What is a Solar Flare?

Solar flare is one of the most violent eruption phenomena that occurs in local areas of the solar atmosphere. It releases a large amount of energy in a short time, causing local areas to instantaneously heat up, emitting various electromagnetic radiation outwards, and accompanied by sudden enhancement of particle radiation.

On the morning of September 1, 1859, British astronomy enthusiasts

According to different observation methods, it is mainly divided into optical flare and X-ray flare. usually,

The duration of the flare is from a few minutes to several tens of minutes, but in this short time, it can release a huge energy of 10 ²⁰ to 10 ²⁵ joules, which is equivalent to about ten billion giant

The size of the flare area is an important index of the size of the flare radiation. Internationally, the area when the flare brightness reaches a maximum is used as the main basis for the flare level, and the maximum brightness of the flare is described qualitatively. According to the size of the H monochromatic light area of the flare, the optical flare is divided into five levels, which are represented by S, 1, 2, 3, and 4, respectively. Adding F, N, B after the level indicates whether the maximum brightness of the optical flare in the H line is weak, normal, or strong. So the largest and brightest flare is 4B, and the smallest and darkest is SF.

Classification of optical flares

Optical flare level	Flare area ( Unit: 10 -6 solar hemisphere area )
S	<100
1	100 250
2	250 600
3	600 1200
4	> 1200

The Earth's ionosphere is sensitive to changes in the intensity of the sun's soft X-ray radiation, so soft X-ray radiation intensities of 1-8 angstroms are also widely used internationally to rank X-ray flares. At present, the flares are divided into five levels according to the magnitude of the soft X-ray peak flow observed by the US GOES satellite, which are A, B, C, M, and X, and the released energy increases in turn. The numerical values after the levels indicate specific values of the peak X-ray flux. For example, the M2 level indicates that the peak flare soft X-ray peak flow is 2 × 10 ^-2 watts / square meter.

Generally speaking, flares below the C level are small flares; M-level flares are medium flares; X-level flares are large flares.

From the end of October to early November 2003 during the Halloween solar storm (named after the Western Halloween period), a series of large flare events erupted on the sun. Among them, the X28-level flare that broke out on November 4 was the largest flare since the GOES satellite observation.

X-ray flare classification criteria

X -ray flare level	X -ray peak flow ( Unit: W / m2 )
A	<10 -7
B	10 -7 10 -6
C	10 -6 10 -5
M	10 -5 10 -4
X	> 10 -4

The frequency of flares varies with

Flare prediction is based on three levels of C and below, M and X, and the flares are within 1 to 3 days.

The delimitation of the flare alert level is usually characterized by the solar X-ray flux observed by a geosynchronous orbit satellite, where the ray flux refers to the radiant energy of the solar X-rays received from 0.1 nm to 0.8 nm per unit time and unit area. The unit is W / ^m2 . Different levels of solar X-ray flux indicate different levels of X-ray flares. A ray flux greater than 10 ^-3 watts / m ² is a strong flare and a red alarm is issued; a ray flux greater than 10 ^-4 watts / m ² is a medium flare and an orange color. Alarm; ray flux greater than 10 ^-5 W / m ² is a weak flare and yellow alarm is issued. Solar X-ray flares cause an increase in the ionospheric electron density on the sun's surface of the earth, affecting short-wave radio communications and low-frequency navigation systems. The higher the level of flares, the more severe the impact on short-wave communication and low-frequency navigation systems.

Alert level	Index range	Possible impacts and hazards
Red alert	Ray flux 10 -3	Communication: The short-wave radio communication in most areas of Xiangyang surface was interrupted for 1 hour to 2 hours, and the signal disappeared; the low-frequency navigation signal was interrupted for 1 hour to 2 hours, which caused small interference to Xiangyang surface satellite navigation.
Orange alert	10 -3 > ray flux 10 -4	Communication: Short-wave radio communication is affected in a large area, and the signal on the sunny side is lost for about 1 hour, and the strength of the low-frequency radio navigation signal is reduced for about 1 hour.
Yellow alert	10 -4 > ray flux 10 -5	Communication: The attenuation of short-wave signal strength on the sunny side is small, and the strength of low-frequency navigation signals is short-term attenuation.
Note: Ray flux unit: W / m2