From Eos: “Largest Flare of Past 9 Years Erupts from Sun”

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9.8.17
Kimberly M. S. Cartier

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NASA’s Solar Dynamics Observatory captured this image, blended from two ultraviolet filters, of (left) the X9.3 class solar flare that erupted from the Sun on 6 September and (right) a simultaneous smaller flare from a different active region. Credit: NASA/Goddard Space Flight Center/Solar Dynamics Observatory

NASA/SDO

A flare erupting from the surface of the Sun on Wednesday blocked communications and interfered with navigational frequencies across the globe. Large portions Europe, Africa, Asia, and Australia experienced disruptions to low-frequency radio communications, according to the U.S. National Oceanic and Atmospheric Administration (NOAA).

As the flare jetted outward from the Sun’s surface, the star’s outer atmosphere, or corona, belched a huge cloud of ultrahot, electrically charged particles, known as a coronal mass ejection (CME) toward Earth. The CME prompted a warning from NOAA solar storm watchers of an impending strong (G3) geomagnetic storm or greater through today. An updated NOAA report at 1:57 p.m. Coordinated Universal Time (UTC) today revised the agency’s assessment to “G4 (Severe) geomagnetic storm levels” for the day-lit side of Earth.

In addition to roiling communications and navigation signals, such geomagnetic storms can create surges or shutdowns in power grids and produce brilliant auroras visible at lower latitudes than usual.

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Two solar flares exploded from the same region of the Sun within a few hours of each other. This time-lapse footage of the region, seen here in extreme-ultraviolet wavelengths, shows flares and CMEs many times larger than Earth. Credit: NASA/Goddard Space Flight Center/SDO

According to NOAA’s Space Weather Prediction Center, the flare sprung from the Sun at 12:02 p.m. UTC on 6 September, accompanied by the CME, which arrived at Earth late last night and is expected to persist through today.

A Blast amid the Calm

NOAA heliophysicists identified Wednesday’s flare as the largest solar flare to date in the current solar cycle, which is an approximately 11-year cycle that tracks when solar activity increases and decreases. The current solar cycle began in December 2011. Although the Sun’s activity is declining on average, large flares such as these are not uncommon during this stage of the cycle.

“Some of the strongest solar events occur near solar minimum,” Thomas Zurbuchen, associate administrator of NASA’s Science Mission Directorate, explained on Twitter. “Space Weather matters during the entire solar cycle!”

Heliophysicists associated with NASA’s Solar Dynamics Observatory (SDO) classified this event as an X9.3 solar flare, meaning it’s in the most intense class of flares. What’s more, the same region of the Sun had produced another X-class flare about 3 hours earlier on the morning of 6 September. Three other moderate-intensity flares have exploded from the region since 4 September, in addition to flares from other active areas on the Sun’s surface.

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The Sun produced five strong solar flares from 4 to 7 September, including the X9.3 event that generated the large CME near time mark “2017/09/06 14:00.” CMEs are best observed when the bright disk of the Sun is blocked by a coronagraph, as seen in this sequence of images taken by the Large Angle and Spectrometric Coronagraph (LASCO) instrument on the NASA/ESA Solar and Heliospheric Observatory (SOHO). Credit: SOHO/LASCO/National Research Laboratory team

“It’s the active region that keeps on giving!” tweeted Sophie Murray, a space weather scientist at Trinity College in Dublin, Ireland.

NOAA’s Space Weather Prediction Center also reported a strong (R3) radio blackout on Wednesday at 9:10 a.m. UTC due to both flares that day.

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