Transient Magnetic Fields

This book is an original study aimed at understanding how vacuum magnetic fields change with time. Specifically, it describes the waves that radiate from a sphere when the electric current on its surface is turned on or off, either suddenly, gradually, or periodically.

Numerical simulations are an invaluable source of information about this and related subjects, but they are often more difficult to interpret than exact, closed-form solutions that can easily be applied to a variety of situations. Thus, the objective here is to obtain an exact solution of Maxwell’s equations in closed form—something simple, yet rigorous, which can be used as a model for understanding transient magnetic fields in more complicated situations. The work therefore stands as a self-contained solution of Maxwell’s equations for an electric current wrapped around the surface of a sphere.

This study assumes a strong background in electromagnetism or a relatedresearch area. Online animations are available for each figure to better illustrate the motions of magnetic field lines.

Dr. Sheeley received his BS (1960) and PhD (1965) degrees in physics from the Caltech in Pasadena CA. His PhD thesis was “Observations of Solar Magnetic Fields,” which was based on observations that he obtained at the Mt. Wilson Observatory under the supervision of Caltech Professor R.B. Leighton. Dr. Sheeley continued this work during 1965–1972 in the Solar Division of the Kitt Peak National Observatory, confirming his thesis result that strong magnetic fields exist outside of sunspots and discovering moving magnetic fields in the “moats” around sunspots. In 1973, Dr. Sheeley joined the Naval Research Laboratory and moved to Houston TX to take part in the operations phase of the NASA/Skylab mission. He spent 1974–1976 at KPNO in Tucson comparing these observations with Kitt Peak solar magnetograms.

In 1977, Dr. Sheeley moved to NRL in Washington DC, where he continued the Skylab data analysis and then began a long series of studies of the corona using observations with the Solwind white-light coronagraph on the P78-1 spacecraft (1979-1985), the LASCO coronagraph on SOHO (1995-), and the Secchi coronagraphs on the STEREO spacecraft (2006-). Also beginning in 1981, he used a flux-transport code developed by his NRL colleagues Dr. Jay Boris and Dr. C.R. DeVore to study the evolution of the Sun’s surface field. In 1986, he began a long-term collaboration with his NRL colleague, Dr. Yi-Ming Wang, who extended the flux-transport code into the corona. This work led to the Wang-Sheeley-Arge-enlil (WSA-enlil) solar wind and coronal mass ejection forecasting model, now on the National Weather Service website. 

In 2005, Dr. Sheeley received NRL’s E.O. Hulburt Award, and in 2009, he received the George Ellery Hale Prize of the Solar Physics Division of the American Astronomical Society. Dr. Sheeley retired from NRL in November 2016 and has been continuing his magnetic field studies in his retirement. He currently holds a Visiting Research Scientist appointment at the Lunar and Planetary Laboratory of the University of Arizona (LPL/ UA).