Solar flare produces light, radiation event on Earth

Posted: Wednesday, November 07, 2001

ANCHORAGE (AP) -- When southerners report red northern lights, it means something big probably happened the day before 93 million miles away.

University of Alaska Fairbanks scientists say a solar flare Sunday morning produced a ''coronal mass ejection'' -- a cloud of ionized hydrogen released from the sun and sent toward Earth.

About 36 hours later, a rare northern lights display put glowing red, blue and green colors into the skies as far south as Alabama, prompting queries to authorities as to whether the country were under attack.

No terrorists, just an unusual eruption on the sun.

''As these events go, it was quite a fast moving one,'' said Mark Conde, assistant professor of physics at UAF.

The sun continuously sends ionized hydrogen and other materials, called solar wind, toward the earth. When it reaches the upper atmosphere, auroral light, like a neon sign, is produced by a high-vacuum electrical discharge.

The aurora is always present, said Syun-Ichi Akasofu, former director of the Geophysical Institute at UAF. From a satellite, it appears like a kind of a ring around the north and south geomagnetic poles, he said, in the shape of a curtain. Fairbanks is under that ring in the northern hemisphere.

An eruption on the sun causes a gust in the solar wind, Akasofu said, and he compared it to applying more power to a headlamp on a bicycle-powered generator.

''If you crank the generator, the light gets brighter,'' Akasofu said.

Conde called it a solar wind shock and said it arrived at more than double the normal speed. Instead of 186,000 miles per second, the gust headed toward Earth at up to 500,000 miles per second.

''It more than doubled,'' Conde said.

The cloud also was far more dense. Particles generally reach earth at one to 10 parts per cubic centimeter, Conde said. The cloud Monday was off the scale but well over 100 parts per centimeter.

Such events reorganize the magnetic field of earth and put lots of material in the near-earth environment, Conde said.

The material reached a satellite upstream of Earth at 4:30 p.m. Alaska time on Monday. The material reached the earth about 45 minutes to an hour later.

''We just got hammered the rest of the night,'' he said.

Accompanying the relatively dense cloud of material was a radiation storm that made instruments on satellites give unreliable data, Conde said, and might have even damaged them.

If an astronaut had been working outside his spacecraft during the radiation burst, ''That would have been quite a threat to the astronaut,'' he said.

Flying through the radiation storm at high altitude on a commercial aircraft would have been the equivalent of receiving 10 chest X-rays, Conde said.

The color of the aurora depends upon what type of molecule is struck by the charged particles and at what atmospheric level.

Oxygen about 60 miles up produces a green color, the most common aurora color. Higher-level oxygen between 200 and 300 miles over the earth produces the more rare all-red auroras. Ionized nitrogen produces blue light and neutral nitrogen glows purplish-red at the edges of the aurora.

Red auroras seen in various parts of the country could have occurred because of the enormous volume of low-energy particles that were stopped higher in the atmosphere.

So much appeared, Conde said, ''I though my instruments weren't working,'' he said.

Last year and this year were the peak of the 11-year cycle of activity on the sun Akasofu and Conde said.

Fairbanks was cloudy and Anchorage foggy Monday night, limiting viewing for many Alaskans. However, scientists knew what was happening.

''The magnetometer showed quite a bit of disturbance, what we call a magnetic storm,'' Akasofu said.

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