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The Sun is the closest star to us, and a regular object in our Galaxy.
Solar activity manifests itself, primarily, in solar flares - episodic
explosive energy release in the form of electromagnetic radiation and
high energy particles (electrons and protons). The nature of the flares
is related to cyclic variations of global and local magnetic fields in
the atmosphere of the Sun. Observations of solar radio-frequency emission
in the microwave range with RATAN-600 allow one to determine the parameters
of the plasma and therefore, measure magnetic-field strengths in the
chromosphere and corona of the Sun. Powerful flares originate in these
layers of the solar atmosphere, along with coronal mass ejections,
whereby clouds of plasma cause geomagnetic storms upon reaching the
Earth's ionosphere. As a result of mixing of matter and non-uniform
rotation of the Sun, magnetic field lines periodically "emerge" from
underneath the photosphere in the form of visual-range sunspots. When
considering other ranges - X-rays, ultraviolet, radio - we see that
the emerging magnetic tube forms a three-dimensional loop, which can
intertwine, creating bundles of strong magnetic fields, and form complex
structures with other loops. Such formations are called active regions.
When the loops interact with each other, a reconnection of magnetic
field lines occurs, accompanied by a release of accumulated magnetic
energy, and, as a result, a simplification of the magnetic structure
of the region, its break-up, and consequent disappearance of the spot.
Active regions at the solar surface "live" for several hours to several
months. The full activity cycle lasts for 11 years, whereas the Sun
rotates about its axis once every 27 days. In comparison, a large flare
lasts for only a few minutes, but the preliminary stage of the flare -
the increase of the complexity of the magnetic structure, the emergence
of new magnetic tubes - takes up to three days. During this time, one can
predict solar flares by the typical magnetic-field configuration in the
photosphere, the characteristic spectra, and the distribution of
intensity and polarization of microwave radiation. The interest in
solar activity and the geomagnetic storms that it causes is due to
the fact that the latter can affect the well-being of meteosensitive
people, and also cause various industrial problems (radio communication
interference, exposure of astronauts during space walks, transport and
commercial infrastructure, agriculture, etc.).
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Last update: 26/03/2014
