This review discusses methods for determining solar coro-nal magnetic elds, with an emphasis on radio measurements of eld strengths in solar active regions.

Observations of sunspots, active regions, filaments, coronal arcades, and interplanetary magnetic clouds indicate that the Sun preferentially exhibits left-handed, negative-helicity features in its northern hemisphere, and their opposite counterparts in the south, independent of sunspot cycle. We investigate quantitatively the generation of magnetic helicity by solar differential rotation actin...

This review examines current eeorts to nd nd and exploit more powerful methods of measurement of the magnetic elds of the Ap stars. The methods now being explored include (1) the measurement of various moments of spectral lines in intensity and polarization spectra, and their interpretation in terms of moments of the observed elds, and (2) eld mapping by direct comparison of synthesized lines w...

We have investigated the relationship between magnetic activity and coronal structures using soft X-ray data from the Yohkoh soft X-ray telescope and magnetic field data from the Kitt Peak Solar Observatory for the period of 1991–2001 and EUV data from the Solar and Heliospheric Observatory EUV Imaging Telescope for 1996–2001. The data are reduced to Carrington synoptic maps, which reveal two t...

Knowledge about the magnetic eld distribution in radio frequency coils is important for both magnetic resonance imaging and magnetic resonance spectroscopy. The information about the eld's distribution is used to obtain correct excitation pulse ip angles, as well as to perform signal strength corrections. Another use is also accelerating imaging and spectroscopic examinations, where accurate de...

The rst extrasolar planets were discovered in 1992 around the millisecond pulsar PSR 1257+12. We show that recent developments in the study of accretion onto magnetized stars, plus the existence of the innermost, moon-sized planet in the PSR 1257+12 system, suggest that the pulsar was born with approximately its current rotation frequency and magnetic moment. If so, this has important implicati...

Motivated by the problem of the formation of active regions from a deep-seated solar magnetic field, we consider the nonlinear three-dimensional evolution of magnetic buoyancy instabilities resulting from a smoothly stratified horizontal magnetic field. By exploring the case for which the instability is continuously driven we have identified a new mechanism for the formation of concentrations o...

We self-consistently derive the magnetic energy and relative magnetic helicity budgets of a three-dimensional linear force-free magnetic structure rooted in a lower boundary plane. For the potential magnetic energy we derive a general expression that gives results practically equivalent to those of the magnetic Virial theorem. All magnetic energy and helicity budgets are formulated in terms of ...