How far apart are the Sun's magnetic field lines?
"Hi I am wondering about the Sun's magnetic field lines: 2 part question. 1) How far apart are they at the "surface" (or near) of the Sun? 2) How far apart are they when they reach the Earth's magnetopause? This would be under "normal" conditions, say with SW @ 400km/s. Any help on how this is determined would also be great!"
Magnetic field lines are kind of like lines of latitude or longitude on a globe - they are useful but imaginary concepts that help us think about something we cannot see. Magnetic fields are continuous, not discreet. Field lines are computed to show how magnetic fields connect different places, but they don't show the entire field. Hot structures in the Sun's atmosphere glow brightly and look like loops; they are connected along magnetic field lines. These clusters are called flux tubes. But we only see material that is hot and fairly dense that lies along certain field lines in certain tubes. So this question is a little hard to answer in a meaningful way.
The magnetic field elements on the Sun are concentrated in different places. The field elements arise in granules, quickly move to lanes between granules, and gradually (over a day or less) move to the boundaries between supergranules. The granules are about 1000 km across and supergranules are 30,000 km across. So in some sense you can think about the flux tubes (clusters of magnetic field) being separated by 1000 or 10,000 kilometers on the solar surface. Sunspots can be as big or bigger than supergranules and magnetic field comes from everywhere inside the spot, so they aren't really separated at all.
At Earth the magnetic field is fairly continuous too, so again it doesn't really make physical sense to think about how far apart field lines are. One way to think about it though is that the Sun rotates at 2 km/s. At that rate the opposite sides of a supergranule separated by 20,000 km would take 10,000 seconds to rotate beneath the sub-earth point, about 3 hours. There are some suggestions that solar wind quantities reflect time periods like 2-3 hours, so that makes some sense.
How far apart are these structures? Well, the Earth is about 200 solar radii from the surface, so things that took up the same angle at Earth would be about 200 times as far apart at 1 AU as they are at the surface.
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