Meteorologists can no longer view the Earth as an isolated system. Both long-term climate changes and day-to-day weather show links with the Sun`s activity. Scientists therefore study the nature of those links intensely. With data from ESA`s spaceprobes SOHO, Cluster, and Ulysses, we now have the information we need to solve the mystery of how the Sun`s activity affects the climate here on Earth. This study is the first step in setting up a new type of weather forecast - the space-weather bulletin.
For the Sun to affect the Earth`s weather, the Sun`s behaviour must vary in some way. At visible wavelengths, however, the Sun is remarkably constant. Satellite data show that there are dramatic changes going on beyond this narrow range. For example, the Sun emits a `wind` of charged particles and we know that this wind is variable. The ultraviolet radiation released by the Sun also varies. Studying the interaction between solar variability and the Earth environment is a science known as `space weather`.
This solar variability is caused by the ever-changing magnetic behaviour of the Sun. The Sun`s magnetic behaviour changes on an 11-year cycle, passing from `solar minimum` to `solar maximum`. At the peak of this cycle, one of which occurred last year, the solar wind is stormy because explosions on the Sun`s surface catapult particles outwards with an increased intensity. The energy released during such explosions can be up to one thousand million megatonnes (or 66 thousand million times the energy released by the Hiroshima atomic bomb). Such events are also the source of the variable ultraviolet emissions.
ESA`s solar fleet is observing these phenomena very carefully and from several points in space. The joint ESA/NASA spaceprobe, the Solar and Heliospheric Observatory (SOHO), is constantly watching the Sun, monitoring this activity. The solar wind gusts buffet the magnetic field of the Earth. ESA`s quartet of satellites, Cluster, monitors these effects close to Earth while Ulysses patrols the Sun in a tilted orbit, well away from the plane of the planets, to get a more `global` view of the solar wind.
Alexi Glover | alfa
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