Eos, Transactions American Geophysical Union

From D. Stern



The contrasting careers of Sydney Chapman and Hannes Alfvén make an interesting story of genuine insights, false leads, bitter controversy and two very different approaches to the riddle of the magnetic storm. Unfortunately the recentEos article by S.-I.Akasofu [2003] blurs the picture, leaving readers to wonder what exactly did happen. Because of space limitations, this attempt to untangle the plot must be rather brief, but readers are urged to consult Stern [1989] (which cites the original articles), Alfvén [1939 (1970)], Dessler [1984], and Smith [1963], none mentioned by Akasofu.

Magnetic storms—so named by Alexander von Humboldt—were recognized in the 1830s as worldwide disturbances, thanks to the worldwide observatory network Humboldt helped establish. A magnetic disturbance implies an electric current somewhere, and the worldwide character suggested this current circulated around the Earth's equator. Adolph Schmidt in 1916 named it the ring current; it seemed to establish itself during magnetic storms, then decay within 1–5 days. In addition, large magnetic storms were accompanied by big displays of polar aurora, extending far equatorward from the auroral zone.