X-rays
The activity on the Sun can be measured by its emitted X-radiation. The intensity of the X-radiation is measured in watts per square meter and is divided into classes for clarity: A, B, C, M, and X. Additionally, the individual classes are further subdivided by writing a decimal value after the class. This results in the following NOAA classification of the X-ray flux:
| Klasse | NOAA-Klassifizierung |
| < M1 | - |
| M1 - M5 | R1 - Minor |
| M5 - X1 | R2 - Moderate |
| X1 - X5 | R3 - Strong |
| X5 - X10 | R4 - Severe |
| > X10 | R5 - Extreme |
Source: NOAA/SWPC
The GOES satellites measure the current X-ray flux and provide their data in real time. The following two diagrams show the current X-ray flux of the last 6 hours (left) and 3 days (right) and indicate the intensity with color. If the graph is in the green area, the X-ray flux is low; if the curve is in the yellow or red area, the X-ray flux is high. The original data comes from the GOES satellites of the SWPC (NASA): X-Ray Flux
Live Plot
GOES X-Ray Flux (6 hours)
Live Plot
GOES X-Ray Flux (3 days)
X-ray flares (X-Ray Flares)
Flares are eruptions on the solar surface where radiation (including X-rays) is emitted and material (particles) is expelled, known as coronal mass ejections (CME). The X-rays travel at the speed of light and can be measured by satellites a few minutes after the eruption. These outbreaks appear in the diagrams of the GOES satellites as a sudden rise in the curve and end in a "peak". The more intense an eruption, the more the peak shifts into the red area. The peak of the peak is considered
The particles, on the other hand, take about two days to reach the Earth and can then cause auroras. Not every eruption results in a CME. For the aurora to occur, as much material as possible should be hurled toward Earth.
The occurrence of auroras depends on the following factors, among others:
- Flare class
If an X-Class Flare has occurred, the further development should definitely be monitored. Often, shortly thereafter, an aurora alert or a watch is issued. But even M or even C-class flares have already caused auroras. - Flare duration
The longer a flare lasts, the more energy is released. In the case of extremely prolonged flares, they are called Long Duration (LD) Flares.
Example: LD Flare on 22.09.2011
In contrast a very short flare. - Speed
The faster the mass ejection is moving, the higher the chances for auroras on Earth. The SWPC regularly provides speed analyses in their warnings for current flares. - Direction
The more central a flare occurs, the more likely it is that the expelled material flies toward Earth. If a CME is seen completely encircling the solar disk on the LASCO C2/C3 instrument of the SOHO satellite, it is called a so-called Full-Halo CME.
Impulsive Flares
Impulsive flares are very short and intense outbursts from sunspot regions. Because they are very brief, they do not have enough energy to produce a CME.
Example
Long Duration (LD) Flares
LD flares extend over several hours and have a relatively long decay. In the H-alpha range, it can be seen that the entire sunspot group lights up. These flares have a lot of potential and produce strong CMEs.
Hyder Flares
Hyder flares occur when filaments fall onto the solar surface. Due to the strong temperature differences, the matter literally explodes and produces strong mass ejections (CMEs). See filament eruption.
Examples of X-ray Flux
Strongest recorded X-Ray Flare so far (X-28 - approximated - on 04.11.2003)
Complete X-Ray Flux in 2004
M-Class Flares Early March 2011
Coronal Mass Ejection (CME)
As already described above, it is important that during a flare as much matter as possible is ejected towards Earth. The emitted matter of a CME can be seen in the images from the LASCO instrument on the SOHO satellite.
Live Plot
SOHO - LASCO C2
Live Plot
SOHO - LASCO C3
LASCO stands for Large Angle and Spectrometric Coronagraph and usually provides the first indication of the occurrence of a CME. If a strong central flare occurs, the above images should be monitored and a Full-Halo CME should be looked for. The second photo below shows a beautiful Full-Halo CME from August 16, 2001. A Full-Halo CME can also occur if the CME happens on the side facing away from Earth.
In extremely strong CMEs, "snow formation" occurs in the satellite images. A nice example of this can be found in the 3rd image below. The reason for the snowstorm is that the sensitive CCD chip simply receives too many photons and energy.
Examples
Sideward directed CME, captured by the SOHO spacecraft
Earth-directed Full Halo CME on LASCO C3
"Snow" on LASCO C3 caused by a strong proton event