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ESA studies the Sun-Earth climate link 
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'.
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.
Scientists are looking at three main mechanisms that may explain this Sun-Earth link for our weather and climate. Firstly, the Sun's varying ultraviolet emissions affect the production of ozone in the Earth's atmosphere, changing our ozone layer, and affecting the large-scale circulation of air. Secondly, the solar wind's gusts affect the electrical properties of the Earth's upper atmosphere which somehow affects the lower layers of the atmosphere. Thirdly, during the solar minimum, the solar wind is weaker which enables galactic cosmic rays (GCRs) to enter the Earth's atmosphere more easily. GCRs are particles that are heavier and more energetic than those carried by the solar wind and are accelerated much farther away in space. Scientists believe that the movement of GCRs, which is influenced by the solar wind, generates conditions that promote the formation of low-altitude clouds. The significance of each of these mechanisms is as yet unknown, and scientists also do not know if the mechanisms are interrelated. Every avenue is being explored.
"We have just issued an announcement of opportunity inviting the community to propose contributions to such a space-weather service." says Glover. Someday perhaps ESA will be able to help scientists, industry, and commerce understand and exploit the Sun's effect on our everyday lives. For more information, please contact:
Alexi Glover
Alain Hilgers
Clovis de Matos
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