The story appears on

Page A10

September 19, 2009

GET this page in PDF

Free for subscribers

View shopping cart

Related News

Home » World

Sun batters Earth with mighty winds

THE sun can lash the Earth with powerful winds that can disrupt communications, aviation and power lines even when it is in the quiet phase of its 11-year solar cycle, American scientists say.

Observers have traditionally used the number of sunspots on the sun's surface to measure its activity. The number of sunspots peaks and troughs during a cycle.

At the peak, intense solar flares and geomagnetic storms eject vast amounts of energy into space, crashing into the Earth's protective magnetic fields, knocking out satellites, disrupting communications and causing colorful auroras.

But scientists at the National Center for Atmospheric Research in the United States and the University of Michigan found that the Earth was bombarded with intense solar winds last year despite an unusually quiet phase for the sun.

"The sun continues to surprise us," said Sarah Gibson of the center's High Altitude Observatory and lead author of the study. "The solar wind can hit Earth like a fire hose even when there are virtually no sunspots.

"The fact that Earth can continue to ring with solar energy has implications for satellites and sensitive technological systems," Gibson says. "This will keep scientists busy bringing all the pieces together."

Scientists previously thought the streams of energy largely disappeared as the solar cycle approached the minimum.

Gibson and the team, which also included scientists from NOAA and NASA, compared measurements from the current solar minimum interval, taken in 2008, with data of the last solar minimum in 1996.

Although the current solar minimum has fewer sunspots than in 75 years, the sun's effect on Earth's outer radiation belt was more than three times greater last year than in 1996.

The research in the latest issue of the Journal of Geophysical Research found that the prevalence of high-speed streams during the solar minimum in 2008 appeared to be related to the sun's current structure.

As the number of sunspots fell over the past few years, large holes lingered in the surface of the sun near its equator.

The high-speed streams that blow out of those holes engulfed Earth during 55 percent of the study period in 2008, compared to 31 percent of the study period dating to 1996.

A single stream of charged particles can last for as long as 7 to 10 days, the study says.

"The new observations from last year are changing our understanding of how solar quiet intervals affect the Earth and how and why this might change from cycle to cycle," said co-author Janet Kozyra.


Copyright © 1999- Shanghai Daily. All rights reserved.Preferably viewed with Internet Explorer 8 or newer browsers.

沪公网安备 31010602000204号

Email this to your friend