Universitas Helsingiensis

The quarterly of the University of Helsinki
Storm in space
Besides light and heat, the Sun also provides our planet with more exotic things. Space storms are the cause of many problems but also produce enchanting auroras.

Virve Pohjanpalo

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Solar wind – sounds beautiful, like a gentle breeze on your skin. However, we do not feel the real phenomenon on our skin, which is a good thing. The distance between the Sun and the Earth, and the Earth’s magnetosphere and atmosphere, protect us from the stream of ionised particles that the outermost layer of the Sun, or the corona, hurls into space.

Whenever the protons and electrons of the solar wind manage to slip through our magnetic shield into the atmosphere, they are manifested as auroras, or polar lights. Comets are also illustrative of the solar wind: their tails are blown away from the Sun by the solar wind particles.

The more direct observation of the solar wind takes place, for example, with the aid of satellites and space flights. Coronal mass ejections are in turn studied with a coronagraph, the operations of which are based on artificial solar eclipses. “Analysing ejections approaching the Earth directly is, however, frustratingly difficult,” says astrophysicist Emilia Huttunen, whose doctoral dissertation was publicly examined on the Kumpula Campus last year.

Space walking prohibited!

The time it takes for coronal mass ejections to reach the Earth is from two to four days, but the exact moment of the space storm caused by the ejection cannot be predicted. The predictions may fail by even dozens of hours, because the speed of the mass ejection hurtling towards the Earth is not known, nor is it known which part of the mass ejection is causing the disturbances.

However, accurate predictions would be helpful for many. Space storms cause headaches for, for example, air traffic controllers, who have to re-route cross-polar traffic.

“Otherwise the passengers would be exposed to excessive radiation and the radio contact of an aircraft could not be secured. The magnetic storms present an even greater risk to the sensitive measuring equipment of space probes and astronauts conducting space walks. The measuring equipment in space probes cannot be constantly turned away from the stream of particles, just to be safe,” Huttunen explains.

Compressed plasma

Emilia Huttunen had more accurate Sun observation in mind, when she moved her home across the Atlantic and the American continent to work at the University of California, Berkeley. “Berkeley is involved in the Solar Terrestrial Relations Observatory project, or the STEREO, and I had the opportunity to carry out computing work and data analysis for it. The project is building a satellite comprising two solar observatories. The purpose of the STEREO satellite is to provide three-dimensional measurements of the Sun – for the first time ever in the history of solar research.”

The project was, however, postponed, and Huttunen was unexpectedly able to focus on basic physical research into solar wind, and particularly on a phenomenon known as magnetic reconnection, which is the key mechanism in the coupling of solar wind with the magnetosphere. “When the opposing field lines in a magnetic field merge, the topology of the magnetic field may change. This causes a sudden release of stored magnetic energy,” Huttunen says.

Before her return to Finland, Huttunen will have the chance to concentrate on the wonders of the STEREO satellite. The goals for the satellite form a continuation to her doctoral dissertation, which analysed the causes of magnetic storms and characterised the different types of storms.

500 kilometres per second

“One space storm driver I have studied is the magnetised plasma cloud, called ejecta, originating from the coronal mass ejections,” Emilia Huttunen says. “The other storm driver I study – known as the sheath region – is occupied by solar wind plasma which the ejecta pushes forth like a snowplough.”

The sheath region’s compressed, heated plasma shakes the entire magnetosphere, while also causing significant disturbances in the electric fields and currents in the ionosphere, the outermost layer of the atmosphere. The sudden alterations in the electric field associated with the sheath region have the strongest impact at high latitudes.

The speed of the solar wind near the Earth is usually approximately 500 kilometres per second and its density a couple of particles in a cubic centimetre, but a sheath region generates a much denser stream of particles.

Ejectas, in turn, with their gradually changing magnetic fields, cause intervals of steadier dissipation of the solar wind energy into the magnetosphere. “In theory, ejectas can be predicted by observing the structuring of the magnetic field at the source of the ejection at the Sun.

In reality, there is still a long way to go before viable predictions can be presented. “There is also quite a bit to discover in the dynamics of our own magnetosphere,” Huttunen says, “And even more in the sheath regions.”

Emilia Huttunen: Interplanetary shocks, magnetic clouds and magnetospheric storms. 142 p. Finnish Meteorological Institute Contributions, Helsinki 2005. ISBN 951-697-609-3 (paperback), 952-10-2361-9 (pdf) http://ethesis.helsinki.fi/

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