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December 14: Valentine’s Day X-Flares: The First X-flares Seen by SWAP

  December 14: Valentine’s Day X-Flares: The First X-flares Seen by SWAP  
  Valentine’s Day X-Flares, first X-flares seen by SWAP  


Click on the above image for a link to a movie showing the flare



On Valentines day, Februrary 14th 2011, the Sun gave solar physicists something to smile about when it produced a series of flares from an active region near the center of the disk. One of these flares was the first X-class flare of Solar Cycle 24 and the first observed since December 2006, indicating increased solar activity in the current solar cycle. For the PROBA2 team, the X-flare was particularly significant because it was the first X-class flare observed with the SWAP EUV imager!

As discussed on day 7 and day 9 of the holiday countdown calendar, solar flares are seen as sudden brightenings on the Sun, created by the release of magnetic energy, with a single flare releasing as much as 6 × 1025 joules (over 10,000 times the world annual energy consumption!) over a wide spectrum of energies from radio waves to gamma rays. Solar flares are classified according to their brightness in x-ray wavelengths. Due to historical reasons they are classified as A, B, C, M or X according to their peak flux, where X-class flares are big; they are major events which can produce long-lasting radiation storms in Earth's upper atmosphere. M-class flares are medium-sized events and C-class flares are small with few noticeable consequences here on Earth. The number of flares seen on any given day varies, from several per day when the Sun is particularly "active" to less than one per week when the Sun is considered "quiet". Large flares are also less frequent than smaller ones. Go here for a brief discussion on flares.

The Sun has an activity cycle that lasts about 11 years, known as the solar cycle (or solar magnetic activity cycle). Each cycle begins and ends at solar minimum, when the Sun is relatively quiet. As we progress towards maximum in the middle of the cycle, there is an increase in the number of sunspots seen in the photosphere. As the number of sunspots grows, the magnetic field in the corona becomes more complicated meaning that we also see more flares, solar eruptions, and other visible manifestations indicating higher activity.

Solar Cycle 24 is the current and 24th solar cycle since records began in 1755. The cycle began in January  2008 during an extended minimum time, and there was little activity until early 2010. Although some M-class flares had been observed earlier in the cycle, the Februrary 14th 2011 X-class flare marked the first sign of significant activity in the current cycle. The flare peaked at 01:56 UT on February 15, 2011, and was related to sunspot group 1158. The flare had an associated Earth directed coronal mass ejection (CME). The CME impacted the Earth's magnetosphere on February 18 and triggered a minor G1-level geomagnetic storm.