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Thursday, August 8, 2013

Sun's Magnetic Field to Reverse: triggering some new space weather

As reported by National Geographic:

The sun's magnetic field, which spans the solar system, is just months away from flipping, observatory measurements show.

"This change will have ripple effects throughout the solar system," solar physicist Todd Hoeksema of Stanford University said in a statement.

Hoeksema is the director of Stanford's Wilcox Solar Observatory, one of just a few observatories around the world that monitors the sun's polar magnetic fields.

The sun's magnetic field changes polarity approximately every 11 years during the peak of each solar cycle as the sun's inner dynamo reorganizes itself.

This next reversal—which will be only the fourth observed since tracking began in 1976—will mark the midpoint of Solar Cycle 24.

During a magnetic field reversal, "the sun's polar magnetic fields weaken, go to zero and then emerge again with the opposite polarity," explained solar physicist Phil Scherrer, also at Stanford, in the statement.

Scientists are already seeing signs of the reversal happening, and this time there's a twist: Data from Wilcox show that the sun's two hemispheres are oddly out of sync, with the North Pole already beginning to change and the South Pole racing to catch up.

Soon both poles should be completely reversed. "It looks like we're no more than three to four months away from a complete field reversal," Hoeksema said.

What Does a Reversal Mean?

A reversal of the sun's magnetic field will have consequences throughout the solar system since the domain of the sun's magnetic influence—called the heliosphere—extends far beyond Pluto. Changes to the field's polarity ripple all the way out to the Voyager probes, which are racing toward interstellar space.

A NASA depiction of the heliospheric current sheet.
Playing a central role in solar field reversals is the "current sheet," a sprawling surface that juts out of the sun's equator where the sun's slowly rotating magnetic field induces an electric current.

The current itself is small—only one ten-billionth of an amp per square meter—but there's a lot of it, and the entire heliosphere is organized around it.

During field reversals, the current sheet becomes very wavy. Scherrer likens the undulations to the seams on a baseball.

As the Earth orbits the sun, our planet dips in and out of the wavy current sheet, and the transitions can stir up stormy space weather around us.

The geometry of the current sheet can also affect Earth's exposure to cosmic rays, which are high-energy particles accelerated to the speed of light by supernova explosions and other violent events in the galaxy.

Cosmic rays pose a threat to astronauts and space probes, and some researchers say they might also affect the cloudiness and climate of Earth.

The sun's current sheet functions as a barrier to cosmic rays, preventing them from penetrating into the inner solar system. And a wavy, crinkly current sheet appears to create a better shield against these energetic particles.

Additionally, the earth's magnetic field also acts as a partial shield against the subsequent 'local' space weather generated by the sun - the combination of which provides a low radiation zone for habital life on earth.  Particles generated by the sun's electromagnetic storms that filter through the earth's magnetic shield show up as the Aurora Borealis light displays at high latitude (Arctic and Antarctic) regions.