This may sound like the plot of a new low-budget science fiction movie, but based on the recent observations, it's clear that the sun's magnetic field is preparing to flip polarity.
The sun looks to be constant to us here on Earth, but it actually goes through cycles of activity. This year, 2013, is one of the peak years of its 11-year cycle (the last one was in 2002). Along with the increased number and strength of sunspots and solar flares, the peak in the cycle also means that the sun's magnetic field will flip. Currently the field points north, like Earth's magnetic field does, and by some point before the end of this year, it will switch to pointing South.
Science@NASA put together a great video to explain the whole thing:
One thing to emphasize about this whole event is that it's completely normal. It happens every 11 years. We've made it through innumerable reversals without a hitch, so unlike a sci-fi movie, this isn't going to cause any catastrophes. Another is that it happens very slowly, with the magnetic field reaching its full 'peak' of magnetic polarity sometime around the solar minimum (so, about 5-6 years from now). This is just when it crosses the line between 'negative' and 'positive'.
The only thing unusual about this particular switch is that the northern hemisphere has already switched and the southern hemisphere is lagging behind. This is something for scientists to puzzle out, since it's a little unusual, but it adds a note of interest to an otherwise rather mediocre solar maximum.
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One of the interesting things about this magnetic field reversal, though, is that it will actually make it easier for the solar wind and for coronal mass ejections to reach our atmosphere, thus giving us very active auroras. This is because of the interaction between the magnetic fields of the sun and Earth. Currently, both magnetic fields point north, so just like in the case of two bar magnets placed beside each other, both pointing in the same direction, the magnetic field lines of the two never touch. However, when the sun's field flips, the magnetic field lines of it and Earth will actually link up.
The magnetic fields of both the sun and Earth are quite weak, though. The sun's is about as strong as a refrigerator magnet, and the Earth's is quite a bit weaker than that. So, again, no sci-fi catastrophes are in store for us.
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