‘Bubbles’ and ‘holes’ in the sun's diffuse outer layer apparently can cause as much disturbance in the earth's magnetic field as solar flares. Bubblelike clouds of erupting gas in the sun's tenuous halo, the corona, appear to be associated with the two largest storms reported so far during the present 11-year sunspot cycle. In addition to these coronal ‘transients,’ there are long-lived sources of high-speed particle streams, called coronal ‘holes,’ whose relationship to the sunspot cycle has just been described mathematically by a team of investigators at the Space Environment Laboratory (NOAA) in Boulder.
Solar flares, with their spectacular outbursts of hot gases, have a strong, but often overlooked, rival in the production of magnetic storms, namely, coronal transients. These powerful particle eruptions lack the fiery sendoff typical of solar flares, and they are often marked simply by the sudden disappearance of dark bands or ‘filaments’ of gas that are supported in the corona by strong magnetic fields.