The different types of solar flares
Presentation Belgian Solar Section - 28 September 2002
Last update: 28 September 2002
Contents
Origin
- The underlying cause of all flares is thought to be a reconnection (= restructuring) of magnetic fields
- During these eruptions, there is a release of:
- An amount of energy
- Throughout the entire EM-spectrum
- Mostly also an amount of material
- Surges, sprays, coronal mass-ejection (CME)
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Ha-flares
- Generalities
- Optical classification-system based on area (importance) and brightness
- 2 alfa-numerical signs, e.g. 1N
- Maximum: 4B; Minimum: SF (Subflare)
- Especially the estimation of maximum brightness is subjective
| Importance | Ac ( MH ) | Ac ( °2 ) | Ac ( 106 km2 ) |
|---|
| S | 10 < Ac < 100 | 0,2 < Ac < 2,1 | 30 < Ac < 304 |
|---|
| 1 | 100 < Ac < 250 | 2,1 < Ac < 5,2 | 304 < Ac < 761 |
|---|
| 2 | 250 < Ac < 600 | 5,2 < Ac < 12,4 | 761 < Ac < 1826 |
|---|
| 3 | 600 < Ac < 1200 | 12,4 < Ac < 24,7 | 1826 < Ac < 3653 |
|---|
| 4 | 1200 < Ac | 24,7 < Ac | 3653 < Ac |
|---|
| Category | Brightness (%) | Bandwidth | Visual |
|---|
| F (faint) | 160 < h < 260 | 0,08 nm < b < 0,12 nm | Normal |
|---|
| N (normal) | 260 < h < 360 | 0,12 nm < b < 0,20 nm | Bright |
|---|
| B (brilliant) | 360 < h | 0,20 nm < b | Brilliant |
|---|
Example: NOAA 8858, 3B, 05 Feb 02 19:26 UT
- Specials
- (Double) Ribbon flare
- Reconnection heats the footpoints of the flare at each side of the neutral line running through a sunspotgroup
- Flare visible as 2 bright, parallel bands
- Hyder-flare
- Flare that is not linked to an active group, but to the disappearance of a filament
- Flare-index
- Index (Q) based on the intensity and the duration of a Ha-flare
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Rontgenflares
- Generalities
- Objective satellitemeasurements since 1969 (GOES)
- Independant of the flare-position and the observer
- In contradiction to Ha–flares, the peakvalue of the X-ray flare is more correlated with impacts on Earth (aurora,…)
| Peak Flux Range (0,1 - 0,8 nm) |
|---|
| Class | Energy (W/m2) |
|---|
| A | Max < 10-7 |
| B | 10-7 < Max < 10-6 |
| C | 10-6 < Max < 10-5 |
| M | 10-5 < Max < 10-4 |
| X | 10-4 < Max |
Example: NOAA 9236, X2.3, 24 Nov 00, piek @ 15:13 UT
- Specials
- Highenergetic flares
- X-ray flares with a piekflux of M5 or higher
- Flare-fluence (or integrated flux)
- Total amount of radiated energy / m2 (J/m2)
- Impulsive flare
- Decreases in less than 1 hour to less than 10% of max
- Homologue flare
- Flares of about equal strength occuring in about equal timeperiods (in same sunspotgroup)
- Requires a continuous / stable energy-influx
- Suggest a triggermechanism
- White Light Flares
- Rare phenomenon, viewed for the first time in 1859 by Carrington & Hodgson
- Originates sometimes with highenergetic X-ray flares
- The released energy is so huge that it becomes visible in visual light (photosphere)
|  |
- Protonflare
- Occurs sometimes with energetic flares
- The number of protons suddenly increases with a factor 100 to > 10.000
- Looks as if, during the flare, a part of the magnetic loops is (temporarily) broken, letting escape the protons freely
- Protons travel at almost the speed of light => High energies
- Can cause major malfunctions in satellites (bit-changes, loss of pointing star,…)
Example: X5/3B flare of 14 Jul 00 by NOAA 9077 (image: SOHO)
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Radioflares
- Generalities
- Discovered during WOII (1942)
- Originate when material from an explosion on the Sun, is moving through the surrounding corona. This induces radio-emission.
- Can be observed from Earth’s surface through radiowindow (l = 1mm tot 20m)
- Mostly measured at l = 10,7 cm (2.800 MHz), 11,1 cm (2.695 MHz), 122 cm (245 MHz)
- The 10,7 cm radioflux varies between 70 sfu (cycle minimum) and about 250 sfu (cycle maximum).
- If the peak of a radio-flare attains a value that is twice the preflare background, then it is called a Tenflare.
Example: X1,5 by NOAA 10095 on 30 Aug 02
- Radiosweeps
- With a radio-spectrographe, a high number of frequencies can be scanned (“sweep”ed) in a very short time (e.g. Hiraiso, Culgoora)
- There exists 5 types of radio-sweeps, of which especially type II & type IV are of importance to determine if a flare will be geo-effective
- Type II occurs especially with flares that have ejected material (CME)
- Type II has a “double” because of internal particle-bouncing
- Because the density of the corona decreases with increasing height, the frequency also diminishes with time. Hence, the speed of the shockwave can be determined and thus also when the perturbation will reach Earth.
- Type IV occurs mostly at the same time as a type II. Stationary types IV are living the longest, do not change in frequency, and usually accompany protonflares.
- Type III is fastmoving and somewhat connected to highenergetic electrons.
Example: Types radiosweeps, en voorbeeld van Type 2 & 3 radiosweep
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Sources
- IPS (Australië) - IPS
- NOAA (“The Weekly”, plots, data,...) - NOAA
- Solar Terrestrial Dispatch - STD
- Space Weather & Radio Propagation Course
- Satellites
- Radio-astronomy
- Websites of Culgoora, Hiraiso, Ondrejov
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