HOLE IN THE SUN’S ATMOSPHERE: A vast hole has opened in the atmosphere over the sun’s south pole, and it is spewing solar wind into space. The gaseous gap, a.k.a. a ‘coronal hole,’ is colored dark-purple in this extreme ultraviolet image from NASA’s Solar Dynamics Observatory:
Curved lines trace the sun’s magnetic field in this EUV image from SDO
Coronal holes are places where the sun’s magnetic field opens up and allows solar wind to escape. A stream of solar wind flowing from this particular hole is expected to reach Earth’s orbit on Jan. 4-5. The bulk of the stream will flow south of our planet. However, not all of it will miss. NOAA forecasters estimate a 40% chance of polar geomagnetic storms when the solar wind arrives in the next 48 hours.
CME TARGETS EARTH, AFTER ALL: On Nov. 7th, when an X-flare from AR2205 hurled a CME into space, at first it appeared that the cloud would miss Earth. Follow-up computer modeling by NOAA analysts suggests that the CME might deliver a glancing blow to our planet’s magnetic field after all. A complete forecast follows this movie of the eruption recorded by the Solar and Heliospheric Observatory:
The CME left the sun traveling approximately 600 km/s (1.3 million mph) albeit not directly along the sun-Earth line. If the computer models are correct, the outskirts of the cloud should reach Earth mid-day on Nov. 10th (Universal Time). First contact could spark a G2-class geomagnetic storm on Nov. 10th subsiding to G1-class on Nov. 11th. NOAA forecasters are citing storm probabilities as high as 75%.
These storms in the forecast are mild, not extreme, so there is no danger of power outages or communications blackouts. However, the CME impact could spark some beautiful auroras around the Arctic Circle. The lights might even spill across the Canadian border into northern-tier US states such as Maine, Michigan, Minnesota and the Dakotas.
STORM WARNING (UPDATED): Among space weather forecasters, confidence is building that Earth’s magnetic field will receive a double-blow from a pair of CMEs on Sept. 12th. The two storm clouds were propelled in our direction by explosions in the magnetic canopy of sunspot AR2158 on Sept. 9th and 10th, respectively. Strong geomagnetic storms are possible on Sept. 12th and 13th as a result of the consecutive impacts. Sky watchers, even those at mid-latitudes, should be alert for auroras in the nights ahead. Aurora alerts:text, voice
EARTH-DIRECTED X-FLARE AND CME: Sunspot AR2158 erupted on Sept. 10th at 17:46 UT, producing an X1.6-class solar flare. A flash of ultraviolet radiation from the explosion (movie) ionized the upper layers of Earth’s atmosphere, disturbing HF radio communications for more than an hour. More importantly, the explosion hurled a CME directly toward Earth. The Solar and Heliospheric Observatory photographed the expanding cloud:
Updated: Radio emissions from shock waves at the leading edge of the CME indicate that the cloud tore through the sun’s atmosphere at speeds as high as 3,750 km/s. By the time it left the sun’s atmosphere, however, the cloud had decellerated to 1,400 km/s. This makes it a fairly typical CME instead of a “super CME” as the higher speed might suggest.
Even with a downgrade in speed, this CME has the potential to trigger significant geomagnetic activity when it reaches Earth’s magnetic field during the mid-to-late hours of Sept. 12th. NOAA forecasters estimate an almost-80% chance of polar geomagnetic storms on Sept. 12-13.
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.
