Instruct: Given a question, retrieve relevant passages that can help answer the question.
Query: How often do solar flares occur?
The frequency of occurrence of solar flares varies, from several per day when the Sun is particularly "active" to less than one every week when the Sun is "quiet", following the 11-year cycle (the solar cycle). Large flares are less frequent than smaller ones.
Coronal mass ejections often appear with other forms of solar activity, most notably solar flares, but no causal relationship has been established. Most weak flares do not have CMEs; most powerful ones do. Most ejections originate from active regions on the Sun's surface, such as sunspot groupings associated with frequent flares. Other forms of solar activity frequently associcated with coronal mass ejections are eruptive prominences, coronal dimming, coronal waves and Moreton waves, also called solar tsunami.
A coronal cloud is released when a solar flare becomes a coronal mass ejection; the coronal cloud often contains more radioactive particles than the mass ejection itself. A coronal mass ejection occurs when a solar flare becomes so hot that it snaps and breaks in two, becoming a "rope" of heat and magnetism that stretches between two sunspots. The resulting coronal mass ejection can be compared to a horseshoe magnet, the sunspots being the poles and the oscillating magnetic connector the handle. Coronal mass ejections typically do not last very long, because they cool down as the coronal cloud of gas is released and begins to hurtle away from the sun.
The Bastille Day Flare or Bastille Day Event was a powerful solar flare on July 14, 2000, the national day of France, occurring near the peak of the solar maximum in solar cycle 23. The X5.7-class flare originated from a sunspot known as Active region 9077, which subsequently caused an S3 radiation storm on Earth fifteen minutes later as energetic protons bombarded the ionosphere. It was the biggest solar radiation event since 1989. The proton event was four times more intense than any previously recorded since the launches of SOHO in 1995 and ACE in 1997. The flare was also followed by a full-halo coronal mass ejection and a geomagnetic super storm on July 15–16. The geomagnetic storm peaked at the extreme level, G5, in the late hours of July 15.
Since superflares can occur on stars apparently equivalent in every way to the Sun, it is natural to ask if they can occur on the Sun itself. An estimate based on the original Kepler photometric studies suggested a frequency on solar-type stars (early G-type and rotation period more than 10 days) of once every 800 years for an energy of 10 erg and every 5000 years at 10 erg. One-minute sampling provided statistics for less energetic flares and gave a frequency of one flare of energy 10 erg every 5–600 years for a star rotating as slowly as the Sun; this would be rated as X100 on the solar flare scale. This is based on a straightforward comparison of the number of stars studied with the number of flares observed. An extrapolation of the empirical statistics for solar flares to an energy of 10 erg suggests a frequency of one in 10,000 years.
Solar flares occur in a power-law spectrum of magnitudes; an energy release of typically 1020 joules of energy suffices to produce a clearly observable event, while a major event can emit up to 1025 joules.[2]
Four solar flares occurred within 5 days from sunspot AR 12192, which is both the largest sunspot of solar cycle 24 and the largest since 1990. On October 19 there was a major X1.1-class solar flare. October 22 an M8.7-class flare was followed the same day by an X1.6 event. The October 24 X3.1-class solar flare was strong enough to trigger a radio blackout. Larger than the planet Jupiter, the AR 12192 sunspot was visible during a partial solar eclipse seen in North America.
A prominence eruption producing a CME shot off the east limb (left side) of the Sun on April 16, 2012. Such eruptions are often associated with solar flares, and in this case an M1.7 class (medium-sized) flare occurred at the same time, peaking at 1:45 PM EDT and 17.45 UTC. The CME was not aimed toward Earth. Nevertheless, this month was very quiet in comparison to the previous one, as only two M-class flares were recorded.
Flares occur when accelerated charged particles, mainly electrons, interact with the plasma medium. Evidence suggests that the phenomenon of magnetic reconnection leads to this copious acceleration of charged particles.[7] On the Sun, magnetic reconnection may happen on solar arcades– a series of closely occurring loops following magnetic lines of force. These lines of force quickly reconnect into a lower arcade of loops leaving a helix of magnetic field unconnected to the rest of the arcade. The sudden release of energy in this reconnection is the origin of the particle acceleration. The unconnected magnetic helical field and the material that it contains may violently expand outwards forming a coronal mass ejection.[8] This also explains why solar flares typically erupt from active regions on the Sun where magnetic fields are much stronger.
Solar flares affect all layers of the solar atmosphere (photosphere, chromosphere, and corona). The plasma medium is heated to tens of millions of Kelvin, while electrons, protons, and heavier ions are accelerated to near the speed of light. Flares produce electromagnetic radiation across the electromagnetic spectrum at all wavelengths, from radio waves to gamma rays. Most of the energy is spread over frequencies outside the visual range and so the majority of the flares are not visible to the naked eye and must be observed with special instruments. Flares occur in active regions around sunspots, where intense magnetic fields penetrate the photosphere to link the corona to the solar interior. Flares are powered by the sudden (timescales of minutes to tens of minutes) release of magnetic energy stored in the corona. The same energy releases may produce coronal mass ejections (CMEs), although the relationship between CMEs and flares is still not well understood.
Other large solar flares also occurred on April 2, 2001 (X20),[36] October 28, 2003 (X17.2 and 10),[37] September 7, 2005 (X17),[36] February 17, 2011 (X2),[38][39][40] August 9, 2011 (X6.9),[41][42] March 7, 2012 (X5.4),[43][44] July 6, 2012 (X1.1).[45] On July 6, 2012, a solar storm hit just after midnight UK time,[46] when an X1.1 solar flare fired out of the AR1515 sunspot. Another X1.4 solar flare from AR 1520 region of the Sun,[47] second in the week, reached the Earth on July 15, 2012[48] with a geomagnetic storm of G1–G2 level.[49][50] A X1.8-class flare was recorded on October 24, 2012.[51] There has been major solar flare activity in early 2013, notably within a 48-hour period starting on May 12, 2013, a total of four X-class solar flares were emitted ranging from an X1.2 and upwards of an X3.2,[52] the latter of which was one of the largest year 2013 flares.[53][54] Departing sunspot complex AR2035-AR2046 erupted on April 25, 2014 at 0032 UT, producing a strong X1.3-class solar flare and an HF communications blackout on the day-side of Earth. NASA's Solar Dynamics Observatory recorded of extreme ultraviolet radiation from the explosion. The Solar Dynamics Observatory recorded an X9.3-class flare at around 1200 UTC on September 6, 2017.[55]
Solar storms of different types are caused by disturbances on the Sun, most often coronal clouds associated with coronal mass ejections (CMEs) produced by solar flares emanating from active sunspot regions, or, less often, from coronal holes. Solar filaments (solar prominences) may also trigger CMEs, trigger flares, or occur in conjunction with flares, and associated CMEs can be intensified.
As Hyder flares are notably rare, few occurrences have been recorded since their discovery, the first being on August 31, 2012, the second being on June 4, 2014. This solar flare occurred in the Southeastern Galactic quadrant. This flare spanned more than . It was recorded to have happened around 14:30 Coordinated Universal Time (UTC). After the flare took place, solar activity was low for 24 hours.
These are injections of energetic electrons, protons, alpha particles into interplanetary space during solar flare eruptions. During periods of maximum solar activity, the frequency and intensity of solar flares will increase. The solar proton events generally occur only once or twice a solar cycle.
A filament eruption occurred in late hours of September 27 resulted in a brief S1 (minor) radiation storm, alerted by NOAA in early hours of next day. The Earth-directed CME associated with this event affected our planet on September 30. Geomagnetic storm levels reached the G3 on October 1. The filament eruption was connected to a C3.7 flare occurred in the vicinity of sunspot 1577.
Solar activity decreased remarkably this month. 4 minor solar flares, below M2 levels, were registered in September 2012.
On October 8 and 9, the arrival of a CME unrelated to solar flares and emitted on October 5 caused disturbances in the horizontal component of the Earth's magnetic field. The planetary Kp-index reached level 6, so a G2 (moderate) geomagnetic storm was reported. 
The Sun released a M9.0 flare on October 20. This was followed three days after on October 23, by a very impulsive flare, peaking as an X1.8 class event at 3:17 a.m. UTC. 
Both flares came from active region 1598 located on the left side (east) of the sun, which had previously been the source of a number of weaker flares. The M9.0 burst occurred when the sunspot was not yet rotated onto the Earth-facing side of the solar disk. The NOAA categorized the radio blackout associated with the X1.8 event as an R3, on a scale from R1 to R5. This was the 7th and last X-class flare in 2012. There was no associated Earth-directed coronal mass ejection (CME).
Solar minimum is the period of least solar activity in the 11 year solar cycle of the Sun. During this time, sunspot and solar flare activity diminishes, and often does not occur for days at a time. The date of the minimum is described by a smoothed average over 12 months of sunspot activity, so identifying the date of the solar minimum usually can only happen 6 months after the minimum takes place. Solar minima are not generally correlated with changes in climate but recent studies have shown a correlation with regional weather patterns.
Coronal mass ejections are often associated with other forms of solar activity, most notably:
The association of a CME with some of those phenomena is common but not fully understood. For example, CMEs and flares are normally closely related, but there was confusion about this point caused by the events originating beyond the limb. For such events no flare could be detected. Most weak flares do not have associated CMEs; most powerful ones do. Some CMEs occur without any flare-like manifestation, but these are the weaker and slower ones. It is now thought that CMEs and associated flares are caused by a common event (the CME peak acceleration and the flare impulsive phase generally coincide). In general, all of these events (including the CME) are thought to be the result of a large-scale restructuring of the magnetic field; the presence or absence of a CME during one of these restructures would reflect the coronal environment of the process (i.e., can the eruption be confined by overlying magnetic structure, or will it simply break through and enter the solar wind).
"Sunquakes" caused by solar flares were first observed during this cycle. These are running acoustic waves, as opposed to the standing waves that constitute the material of helioseismology. The flare impulse launches these waves from the photosphere, and they arc deeply into the interior of the Sun before refracting back to the surface to appear as faint ripples, expanding radially away from the flare some tens of minutes later. The flare in which these waves were first observed, SOL1996-07-09, occurred more than three years after the last previous major event.
Magnetic reconnection occurs during solar flares, coronal mass ejections, and many other events in the solar atmosphere. The observational evidence for solar flares includes observations of inflows/outflows, downflowing loops, and changes in the magnetic topology. In the past, observations of the solar atmosphere were done using remote imaging; consequently, the magnetic fields were inferred or extrapolated rather than observed directly. However, the first direct observations of solar magnetic reconnection were gathered in 2012 (and released in 2013) by the High Resolution Coronal Imager.
"Flare" describes the world as it may be in 2081, and the effects a future inter-planetary civilization would suffer if a solar flare occurred after almost 100 years without any solar activity.
The occurrence frequency of coronal mass ejections and flares is strongly modulated by the cycle. Flares of any given size are some 50 times more frequent at solar maximum than at minimum. Large coronal mass ejections occur on average a few times a day at solar maximum, down to one every few days at solar minimum. The size of these events themselves does not depend sensitively on the phase of the solar cycle. A case in point are the three large X-class flares that occurred in December 2006, very near solar minimum; an X9.0 flare on Dec 5 stands as one of the brightest on record.
A solar flare is a sudden flash of increased brightness on the Sun, usually observed near its surface and in close proximity to a sunspot group. Powerful flares are often, but not always, accompanied by a coronal mass ejection. Even the most powerful flares are barely detectable in the total solar irradiance (the "solar constant").[1]
An aurora is most likely to occur during periods of high solar activity when there is a high probability of a large solar flare. When such an eruption occurs, charged particles from the flare may spiral towards earth arriving about a day later. This may or may not cause an aurora: if the interstellar magnetic field has same polarity, the particles do not get coupled to the geomagnetic field efficiently. Besides sunspot-related active solar surface areas, other solar phenomena that produce particles causing auroras, such as re-occurring coronal holes spraying out intense solar wind. These charged particles are affected and captured by the geomagentic field and the various radiation belts surrounding earth. The aurora-producing relativistic electrons eventually precipitate towards earth's magnetic poles, resulting in an aurora which disrupts short-wave communications (SID) due to ionospheric/magnetic storms in the D, E, and F layers. Various visual effects are also seen in the sky towards the north – aptly called the Northern Lights. The same effect occurs in the Southern Hemisphere, but the visual effects are towards the south. The auroral event starts by onset of geomagnetic storm, followed by number of sub-storms over the next day or so.
In late October 2003, a series of large solar flares occurred. A X17.2-class flare ejected on 28 October 2003 produced auroras visible as far south as Florida and Texas. A G5 level geomagnetic storm blasted the Earth's magnetosphere the next two days. A few days later, the largest solar flare ever measured with instruments occurred on 4 November; initially measured at X28, it was later upgraded to an X45-class. This flare was not Earth-oriented and thus only resulted in high-latitude auroras. The whole sequence of events occurred from 28 October to 4 November is known as the Halloween Solar Storm.
Flares may also occur from solar panels, but they are not as bright (up to −3.5 magnitude). Such flares last about twice as long as those from the main mission antennas (MMA), because the so-called "mirror angle" for the solar panels is twice that for the MMAs. There are also rare cases of flares from MMAs and solar panels, or two MMAs (front and either right or left) of one satellite in a single pass.