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| The solar magnetic field |
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The interior of the Sun below the photosphere is not directly observable in any spectral regions. Its outermost layer – called the convection layer, has a variable rotational period.
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The Sun’s magnetic field is formed by electric currents on the borders between the convection layer and the radiation layer below. In this region we have layers with different rotational speeds.
The solar magnetic field (Bo) is ~ nearly 104 times stronger and varies much more than the Earth’s field. Thus, Bo is much more complicated than the Earth’s magnetic field and it is still not well known.
We can obtain some information about Bo by studying the light emitted from the Sun’s photosphere atoms. The Zeeman effect states that lights emitted from atoms in a magnetic field, radiated with two different wavelengths, slightly above and below the original one when the magnetic field is zero. The difference in wavelengths is proportional to the strength of the magnetic field. |
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The magnetic field lines on the Sun seem to come together in the sunspots, which act as a magnetic pole. The field strength of sunspots is typical 0,1 to 0,4 T, whereas fields otherwise on the Sun’s surface are about 0.01 T.
In a sunspot group the leading spot and the accompanying one have opposite magnetic polarity. In a given sunspot period, all leading spots on the northern hemisphere are magnetic north poles, while all spots south of the equator are south poles. In the next sunspot cycle, the situation is reversed. That is why many today conclude that the Sun’s sunspot period is about 23 years – i. e. 2 sunspot cycles.
The figure illustrates the spiral-shaped magnetic field lines (blue lines) in uniformly expanding solar wind (white lines). The Sun, the Earth’s orbit and its magnetosphere are also shown in this illustration. The solar wind blows out in all directions, and a small fraction of these particles hit the Earth. |
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