The Hindu : Tamil Nadu / Chennai News : Solar flares, radio blackouts

Online edition of India's National Newspaper
Friday, Jan 21, 2005

Tamil Nadu

Tamil Nadu - Chennai

Solar flares, radio blackouts

By Lalithasai

CHENNAI, JAN. 20. A new sunspot group has emerged across the surface of the sun. The sunspot group, assigned NOAA (National Oceanic and Atmospheric Administration, U. S.) Region number 720, was roughly 18 times the size of earth, said P. Iyamperumal, Executive Director, Tamil Nadu Science and Technology Centre.

Region 720, a large and complex sunspot cluster, has produced several strong flares. About five large solar flares were recorded by recent observations from the Solar and Heliospheric Observatory (SOHO). These produced moderate to strong radio blackouts since January 15. The largest of these solar eruptions, an X-class flare, occurred on January 17, he said.

The NOAA has carried out major studies on sunspots and the implication of flares on the earth's atmosphere and magnetosphere. According to NOAA, the flare caused signal degradation in short-wave radio communications. It also says that associated strong geomagnetic and radiation storms are under way.

Eruptions likely

Further major eruptions are possible from this region before it rotates around the visible solar disk and disappears from view on January 22.

Sunspots are dark spots, some as large as 50,000 miles in diameter, which move across the photosphere of the sun's surface contracting and expanding as they go. They are marked by a lower temperature than their surroundings and intense magnetic activity.

Although they are blindingly bright, at temperatures of roughly 5000 K, the contrast with the surrounding material at some 6000 K leaves them clearly visible as dark spots.

Sunspot activity occur in cycles about every 11 years. The highest sunspot activity point during this cycle is knows as solar maximum and the point of lowest activity as the solar minimum.

The differential rotation of the sun (it moves faster near the equator and slower near the polar regions) is thought to be the cause of the solar cycle. The sun has a magnetic field around it and the differential rotation causes the magnetic field near the equator to rotate faster than the magnetic field near the poles.

This causes a twist in its magnetic flux lines. So the magnetic field becomes concentrated near certain spots, which suppresses the outflow of hot gases in those areas.

This results in reduced temperature around that region. This cooler region on the photosphere of the sun appears as dark spots or sunspots.

When the outflow of gases is suppressed the stored up magnetic energy is released violently and suddenly near and around the sunspot region. These are called solar flares. One cannot view a solar flare by staring at the sun as it is bound to damage the eyes. Flares and sunspots are

difficult to see against the bright emission form the photosphere. Sunspot region 720 can be observed using safe methods. Another large sunspot, bigger than the size of the earth, denoted as 723 is also visible in the western limb of the Sun.

The B.M. Birla Planetarium, Gandhi Mandapam Road, Chennai, has made arrangements for the public to view the sunspots safely, using exclusive solar telescope on January 21 from 10 a.m. to 5. p.m., said the director.

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