The sun has an 11-year activity cycle, reaching what scientists call the solar maximum. This year’s peak is weaker than others in recent history.

January 01, 2014

The sun has undergone a “complete field reversal,” with its north and south poles changing places as it marks the midpoint of Solar Cycle 24. While it may seem like the event could have catastrophic repercussions for the galaxy, its effects are actually more subtle, mostly interfering with space exploration. “Cosmic rays are a danger to astronauts and space probes, and some researchers say they might affect the cloudiness and climate of Earth,” said Phillips.

Magnetic field of earth

Both the aurora borealis and its southern counterpart – the australis – are set to become broader, more frequent, and more visible now that the event has reached its final stage. The process has been slow and steady, with solar physicist Todd Hoeksama telling Metro: “It’s kind of like a tide coming in or going out. Each little wave brings a little more water in, and eventually you get to the full reversal.”  Scherrer explained earlier in December that “the sun’s north pole has already changed sign, while the South Pole is racing to catch up.”  The impact of the process has been extremely far-reaching.  “The domain of the sun’s magnetic influence (also known as the ‘heliosphere’) extends billions of kilometers beyond Pluto. Changes to the field’s polarity ripple all the way out to the Voyager probes, on the doorstep of interstellar space,” Phillips explained.

NASA has released a visualization of how the switch occurs. Beginning in 1997 and ending in 2013, it shows the green (positive) polarity switching with the purple (negative) polarity.  Solar Cycle 24 has been viewed as quite unpredictable. First, it came late by about a year, with extremely low activity recorded throughout 2009. This prompted astronomers to shift a predicted 2012 peak to 2013. Scientists say the cycle is already among the weakest reported and if the trend continues, the Earth might see another Little Ice Age.

Artist’s conception of the heliospheric current sheet, which becomes more wavy when the sun’s magnetic field flips

by Dr. Tony Phillips of NASA / Dec. 6, 2013

Something big is about to happen on the sun. According to measurements from NASA-supported observatories, the sun’s vast magnetic field is about to flip. “It looks like we’re no more than three to four months away from a complete field reversal,” said solar physicist Todd Hoeksema of Stanford University. “This change will have ripple effects throughout the solar system.”

The sun’s magnetic field changes polarity approximately every 11 years. It happens at the peak of each solar cycle as the sun’s inner magnetic dynamo re-organizes itself. The coming reversal will mark the midpoint of Solar Cycle 24. Half of “solar max” will be behind us, with half yet to come. Hoeksema is the director of Stanford’s Wilcox Solar Observatory, one of the few observatories in the world that monitors the sun’s polar magnetic fields.

The poles are a herald of change. Just as Earth scientists watch our planet’s polar regions for signs of climate change, solar physicists do the same thing for the sun. Magnetograms at Wilcox have been tracking the sun’s polar magnetism since 1976, and they have recorded three grand reversals—with a fourth in the offing. Solar physicist Phil Scherrer, also at Stanford, describes what happens: “The sun’s polar magnetic fields weaken, go to zero and then emerge again with the opposite polarity. This is a regular part of the solar cycle.”

A reversal of the sun’s magnetic field is, literally, a big event. The domain of the sun’s magnetic influence (also known as the “heliosphere”) extends billions of kilometers beyond Pluto. Changes to the field’s polarity ripple all the way out to the Voyager probes, on the doorstep of interstellar space. When solar physicists talk about solar field reversals, their conversation often centers on the “current sheet.”

The current sheet is a sprawling surface jutting outward from the sun’s equator where the sun’s slowly rotating magnetic field induces an electrical current. The current itself is small, only one ten-billionth of an amp per square meter (0.0000000001 amps/m2), but there’s a lot of it: the amperage flows through a region 10,000 km thick and billions of kilometers wide. Electrically speaking, the entire heliosphere is organized around this enormous sheet. During field reversals, the current sheet becomes very wavy. Scherrer likens the undulations to the seams on a baseball. As Earth orbits the sun, we dip in and out of the current sheet. Transitions from one side to another can stir up stormy space weather around our planet.

Cosmic rays are also affected. These are high-energy particles accelerated to nearly light speed by supernova explosions and other violent events in the galaxy. Cosmic rays are a danger to astronauts and space probes, and some researchers say they might affect the cloudiness and climate of Earth. The current sheet acts as a barrier to cosmic rays, deflecting them as they attempt to penetrate the inner solar system. A wavy, crinkly sheet acts as a better shield against these energetic particles from deep space.

As the field reversal approaches, data from Wilcox show that the sun’s two hemispheres are out of synch. “The sun’s north pole has already changed sign, while the south pole is racing to catch up,” Scherrer said. “Soon, however, both poles will be reversed, and the second half of solar max will be underway.” When that happens, Hoeksema and Scherrer will share the news with their colleagues and the public.

Computer simulation shows the sun’s “heartbeat” is magnetic
by Bob Yirka / Apr 05, 2013

A research team made up of Paul Charbonneau, a physicist with the University of Montreal and Piotr Smolarkiewicz, a weather scientist with the European Centre for Medium-Range Weather Forecasts in the U.K., has created a new kind of computer simulation of the sun’s energy flow. In their Perspective article published in the journal Science, the two describe the solar engine deep within the sun as its “heartbeat” and suggest that it underlies virtually all solar activity.

To gain a better understanding of how the sun works, the two researchers created a simulation that models the sun’s entire magnetic field activity—no small feat. They ran their simulation on University of Montreal supercomputers which are connected to a larger network across the city. In so doing, they observed that though the sun as a whole experiences an 11 year cycle of solar polar reversals (as noted here on Earth by the periodic nature of observable sun spot activity), zonal magnetic field bands undergo a polarity reversal on average every 40 years.

NASA finds frothy magnetic bubbles at the edge of our solar system

Scientists have for years been trying to model the sun, but thus far attempts to do so have been lacking. The problem is that there is so much going on and the sun is so huge—to simulate it all requires more computing power than is available. At the root of all the simulations is turbulence, which is where a gas or fluid flows in a chaotic fashion. The new model shows that turbulence in the sun comes from within and flows outwardly, dissipating into ever smaller vortices, but it, like other simulations can only model this dissipation to a certain degree. At some point, the vortices are as small as just meters across and thus are too small to include in a model because there are just too many of them. The simulation built and run by Charbonneau and Smolarkiewicz goes as far as modern computers are able and shows the suns’ action as a dynamo—where the amplification of a magnetic field is self-sustained due to fluid motion action.

Studying the sun and how it works is not purely academic, of course, learning how to accurately predict solar flares—when they might occur and how large they might be, would be very useful as the world becomes more and more dependent on sensitive electronic instruments that can be adversely impacted by events on the sun.

Modeling the Solar Dynamo, Science 5 April 2013: Vol. 340 no. 6128 pp. 42-43 DOI: 10.1126/science.1235954

“The Sun’s magnetic field is the engine and energy channel underlying virtually all manifestations of solar activity. Its evolution takes place on a wide range of spatial and temporal scales, including a prominent 11-year cycle of successive polarity reversals over the entire star. This magnetic cycle in turn modulates the physical properties of the plasma flowing away from the Sun into interplanetary space, the frequency of all geoeffective eruptive phenomena (such as flares and coronal mass ejections), and the solar radiative flux over the full range of the electromagnetic spectrum—from x-rays through ultraviolet, visible, and infrared light, all the way down to radio frequencies (1). The Sun’s heartbeat is truly magnetic, and recent numerical simulations (2–5) are providing new insights into its mode of operation.”

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