Observations of unusual behavior on the sun’s surface intrigued astronomers this summer as our nearest star experienced one of the weakest solar maximums on modern record.
USC physics and astronomy professor Varsha Kulkarni weighed in on the causes of the phenomenon and the ways it could impact our planet.
“The Sun is not a completely predictable machine, and it does go through some surprises once in a while,” Kulkarni said.
The Sun’s magnetic activity goes through a roughly predictable eleven-year cycle that affects the number of sunspots visible on the star’s surface. Once every cycle, there is a solar maximum, during which there is a particularly high number of sunspots and solar flares.
The cycle is caused by changes in the Sun’s magnetic field. The star’s hot gases consist of charged particles that generate magnetic fields as they move. Because the Sun rotates faster near its equator than at its poles, the magnetic field lines, which get dragged along with the ionized gas, become increasingly twisted with time, resulting in sunspots and solar flares. Every eleven years, the Sun’s magnetic field reverses during a solar maximum.
Despite the fact that our Sun is experiencing a solar maximum, The State reported that there were absolutely no sunspots on July 17th, and the rest of the summer has seen markedly low activity.
Kulkarni said that this solar maximum is certainly the weakest recorded since the Space Age produced technology enabling astronomers to make more precise observations. It has only been within the last fifty years, she said, that scientists have begun to understand the sunspot cycle and have had the tools to better observe sunspots.
So why is the current solar maximum so weak?
The answer has to do with the changing of magnetic fields. When sunspots begin to diminish due to the declining intensity of the magnetic field, the field descends back into the interior region of the Sun. Normally, Kulkarni said, the passage through the inner region amplifies the decaying magnetic field.
However, the process of the fields reentering the interior may be occurring unusually fast, preventing the decaying fields from becoming sufficiently amplified again. Thus, Kulkarni explained, when the fields reach the Sun’s surface and sunspots reappear, the sunspots are not as strong as expected.
Though there are fairly solid theories about the solar dynamo and the sunspot cycle, the details about the cycle and the exact causes of its complex fluctuations are still not fully understood.
“This is an extremely complex subject … it is definitely a very active area of research even now,” Kulkarni said.
Will the fluctuations affect us?
While the low levels of solar activity will not noticeably change the visible brightness of the Sun, the solar cycle does affect the ultraviolet and x-ray output of the star. Astronomers are continuing to research solar activity’s effects on the Earth’s climate.
Astronomers predict that solar activity will increase over the course of the next year because this solar maximum is expected to fade out around 2015. During fade-outs, there is a heightened risk of solar flares affecting the earth.
“If the solar flare is prominent enough, then you’ll get disruption of communication satellites. Also, equipment on spacecraft can be endangered because of radiation damage,” Kulkarni said. “On the surface of the earth, you can see heightened auroras. You may see beautiful displays that are visible even to more southern latitudes without going up to, say, northern Canada.”
A few years ago, Kulkarni said, people as far south as Texas reported seeing the Aurora Borealis, also called the Northern Lights.
However, in less obvious ways, Kulkarni said, solar activity is always affecting us.
“We all know very well that it’s our basic energy source. So in that sense, of course, it’s been affecting us for a long time. But the solar magnetic activity also affects us constantly,” Kulkarni said. “It’s kind of sobering to think that the sun’s activity is intimately related to what goes on on the earth. Solar flares and auroras and so on are a nice reminder to us how our lives are intertwined with what happens on a star that is, compared to our earthly scale, very far away.”