giovedì 19 gennaio 2017

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:
"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 auroras

http://spaceweather.com/

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