Coronal Magnetism

Monday, June 18, 2018

BC Low elaborates on the extraordinary sixty years of progress made to space observation of the Sun, solar wind, planets and their magnetospheres. He notes that space platforms complementing ground-based observatories have transformed solar physics.

MLSO total eclipse, 1980 February 16, India image
MLSO total eclipse, 1980 February 16, India.

In the sixty years following E. N. Parker's prediction of the existence of the solar wind and magnetic origin of coronal heating, space borne and ground based observations have built a conceptually complete phenomenology of the corona as a fully-ionized hydromagnetic atmosphere responding in step to the global magnetic reversals of the Sun in eleven-year cycles. This phenomenology is reviewed with the theoretical ideas it motivated, describing photospheric emergence of new-cycle magnetic fluxes of a reversed polarity into the corona, ubiquitous coronal heating, hydromagnetic self-organization, explosive energy release, and the breaking of self-confinement into flows of expansion winds and episodic ejections of magnetic structures. High electrical and thermal conductivities at coronal million-degree temperatures play central roles. The corona obeys a hemispherical rule unchanging in the past four solar cycles that self-organized structures have a statistical preference for left and right-handed magnetic twists, respectively, in the northern and southern hemispheres defined relative to the rotational axis. It is pointed out, perhaps for the first time, that this hemispherical rule is built into Parker's 1955 dynamo, straightforward to deduce graphically from his book Cosmical Magnetic Fields (1979). It seems solar physicists have reached a broad-brush physical understanding of the corona solar-wind system as the prototype of a universal astrophysical phenomenon.

Author's Name: B.C. Low; Publication Name: The Sun: A Guide to Stellar Physics