Solar Activity

The first step in producing an auroral forecast is to look at the sun and evaluate its activity level. The level of the activity, as well as the location, play an important role when predicting whether the solar activity is geoeffective or not.

Sunspots are the most obvious region of activity. They can be see in the white light from the ground. Sunspots arise and decay on the sun with time scales of days to months. The sun rotates once around its axis in 27 days, and sometimes large groups of sunspots can be seen on more than one rotation. The number of sunspots at any given time follows an 11-year cycle. This cycle is a measure of the general activity of the sun. More information can be found at the SEC web site.
Sunspot cycle	Sunspots in visible light
Solar flares are short-lived (minutes to hours) eruptions. Flares are classified according to the energy that they radiate in the X-ray wavelengths (0.1 -0.8 nm).  There are four classifications:  B (really small), C (small), M (moderate), and X (extreme). The flares are observed from satellites in earth orbit by the sudden increase in X-ray flux, and can also be seen from satellites in the extreme ultraviolet emissions from the sun. Solar flares send out shock waves that travel through the solar wind and, if they hit earth, can generate geomagnetic storms and aurora.
X-ray flux	Extreme Ultraviolet Images
Coronal Mass Ejections (CME) are the largest events. They throw out a large amount of material from the sun's surface (usually referred to as a "magnetic cloud") which then travels with the solar wind into space. If one of these clouds hits the earth, we can expect large geomagnetic storms and significant aurora. The CMEs are best seen in observations of the solar wind, and in images taken by a satellite in white light with a disk in front of the sun to simulate a solar eclipse. They can also be seen from the ground during a naturally occurring eclipse, or with special telescopes on high mountain tops.
Solar wind from Mauna Loa	and from space