Nature Of Active Region Research Articles

Ratio of calcium plage to sunspot areas of solar active regions

Published sunspot and calcium plage areas were examined for about 1,700 solar active regions (ARs) between 1971 and 1982. With these data, averaged AR properties, the possibility of energy balance between spot and facular emission over the lifetimes of activity complexes, and changes in AR properties over an 11‐year sunspot cycle were studied. Overall energy balance can neither be established nor ruled out. Apparently, real temporal changes in the nature of ARs, however, imply either that energy balance cannot hold over periods shorter than a few years or that standard models for estimating irradiance fluctuations from spot and/or plage areas must be modified.

The Sun and Nearby Stars: Microwave Observations at High Resolution

High-resolution microwave observations are providing new insights into the nature of active regions and eruptions on the sun and nearby stars. The strength, evolution, and structure of magnetic fields in coronal loops can be determined by multiple-wavelength observations with the Very Large Array. Flare models can be tested with Very Large Array snapshot maps, which have angular resolutions of better than 1 second of arc in time periods as short as 10 seconds. Magnetic changes that precede solar eruptions on time scales of tens of minutes involve primarily emerging coronal loops and the interactions of two or more loops. Magnetic reconnection at the interface of two closed loops may accelerate electrons and trigger the release of microwave energy in the coronal parts of the magnetic loops. Nearby main-sequence stars of late spectral type emit slowly varying microwave radiation and stellar microwave bursts that show striking similarities to those of the sun.