[wordup] Solar wind to shield Earth during pole flip

[Adam Shand]

From: http://www.newscientist.com/news/news.jsp?id=ns99994985

Solar wind to shield Earth during pole flip
09:30 15 May 04

Hollywood now has one less disaster scenario to worry about. The Earth, 
it seems, will be safe when its magnetic field falters during the next 
reversal of its magnetic poles.

A new model of the way the Earth interacts with the solar wind 
indicates that a replacement field will form in the upper atmosphere 
during the switch.

Scientists had previously thought that the planet would be left without 
a protective shield to stop lethal radiation from space reaching the 
surface.

The strength of the Earth's magnetic field is known to drop during 
"magnetic reversals", when the north and south poles swap places. 
Records of the field direction, frozen into sediments laid down on the 
seabed, show that the magnetic field has reversed hundreds of times in 
the past 400 million years.

In normal circumstances, the magnetic field protects the Earth's 
surface from dangerous high-energy particles, including particles from 
the sun and cosmic rays from deep space.

But as the field switches polarity, it can drop to below 10 per cent of 
its normal strength for thousands of years. Such a weakened field would 
allow lethal radiation to reach the Earth's surface, with potentially 
disastrous consequences for the atmosphere, the climate and 
particularly for life.

Opportune moment

In a paper to be published in the journal Astronomy and Astrophysics, 
Guido Birk and Harald Lesch of the University of Munich, Germany, and 
Christian Konz of the Max Planck Institute for Plasma Physics in 
Garching report an investigation of exactly what happens when the field 
is drastically reduced or vanishes altogether.

Their simulations show that the solar wind - the 
million-kilometre-an-hour stream of hydrogen and helium nuclei from the 
sun - wraps itself around the Earth in a way that induces a magnetic 
field in the ionosphere as strong as the original field.

"We were quite surprised about its effectiveness," Lesch says.

The news comes at an opportune moment. The Earth's magnetic field is 
showing worrying signs that it is about to reverse again. Not only has 
the magnetic north pole wandered by 1100 kilometres in the past 200 
years, but its strength is dropping at a rate of 5 per cent a century.

"This is the fastest decrease since the last reversal 730,000 years 
ago," Lesch says.