Du plasma éjecté dans l'atmosphère solaire

Coronagraphs and SiRGraFs to decipher the dynamics of the solar corona

A coronal mass ejection where EMC is a huge solar plasma cloud expelled into the atmosphere during a powerful solar flare. During an EMC, several tons of matter are propelled out of the solar corona by powerful background winds. It also generates magnetic field lines causing strong geomagnetic storms.

The storms caused by these EMCs are at the origin of the polar aurora. the breath of this ejection can seriously affect the earth and hit her head-on. This is why scientists want to closely monitor these material ejections on the solar corona.

A coronagraph on board the satellite OSO-7 allowed them to observe and study this phenomenon for the first time in 1971.

Coronagraphs are used to study EMCs

All solar events do not necessarily cause coronal mass ejections. These powerful plasma projections are only possible when the solar storms are really strong. Medium power solar flares that extend over long periods are also able to generate EMCs.

The photos taken by the coronagraph made it possible to analyze what is happening at the level of the atmosphere of the Sun during these explosions of materials. Because coronal mass ejections take place in the atmosphere, the coronagraph had to eclipse the core of the sun with a disc to be able to capture pictures of the solar corona.

SiRGraFs highlight structures at low light intensity

the radial gradient of solar corona intensity complicated the observation of low light structures on the surface of the sun. They are all the more difficult to analyze on photos taken in real conditions.

To solve this brightness and contrast problem, from indian scientists from the Aryabhatta Research Institute of Observational Sciences (ARIES) developed a method to retouch the photos taken by the coronagraph. This process known as Simple Radial Gradient Filter (SiRGraF) is done in two steps.

It consists first of blur photo background captured by the coronagraph in order to separate the constant background from the transient corona. This step aims to highlight the dynamic crown of the sun.

Then a uniform azimuth background will allow the radial reduction of the luminous intensity of the elements which still shine on the photo. The combination of these two step made it possible to highlight structures with low light intensity such as coronal mass ejections.


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