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Thursday, February 4, 1999 Published at 21:45 GMT


Sci/Tech

Where the solar wind blows

The Sun's fiery surface

By BBC News Online Science Editor Dr David Whitehouse


A stream or charged particles billowing out from the Sun
Sunlight is not the only thing that the Sun sends to us. It also gives off a stream of particles called the solar wind that gush into space at 3.2 million kilometres (two million miles) an hour.

When these electrically charged particles reach the Earth they are funnelled to the magnetic poles. When they strike the upper atmosphere light is emitted. This is how an aurora starts.

It has been known for some time that the solar wind comes from specific regions of the Sun's surface called coronal holes but scientists have never been able to pinpoint exactly where the solar stream begins.


[ image: Soho: Closer to the Sun]
Soho: Closer to the Sun
Now new observations made by the Soho sun-observing satellite have helped solve this mystery.

American and European scientists have seen solar wind flows coming from the edges of honeycomb-shaped patterns of magnetic fields at the surface of the Sun.

These observations are presented in the new issue of Science magazine. The research will lead to better understanding of the high speed solar wind.

Source of the Nile

"The search for the source of the solar wind has been like the hunt for the source of the Nile," said Dr Don Hassler of the Southwest Research Institute, Boulder, Colorado.

"For 30 years, scientists have observed high speed solar wind coming from regions in the solar atmosphere with open magnetic field lines, called coronal holes.


[ image: 'The source of the Nile']
'The source of the Nile'
"However, only recently with the observations from Soho have we been able to measure the detailed structure of this source region inside coronal holes."

The solar wind comes in two varieties: high speed and low speed. The low speed solar wind moves at roughly a million miles per hour, while the high speed wind is even faster, moving at speeds as high as two million miles per hour.

When it reaches the Earth, the solar wind distorts the shape and structure of the Earth's magnetic field.

It can cause dramatic changes in the shape of the Earth's magnetic field, which can damage satellites and disrupt communications and power systems.

The nature and origin of the solar wind is one of the main mysteries which the Solar and Heliospheric Observatory (Soho) was designed to solve.



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