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November 20, 2018, 15:00 UTC

Signs of the beginning of a new activity cycle are observed on the Sun

Magnetic fields of the new 25th solar cycle Possible magnetic fields of the new 25th solar cycle. The photo was taken by the HMI telescope on the SDO satellite on 08/08/2018.


The first signs indicating the approach of a new cycle of solar activity are observed on the Sun for the past two weeks. Such signs are the magnetic fields with a different direction, different from the one observed for the last 11 years which began to appear in the northern hemisphere of the Sun at a great distance from the equator.

Although most people perceive the solar cycle as a change in the number of solar flares and magnetic storms, it undoubtedly has a much more complex nature. In particular, since flares are the explosions (that is, essentially the energy release), it is reasonable to ask, where does this energy accumulate? The answer to this question is considered to be known – the energy is stored in the magnetic field of the Sun. And since the accumulation of energy must undoubtedly precede its release, then the changes in the magnetic field must precede the solar flares. This is what happening. In particular, it is observations of the dynamics of magnetic fields on the Sun that is the main way to predict flare activity.

For this reason, it is easy to guess that behind the global 11-year-old flywheel changing the frequency of flares, should be hidden the changing flywheel of the magnetic field of the Sun. There really is such a flywheel on the Sun and it is called a dynamo-mechanism. Due to the rotation of the Sun, the lines of the magnetic field seem to be wound around it like threads on a yarn, increasing their intensity, then reaching a maximum, and then after a short pause (peak activity) beginning to spin in an opposite direction. Unwinding in this way, they pass through a minimum and without stopping continue to spin in a new direction to the next maximum. By imagining this picture, it is clear that at the minimum of the solar cycle the global magnetic field of the Sun does not simply pass through a zero but changes its direction. It is this change - is the sign of the near beginning of a new cycle. There is one more feature that cannot be easily explained without the use of formulas but is well established - the fields of the old direction always disappear near the solar equator, and new fields of a different direction always appear at high latitudes, and the higher they are, the stronger to be a new cycle is believed.

The first region of a magnetic field of a different direction was recorded on the Sun on 8 November and existed for about a day, which allowed the possibility that this was an accident. Three days ago, on 17 November, at about the same high latitudes, a new magnetic flux surfaced with the same (reverse) direction. At the moment, it is almost destroyed, but its traces are still visible on the disk of the Sun. In general, these days the behavior of our star is very similar to the stage that always precedes the start of the cycle. The reason for this "timid" behavior is that magnetic fields on the Sun are formed at a very great depth and float up very slowly and gradually. As a result, the emergence of small magnetic islands is usually preceded by a massive emergence of the field - the first regions that broke through the thickness of the solar plasma with a depth of more than 200 thousand km. Several scenarios are possible further, amongst which the rapid (within six months or a year) surfacing of the main new magnetic fluxes and pulsing start of the flywheel of flares. However, a slow increase in activity is also possible when the Sun gets stuck at the low point for 2 or 3 years. In any case, if the appearance of new fluxes is not an accident, we can conclude that the fundamental physics of solar activity is working correctly, and the conditions for a new cycle have already been formed somewhere in the depths of our star hidden from the eyes. It remains only to wait how quickly and with what intensity it will manifest itself on the surface.


Laboratory of X-ray astronomy of the Sun, Lebedev Institute, Russia
© XRAS tesis.lebedev.ru