DEPARTMENT 4 : Solar Physics
SIDC - A European Space Weather Centre
White-light observations of the solar photosphere are a simple but important way to characterize solar activity. The 11-year solar activity cycle is the most prominent source of solar variability.
The existence of this cycle has been known for centuries due to observations of sunspots on the solar surface. The sunspot index is the oldest solar index measuring solar activity and is used for many studies on the cyclical behaviour of the Sun. This is why the international scientific community, through the International Council of Scientific Unions (ICSU), has repeatedly expressed its high interest in this index and committed its computation to the SIDC at the Royal Observatory.
The SIDC is a permanent service center specialized in solar monitoring and solar activity forecasting. The International Sunspot Index has been statistically deduced at the SIDC since 1981 on the basis of data provided by a worldwide network of about 80 (professional and amateur) observing stations.
Sunspots are not the only manifestation of the solar activity cycle. During solar maximum, the Sun generates a large number of energetic eruptions such as solar flares. Solar flares produce intense electromagnetic radiation and high-energy particles, and may be associated with global plasma expulsions from the solar corona known as Coronal Mass Ejections (CMEs).
These have the potential of causing severe damage to human technology in space and on the ground and to hamper communication systems. Increased fluxes of high-energy particles, for example, are detrimental for Earth-orbiting satellites and expose airplane crews and passengers to enhanced doses of radiation. Disturbances in the solar wind interact with the Earth’s magnetosphere, causing geomagnetic storms that, amongst other things, disturb GPS signals.
All these effects form part of what is now commonly called ‘Space Weather’.
The SIDC operates a service to help users reduce the impact of space weather on activities of human interest. In addition to its long-term monitoring of the solar activity cycle through the International Sunspot Number, the SIDC has since 1 January 2001 also the task of providing short-term (3-day) forecasts of solar activity and its impact on the space environment of the Earth.
The SIDC performs this task as one of the Regional Warning Centres of the International Space Environment Service (ISES).
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