Powerful Solar Flare Causes Radio Blackout
The solar flare as observed by NASA's Solar Dynamics Observatory in extreme ultraviolet light.
The sun may be an average star when compared to the menagerie of stars that exist in our galaxy, but to Earth and all life on our planet, the sun is the most important object in the Universe. However, regardless of its importance and close proximity, our nearest star holds many mysteries that continue to fox solar physicists after decades of modern studies with cutting-edge observatories. One of the biggest mysteries surrounding the sun is the underlying mechanisms that drive solar flares and coronal mass ejections (CMEs). Monday evening (EST), the sun reminded us that it hasn't quite finished with the current solar maximum (of solar cycle 24), unleashing a powerful X4.9 solar flare -- the biggest of 2014. An armada of space telescopes witnessed the event, including NASA's Solar Dynamics Observatory that can spy the sun's temper tantrums in astounding high definition. Shown here, 5 of the 10 filters from the SDO's Atmospheric Imaging Assembly (AIA) instrument are featured, showing the sun's lower corona (the solar multimillion degree atmosphere) through 5 wavelengths; each wavelength of extreme ultraviolet light representing a different plasma temperature and key coronal features -- such as coronal loops (highlighted here in the 'yellow' 171A filter) and ejected plasma that formed a CME.
At 7:13 p.m. EST (00:13 UT, Feb. 25) -- pictured here on the far left -- the active region (AR) 1990 was crackling with activity. Then, as magnetic field lines from the sun's interior forced together and through the solar photosphere, large-scale reconnection events occurred. Reconnection is a magnetic phenomena where field lines "snap" and reconnect, releasing huge quantities of energy in the process. At 7:44 p.m. EST (00:44 UT) -- second frame from the right -- a kinked coronal loop can be seen rising into the corona. At 7:59 p.m. EST (00:59 UT) -- far right -- solar plasma contained within the magnetic flux is accelerated to high energy, generating powerful x-rays and extreme ultraviolet radiation, creating the X-class flare.
The X4.9 flare was caught through the range of SDO fliters, including this dramatic view as seen through the 131A filter. The flare was so bright that photons from the flare overloaded the SDO's CCD inside the AIA instrument, causing the signal to "bleed" across the pixels. This bleeding effect is common for any optical instrument observing powerful solar flares.
Intense coronal activity is often associated with active regions -- the active lower corona is pictured here, left. In this case, the flare erupted from AR1990, at the limb of the sun. Also associated with active regions are sunspots, dark patches observed in the sun's photosphere (colloquially known as the sun's "surface") -- pictured right. The sun's cooler photosphere has been imaged by a different SDO instrument called Helioseismic and Magnetic Imager (HMI), which detects the intensity of magnetic fields threading though the sun's lower corona and photosphere.
In the case of AR1990, a large sunspot can be seen at the base of the coronal loops that erupted to generate the powerful flare. This is a prime example of how sunspots can be used to gauge solar activity and how they are often found at the base of intense coronal activity and flares.
The HMI monitors magnetic activity across the disk of the sun and can also generate a picture on the direction of the magnetic field polarity. In this observation of the sun's magnetic field around the time of the recent X-class flare, other active regions can be easily seen -- intense white and black regions highlighting where magnetic field lines emerge and sink back into the sun's interior in active regions.
The joint NASA/ESA Solar and Heliospheric Observatory (SOHO), which has been watching the sun since 1996, also spotted the flare, tracking a CME that was generated shortly after. Seen here by SOHO's LASCO C2 instrument, that monitors the interplanetary environment surrounding the sun for CMEs and comets, a growing bubble of solar plasma races away from the sun.
Approximately an hour after the flare, the CME grew and continued to barrel into interplanetary space. Space weather forecasters don't expect that this CME will interact with the Earth's atmosphere as it is not Earth-directed. This observation was captured by SOHO's LASCO C3 instrument -- an occulting disk covers the sun to block out any glaring effect. By combining observations by the SDO, SOHO and other solar observatories, the connection between the sun's internal magnetic "dynamo", the solar cycle, flares and CMEs, solar physicists are slowly piecing together what makes our nearest star tick, hopefully solving some of the most persistent mysteries along the way.
On Saturday, the sun erupted with an X-class solar flare, blasting Earth with powerful electromagnetic radiation. Although we couldn’t directly feel its effects on the ground, the impact of this event was measured as a dramatic radio blackout for several minutes, highlighting the fact that the sun isn’t quite done with solar maximum yet.
The X1.0 flare erupted at 1:48 p.m. ET on March 29 and an armada of solar telescopes captured the event in all its glory. A solar flare occurs when highly-stressed magnetic field lines are forced together over regions of intense magnetic activity, descriptively known as “active regions.” These regions are often associated with sunspot clusters — this is why astronomers keep count of sunspots in an effort to record solar activity.
Although we are well protected from the worst effects of radiation from solar flares, ionizing X-ray and extreme ultraviolet radiation can have a disruptive impact on unshielded satellite electronics and can even give unprotected astronauts an increased radiation dose. Our atmosphere is a thick shield that protects our biology from the sun’s worst solar flares, but that’s not to say that they can’t impact our lives.
As reported by Spaceweather.com, the X1 flare, which was triggered above active region (AR) 2017, bathed our upper atmosphere in ultraviolet radiation, causing global ionization. The aptly-named ionosphere is used for communications where radio waves are bounced around the globe. This extensive ionization event caused the propagation of radio waves to wildly fluctuate, eventually blocking them all together. The blast was so powerful that the impulsive electrical currents generated in the ionosphere caused vast waves to ripple through our planet’s magnetic field.
Radio engineer Stan Nelson located in Roswell, New Mexico, was monitoring the National Institute of Standards and Technology (NIST) WWV radio transmission (which transmits time and frequency information worldwide 24/7) during the flare and watched the signal oscillate wildly before being blocked all together.
“The Doppler shift of the WWV signal (the ‘wobble’ just before the blackout) was nearly 12 Hz, the most I have ever seen,” said Nelson.
The flare also generated its own radio signal; as the flare’s shock wave blasted through the sun’s corona (its atmosphere), an intense radio signal was generated and was recorded as powerful shortwave radio static.
The sun is currently experiencing the wane of solar maximum, the peak of its approximate 11-year solar cycle. Solar Cycle 24 has been a “below average” cycle exhibiting lower levels of magnetic activity — but as Saturday’s flare proves, it’s still capable of generating some impressive explosive displays.