EARTH'S MAGNETIC FIELD
EARTH'S MAGNETIC FIELD RINGS LIKE A BELL: In
the Lofoten Islands of Norway, Spaceweather.com reader Rob Stammes
operates a magnetic observatory. Twenty-four hours a day, he measures
the strength and direction of the local magnetic field as well as
electrical currents running through the ground. During geomagnetic
storms, his chart recordings go haywire. On Jan. 13th, something different happened. They rang like a bell:
http://spaceweather.com/
"For about an hour,
electrical currents in the ground beneath my observatory flowed back and
forth with a sinusoidal period near 2 minutes," says Stammes. "This is
rare."
These are natural
ultra-low frequency oscillations known to researchers as "pulsations
continuous" (Pc). The physics is familiar to anyone who has studied
bells or resonant cavities. Earth's magnetic field carves out a cavity
in the surrounding solar wind. Gusts of solar wind can make the cavity
"ring" akin to a bell (references: #1, #2, #3).
Human ears cannot hear this ringing; it is electromagnetic rather than
acoustic. The physical effect is felt beneath our feet. As the cavity
vibrates, magnetic fields swing back and forth, causing electrical
currents to flow through the ground below.
The Pc waves Stammes
detected are a variety known as Pc4, which oscillate in the frequency
range 6.7–22 mHz. Such waves are good at energizing particles trapped in
Earth's magnetic field and often cause local outbursts of bright aurorashttp://spaceweather.com/
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