For the last few years the sun has been kicking back and relaxing. A lot. Although a huge solar flare recently made headlines, the surface of the sun has been quiet lately. Sunspots have been more scarce than they've been in the last 200 years. All solar activity is low. And it looks like it's going to stay that way for a while. The sun is likely in an 11-year cycle that will bottom out in 2013 or 2014. But why is the sun being so very cool lately?
Now two groups of scientists have announced theories that directly contradict each other.
Let's start with what they agree on. Both groups believe that this cooling is the work of the meridional flow. At the north side of the sun's equator, the hot plasma flows up towards the north pole. At the pole it sinks down into the interior of the sun and flows back to the equator. The same thing (in reverse) happens just south of the equator. This is the meridional flow.
Over at the Indian Institute of Science Education and Research, researchers postulate that a fast flow at the beginning of a solar cycle followed by a slow flow at the end leads to a weak polar magnetic field and generates a weak sun cycle. Meanwhile the Marshall Space Flight Center believes just the opposite. A slow flow followed by a fast one creates a weak field and a weak sun.
Both theories are hard to test, since there's only one sun, it's 93 million miles away, powered by nuclear explosions, and everyone on earth is using it. The contradiction shows the complexity of the problem. One thing both centers do agree on: the low in solar activity won't last forever. It's been helping the earth stay cool, despite increased greenhouse gases. When it stops, things may get very warm around here.
Image Credit: NASA