It\u2019s coming back! Sunspot AR3664 gave us an amazing display of northern lights in mid-May and it\u2019s now rotating back into view. That means another great display if this sunspot continues to flare out. It\u2019s all part of solar maximum\u2014the peak of an 11-year cycle of solar active and quiet times. This cycle is the result of something inside the Sun\u2014the solar dynamo. A team of scientists suggests that this big generator lies not far beneath the solar surface. It creates a magnetic field and spurs flares and sunspots. <\/p>\n
<\/p>\n For a long time, solar physicists thought the magnetic dynamo was deep inside the Sun. That view may change thanks to work by researchers at MIT, the University of Edinburgh, the University of Colorado, Bates College, Northwestern University, and the University of California. The dynamo may be related to instabilities in what\u2019s called the \u201cnear-surface shear layer\u201d in the Sun\u2019s outermost regions. The activities in this layer result in the flares and sunspots we see more of as the Sun nears \u201csolar maximum\u201d. Flares are high-energy outbursts while sunspots are surface features with local magnetic fields. Sunspots are relatively cool regions on the solar surface and occur in 11-year cycles. <\/p>\n \u201cThe features we see when looking at the Sun, like the corona that many people saw during the recent solar eclipse, sunspots, and solar flares, are all associated with the sun\u2019s magnetic field,\u201d said MIT researcher Keaton Burns. \u201cWe show that isolated perturbations near the sun\u2019s surface, far from the deeper layers, can grow over time to potentially produce the magnetic structures we see.\u201d<\/p>\n To understand the magnitude of this finding, let\u2019s look at the structure of the Sun. We all know the Sun is a superheated ball of plasma. So, how does boiling plasma create a magnetic dynamo? \u201cOne of the basic ideas for how to start a dynamo is that you need a region where there\u2019s a lot of plasma moving past other plasma and that shearing motion converts kinetic energy into magnetic energy,\u201d Burns explained. \u201cPeople had thought that the Sun\u2019s magnetic field is created by the motions at the very bottom of the convection zone.\u201d<\/p>\n Of course, pinning down the exact location of the solar dynamo in the upper layers is difficult. Simulations can only go so far, and modeling the plasma flow throughout the entire Sun is a massive computing task. So, Burns and the team decided simulate a smaller piece of the Sun. They studied the stability of plasma flow near the solar surface. That required helioseismology data showing vibrations on the Sun\u2019s surface, which allowed them to determine the average flow of plasma in that region. \u201cIf you take a video of a drum and watch how it vibrates in slow motion, you can work out the drumhead\u2019s shape and stiffness from the vibrational modes,\u201d said Burns. \u201cSimilarly, we can use vibrations that we see on the solar surface to infer the average structure on the inside.\u201d<\/p>\n Think of the Sun as layered like an onion. Different plasma layers rush past each other as the Sun rotates, according to Burns. \u201cThen we ask: Are there perturbations, or tiny changes in the flow of plasma, that we could superimpose on top of this average structure, that might grow to cause the sun\u2019s magnetic field?\u201d<\/p>\n The team developed algorithms that they incorporated into a numerical framework called the Dedalus Project. They looked for self-reinforcing changes in the Sun\u2019s average surface flows. The algorithm discovered new patterns that could grow and result in realistic solar activity. Interestingly, those patterns also match the locations and timescales of sunspots. It turns out that certain changes in the flow of plasma at the very top of the Sun\u2019s surface layers generate magnetic structures. This isn\u2019t a new idea. Burns pointed out that the conditions there resembled the unstable plasma flows in accretion disks around black holes. Accretion disks are massive collections of gas and stellar dust that rotate in towards a black hole. They\u2019re driven by \u201cmagnetorotational instability,\u201d which generates turbulence in the flow and causes it to fall inward.<\/p>\n Burns and the team thought this phenomenon at a black hole might also be at work inside our Sun. They suggest that magnetorotational instability in the Sun\u2019s outermost layers could be the first step in generating its magnetic field. \u201cI think this result may be controversial,\u201d he said. \u201cMost of the community has been focused on finding dynamo action deep in the Sun. Now we\u2019re showing there\u2019s a different mechanism that seems to be a better match to observations.\u201d<\/p>\n Not only will the team\u2019s work help solar physicists understand the creation of the magnetic dynamo, but may give them insight into other solar phenomena. In particular, a dynamo in the upper 10 percent of the Sun may explain things like the Maunder Minimum. This was a period between 1645 to 1715 when there were very few sunspots. In some years, observers saw no sunspots at all. In other years, they observed fewer than 20. Astronomers did chart the 11-year sunspot cycle through that time, so the Sun wasn\u2019t entirely inactive.<\/p>\n If the Sun\u2019s magnetic dynamo operates in its outermost layers, the science of solar activity forecasting could get a big boost. Right now, it\u2019s difficult to tell when a flare might break out. Flares and coronal mass ejections like those that contributed to the May 10-11 geomagnetic storm can damage satellites and telecommunications systems here on Earth. In addition, power grids and other technology are at risk. In the long run, however, gaining new understanding of the Sun\u2019s dynamo is a big deal.<\/p>\n \u201cWe know the dynamo acts like a giant clock with many complex interacting parts,\u201d says co-author Geoffrey Vasil, a researcher at the University of Edinburgh. \u201cBut we don\u2019t know many of the pieces or how they fit together. This new idea of how the solar dynamo starts is essential to understanding and predicting it.\u201d<\/p>\n The Origin of the Sun\u2019s Magnetic Field Could Lie Close to Its SurfaceHow is the Sun\u2019s Magnetic Field Connected to Activity?<\/h3>\n
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Computing an Answer<\/h3>\n
Implications of the New Model<\/h3>\n
For More Information<\/h4>\n
The Solar Dynamo Begins Near the Surface<\/p>\nLike this:<\/h3>\n