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Re: magnetic lines like these ?



... but I am convinced that Zeilik goofed (Fig 12.9 page 139). What he
calls "magnetic lines of force" are not lines of B. If they were the Sun
would be a magnetic monopole. ...

I know it is pretentious to accuse an expert astronomer whose "research
activity currently focus on two areas: magnetic activity cycles in
sun-like stars and ..." But students have rights; I am a student who
decided to learn astronomy after many years of physics teaching.

Actually the goofing is in use the phrase "magnetic lines of force" for
something that is quite different. Was it a deliberate trick designed to
create an illusion that difficult concepts of solar magnetism are as
simple as circular B lines around wires? Selling hard-to-swallow ideas
in an attrctively looking box?

It turns out that the author deals with the subject again in chapter 13.
Spiral lines are shown again (Figure 13.14) but this time the label is
"interplanetary magnetic field". All lines are outgoing, as marked by
arrows. Why is it differnt from Van Allen's loops? The caption of the
figure is as follows.

"The spiral shape of the sun's magnetic field as it is carried by the
solar wind into interplanetary space. The outflow of the solar wind
carries a magnetic wind from the sun."

The phrase, "the sun's magnetic field is carried by the solar wind into
interplanetary space" appears in many textbooks. John D. Fox, for example,
(Astronomy, 1995) writes that "the magnetic field lines are swept outward
by the solar wind." Solar magnetic field at the time of sunspot minimum,
according to Fox, has only two poles. Many local magnetic sources, often
as intense as 3000 Gs (0.3 T) develop during solar active periods. I see
two very distinct problems here. How are magnetic fields generated and why
they do not become negligible at distances of tens or hundreds of solar
diameters. It is the second problem that I am trying to comprehand.

The textbooks imply that if the solar wind bursts were not present then
the field lines would be confined to small regions. The streams of plasma
carry magnetic fields to great distances. I am having conceptual
difficulties with such ideas. If solar wind is "carrying magnetic field
lines" away from Sun (to distances of 100 AU and more) then how the
"returning magnetic lines can be explained? Van Allen does mention some
kind of a "current sheet" (in the "New Solar System" book, 3 edition,
1990, edited by Beitty and Chaikin, page 31) but I have no idea what he
has in mind.

How can a macroscopically neutral gas (ionized) be responsible for carrying
lines of B around its paths? A single charged particle does "carry a field
with it"; it can be calculated by using the Biot-Savart formula. And it can
be detected by a charged particle at rest. But that field is not directed
along the path of the moving ion. And a combined field of many + and - ions
is zero everywhere on the macroscopic scale. Astronomy textbboks say that
ions spiral along the field lines and that by doing this they carry the
guiding field lines with them. Am I the only one who is confused?

Ludwik Kowalski