the movie, the comet can be seen furiously vaporizing. Indeed, those were the comet’s final frames. It did not emerge again from its flyby of the hot sun. “With a diameter of perhaps a few tens of meters, this comet was clearly far too small to survive the intense bombardment of solar radiation,” comments Karl Battams of the Naval Research Lab, who studies sungrazing comets.
The CME (coronal mass ejection) came from an explosion on the farside of the sun. Although the CME and the comet appear to intersect, there was probably no interaction between the two. The comet is in the foreground and the farside CME is behind it.
Occasionally, readers ask if sundiving comets can trigger solar explosions. There’s no known mechanism for comets to spark solar flares. Comets are thought to be too small and fragile to destabilize the sun’s magnetic field. Plus, this comet was still millions of kilometers from the sun when the explosion unfolded.
The comet, R.I.P., was a member of the Kreutz family. Kreutz sungrazers are fragments from the breakup of a single giant comet many centuries ago. They get their name from 19th century German astronomer Heinrich Kreutz, who studied them in detail. Several Kreutz fragments pass by the sun and disintegrate every day. Most, measuring less than a few meters across, are too small to see, but occasionally a bigger fragment like this one attracts attention.