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INTRODUCTION TO SPACE WEATHER

Most people are under the impression that space is just a hard vacuum. This could not be further from the truth! Space around the Earth is very complex and busy. Solar wind speeds can reach values of more than 1000km/s and charged particles can reach relativistic speeds (significant portions of the speed of light). Hard X-rays bathe space following solar events. These conditions are very bad for biological organisms and for the electronics on board spacecraft.

The majority of these effects are caused by our own sun. The Sun is not just a yellow disk sitting up there and providing heat to swim by. It is in fact a very active body doing some very peculiar things. For example, it swaps its magnetic field semi-periodically with the result that solar activity varies with minima and maxima coming around roughly every 11 years. On top of this, the Sun rotates in a very complex way - faster at it's equator than at it's poles which causes magnetic fields on the Sun itself to twist up into very complex patterns. Where these concentrated fields penetrate the solar "surface", temperatures, although still very high, are slightly lower than the surrounding solar surface. These darker areas are observed as sunspots from the Earth and the more sunspots we see, the higher the solar activity.

During periods of high solar activity (the last one ended around 2003 and the next one is expected to start by the end of 2010), these active areas can become so charged with energy and magnetically so complex that the magnetic fields carrying huge amounts of super heated plasma cannot be contained. These blobs of plasma are then ejected from the Sun and, if the timing is right, can cause serious damage to systems in the vicinity of the Earth. Although, luckily, only a few of these ejections are on a trajectory that will influence systems on Earth (geo-effective events), any energetic event on the solar disk facing Earth generate large amounts of X-rays which can be felt on the side of Earth facing the Sun. These X-rays, and the associated extreme ultraviolet (EUV) and ultraviolet (UV) can be very useful. X-rays and EUV ionise the Earth's upper atmosphere and form the ionosphere which helps us to communicate over long distances without the use of satellites. UV rays also help us to get a nice tan on the beach and helps with photosynthesis in plants.

Fortunately, the Earth is the proud owner of a magnetic field which acts a shield, preventing most of the charged particles from reaching Earth itself and the part of space close to the Earth where low orbit satellites are situated. People and other biological organisms on the surface would not have been able to exist, were it not for our magnetic shield. Unfortunately for medium orbit satellites and due to some interesting physical effects, charged particles collect in a layer a little higher up where medium orbit satellites (such as the GPS constellation) live. The layers where these particles are situated, are called the Van Allen belts, and satellites inhabiting this area need to be specially protected. Satellites higher up are outside the worst of these radiation belts but, when an event such as a flare, occurs in a geo-effective position, the Earth's magnetic shield is deformed when the solar wind "pushes" the shield so low that geo-synchronous satellites are exposed to the full glare of the solar wind.

When the Earth's magnetic field is pushed around, we also feel the effects on the surface. If large magnetic fields (magnets) are shaken past moving charged particles (electric currents), huge currents are induced in close-by electrical conductors, such as iron in the Earth itself, conductors such as long power lines, communications or telephone lines, sensitive magnetic devices such as power transformers and basically every thing capable of carrying an electric current. If these systems and devices are close to their working limit (such as a typical electric power distribution system), and solar events happen, they can cause, and have caused such systems to fail, leaving people and industry without power for hours or days. In the last few years we have gotten very used to high speed DSL-based internet, and many organisations are basing their distributed networks on DSL-based internet connections. These connections are, by definition being carried on copper cables susceptible to solar events. The next solar maximum is going to be a very interesting period.

It must be noted that, although solar events are concentrated during solar maxima, flares and other solar events still happen during periods of lower solar activity. In fact, one of the largest flares in history was recorded recently close to solar minimum.

Space weather affects every person on Earth and is fortunately quite predictable. Click here to look at the latest space weather conditions, or here for a longer term forecast. To look at the latest solar images, please click here. If you are interested in reading more about the subject, please click here.