David Archibald writes to tell me that the IMF has hit “rock bottom” and may go lower still. Watching the IMF is a good indicator of the activity of the Sun’s internal magnetic dynamo. Looking at this graph from Archibald, and Lief’s graph below one could conclude that the sun’s inner magnetics are quieter than any time in the last 90+ years.
First a bit of a primer to help our readers understand what the IMF is.
This is from SpaceWeather.com
During solar minimum the Sun’s magnetic field, like Earth’s, resembles that of an iron bar magnet, with great closed loops near the equator and open field lines near the poles. Scientists call such a field a “dipole.” The Sun’s dipolar field is about as strong as a refrigerator magnet, or 50 gauss. Earth’s magnetic field is 100 times weaker.

Steve Suess (NASA/MSFC) prepared this figure, which shows the Sun's spiraling magnetic field from a vantage point ~100 AU from the Sun.
During the years around solar maximum (2000 and 2001 are good examples) spots pepper the face of the Sun. Sunspots are places where intense magnetic loops — hundreds of times stronger than the ambient dipole field — poke through the photosphere. Sunspot magnetic fields overwhelm the underlying dipole; as a result, the Sun’s magnetic field near the surface of the star becomes tangled and complicated.
The Sun’s magnetic field isn’t confined to the immediate vicinity of our star. The solar wind carries it throughout the solar system. Out among the planets we call the Sun’s magnetic field the “Interplanetary Magnetic Field” or “IMF.” Because the Sun rotates (once every 27 days) the IMF has a spiral shape — named the “Parker spiral” after the scientist who first described it.
Here is another view of the Parker Spiral. Our own Leif Svalgaard had a hand in this I believe:

The heliospheric current sheet is a three-dimensional form of a Parker spiral that results from the influence of the Sun's rotating magnetic field on the plasma in the interplanetary medium.
The IMF goes through the floor
Guest Post by David Archibald Read the rest of this entry »
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