Monday, May 14, 2012

Solar, Space, and Geomagnetic Weather, Part 3

So what are the effects of coronal hole winds and Coronal Mass Ejections (CMEs)?

They can actually raise the temperature of the outer layers of the Earth's atmosphere (the thermosphere, aptly named) sufficient to cause it to expand. This affects us, because that increases drag on satellites and spacecraft, and can cause the orbits of satellites to decay and re-enter well before they were intended. This is really bad if it's something important, like a weather satellite during hurricane season. After all, if the people of Galveston had had weather satellites in 1900, the city could have been evacuated well before it got hit, because they would have known it was coming for days. If we DON'T have weather satellites because we've lost 'em to increased atmospheric drag, we might as well go back to those days, as far as weather prediction is concerned. Ditto communications satellites. Don't even mention GPS.

Disruption of the Earth's magnetic field can be a problem. It can disrupt radio communication (including cell phones) rather severely. It can damage satellites that remain in orbit. It can generate “induced current” in any lengthy conductor. Let's pause for a moment and talk about that.

Induced current is a way of using magnetic fields to generate electicity. Remember how I said, in part 1, that the “current” of plasma created by the Sun's rotation on its axis generated a magnetic field? The reverse is also true. A moving magnetic field can generate an electrical current in any conductor placed within the field. So the disruption of the geomagnetic field constitutes a “moving” magnetic field and will induce electrical currents in everything from power lines to pipes and conduits.

When these truly huge induced currents hit things like transformers and circuit breakers and power stations, they can quickly overload them. This, in turn, can (and has) cause(d) blackouts and brownouts, particularly in parts of the country/world where the power grid is not robust enough to handle significant surges.

Long pipelines, like the Alaskan Pipeline, can be affected as well. In fact corrosion is occurring at a higher rate than expected because its northerly location exposes it to such induced currents all the time (remember that the ends of a bar magnet's field are open).

And it causes the aurorae. Most of you reading this have heard of the Northern Lights, properly termed the Aurora Borealis, but there are also the Southern Lights, the Aurora Australis. These are actually ovals that circle the magnetic poles of Earth (and most other planets with magnetic fields, by the way. They've been photographed on Jupiter.) They are where the charged particles that have been caught up from the solar wind or CME into the geomagnetic field follow the field lines down into the atmosphere. The gas molecules become excited into a higher energy state, then discharge that extra energy as light. This is very similar – in fact, essentially the same – as a fluorescent light bulb, only natural and not contained. The colors are determined mostly by the main gas that is fluorescing. Carbon dioxide produces white light; nitrogen, pink or red; oxygen, green or blue. (It can also generate ozone.)

Now, having talked about all of this radiation that an increased solar wind and coronal mass ejections pump into our Earth's system in general, and the fact that there are more of these things when there are more sunspots, when do you think the Sun is sending out more energy, Solar Max, or Solar Min? Yup, despite the logic of sunspots being cooler, the Sun actually sends out more energy during Solar Max, when there are the most sunspots.

-Stephanie Osborn