The past few months have seen a spate of solar flares – bringing spectacular views of the northern lights as far south as Seattle – along with media speculation that the electrical activity could disrupt power grids, satellites or ground airplanes.
John Sahr , a UW professor of electrical engineering who studies the upper atmosphere, is the regional go-to guy for such questions. We found some time in Sahr’s busy schedule (he’s also the UW’s associate dean of undergraduate academic affairs and a part-time zombie hunter ) to get his read on the space weather forecast.
Q: Can you describe what we’ve been seeing in the last few months?
Well, let’s start with the sun. The sun has an 11-year cycle of times when it’s more busy and less busy, more stormy and less stormy. For the past five years the sun has been pretty quiet. We’re now rising up into the next solar maximum, which will last for about five years.
When the sun is stormy, there are more solar flares and more of what are called coronal mass ejections , which are basically just big puffs of electrically charged gas that burst out of the sun.
When this solar wind is gusty, it rattles the magnetic field around the Earth. That drives electric currents up and down along the Earth’s magnetic field lines. When those currents run into the Earth’s upper atmosphere, at altitudes of about 60 to maybe two- or three-hundred miles, they collide with the ionosphere and release energy in the form of light, causing the visual displays that we know of as the aurora.
Q: Why do we see these dramatic arcing displays?
The solar wind is a pretty good conductor, so it stretches the Earth’s magnetic field downwind, and it wiggles and moves. To know what’s happening during a solar storm, go over to the UW’s Red Square and look at the flagpole. When there’s a big stiff wind you hear it snapping and popping. That mechanical energy is the source, ultimately, for the northern lights. The Earth acts like a flagpole and the magnetosphere drapes past it, like the flag around the flagpole.
The lines of the Earth’s magnetic field act like wires, and it’s easy for the charged particles to move along the lines of the magnetic field. When people see the curtain effect of the aurora, what they’re seeing is light emitted from currents that flow along the Earth’s magnetic field. You actually can see the Earth’s magnetic field with your eye.
Q: Can we see predict solar activity and northern lights?
We can, to some extent. If you look at the sun through a telescope, the part of the sun that’s right in the center is roughly the part that’s throwing gas at you. If there’s a solar flare or sunspot that’s more out toward the edge of the sun, we’ll see that it happened, but the gas won’t hit the Earth.
When there’s a solar flare, the light gets here in eight minutes, but the coronal mass ejection gets here typically about two or two-and-a-half days later.
The other predictability has to do with the fact that the sun rotates every 30 days or so. So if you got hit with a bunch of solar wind from a particular sunspot, if the sunspot’s still there when the sun has rotated around, there’s a greater likelihood that we’ll get a burst of solar wind a month later.
And then, finally, there’s the 11-year cycle. We’re not surprised that we’re getting more magnetic storms now than we were for the past four or five years.
Q: Reporters often ask you to talk about solar activity. What do you think about the public’s reaction to solar storms?
Well, it comes up that there’s a solar storm, and sooner or later I’ll get the phone calls. And there’s always this hype about: "Whoa, it’s a really big magnetic storm, and what’s that gonna do?" And the answer is: "Well, people probably won’t notice."
It used to be a more significant effect on the power grid, because the currents that flow in the upper atmosphere can disturb the power system by driving big currents through the transformers along transmission lines. But the power companies know how to modify their system so that it’s much more robust to those great big surges.
Airlines that are flying over the poles will change their routes to be more southerly to reduce the energetic particle exposure, for the crews and passengers. By and large, we actually know how to respond to these things very well.
Probably the most significant impact of really big solar flares is the exposure of satellites. Satellites have to be designed with X-ray exposure in mind. One way is to have the satellites be within the Earth’s magnetosphere, but there are some that manage to be outside the Earth’s magnetosphere. One of the things that makes GPS a relatively reliable technology is that everybody wants it so badly, and there are now three or four different GPS-like systems. There’s the U.S. GPS one, there’s the Russian GLONASS, there’s a European system. These systems work about the same, and they’re constantly launching new satellites. They actually park spare satellites in orbit just to make sure the service keeps working. So I think [satellite] is something people can safely rely upon.
A little longer point of view, it’s important to remember that when we have people in orbit, these magnetic storms are really providing extra energetic particles and more X-ray exposure. As we begin to think about doing things like traveling to Mars, one of the things for people to remember is that those spacecraft will probably have to travel during a sunspot minimum, just to keep the radiation exposure of the astronauts to a minimum.
Q: What can we expect to see over the next few months?
We expect the actual peak in the sunspot cycle to be somewhere between about a year and two years from now. So what we’ve been seeing for the past several days or weeks will be typical for the next three or four years. The prediction is that this sunspot cycle will actually be somewhat less intense than the last one, which peaked in 2000 and was very active all the way through 2004.
This particular sunspot cycle is interesting because the depth of the minimum was remarkably deep, and the time since the last solar max is closer to 14 years, so this has been a bit of an unusual solar cycle.
Q: Where do you recommend going in Seattle to see the northern lights?