Does the Sun influence Earth's magnetic reversals?
Earth's magnetic field responds to the solar wind, but does the solar wind maintain Earth's magnetic field?
If you have ever played with magnets you know the interaction is dynamic - each magnet influences the other. That is true for the Earth's magnetic field and the solar wind. Does that interaction help to maintain Earth's magnetic field? And if the Sun is entering a prolonged period of quiet, is that destabilizing Earth's magnetic field and initiating a magnetic reversal?
The Maunder Minimum was a period from 1645-1710 when sunspots were exceedingly rare and temperatures were extremely cold. Another "grand-minimum" occurred from 1810-1838 and sunspot activity has been decreasing since 2004. Is this part of a larger cycle, on the order of thousands of years, of decreasing solar activity? If so, is this decreased interaction between the solar wind and the Earth's magnetic field weakening the Earth's magnetic field and, over thousands of years, leading to a field reversal?
First, we need a mechanism. A nail can be magnetized by a moving magnetic field. Absent the magnet, the nail gradually loses its magnetism. Since the solar wind is also a moving magnetic field, it may, in part, cause Earth's magnetic field. There are physical models of Earth's interior dynamo. How do these models respond to an external magnetic field?
Second, we need evidence: do tree rings and glacial core data show a long period cooling trend that would suggest that the Sun is in a long period of decreasing activity?
And third, an effect: what is the evidence that the Earth's magnetic field is weakening and eventually reversing over a period of thousands of years?
Cycle 24 is the weakest cycle in 100 years. This might be part of a centennial tapering of magnetic activity known as the Gleissberg cycle.
D. Hathaway / NASA / MSFC