When you look up at the daytime sky, the first thing you notice is that the Sun is warm, and bright. The Sun's radiation is what keeps the Earth habitable. What often gets overlooked is flux in the Sun's magnetic field, which also has an impact on the entire Solar system, and on the earth.
Recent studies from space borne observatories show that cosmic rays are nearly 20% higher than they've been at any other time during the Space Age when we've had direct observation of them, and this increase is likely caused by the reduction in the solar magnetic field, which has dropped in intensity to about 4 nanoTeslas from a typical field strength of 6-9 nanoTeslas.
Cosmic rays are typically protons or helium nuclei (with a few other heavier elements thrown in) accelerated to near light speed by stellar processes and supernova explosions. Because they carry a charge, they get deflected by the Sun's (and Earth's) magnetic fields. When the Sun goes on a solar minimum (which is usually indicated by a lack of sunspots), the magnetic field of the sun weakens; this magnetic field weakening means that cosmic ray counts go up.
Now, this is all well and good from a pure science perspective, but this is an Astronomy blog. How does the cosmic ray count affect amateur astronomy?
Well, for one, it means that all the satellite observatories we have in orbit are more likely to have problems. It doesn't take much in the way of a cosmic ray burst (or a solar storm warning) to cause a computer glitch and a loss of data. It also means we don't get to see the glorious sunspots on the face of the sun through appropriately filtered telescopes.
Somewhat more controversially, cosmic ray counts are also accused of causing global cooling. Without the Sun's magnetic field, more cosmic rays hit the Earth's atmosphere, and when they hit the atmosphere with sufficient energy, they appear to trigger clouds. Clouds at the right altitudes (about the same altitudes that cosmic rays interact at) reflect sunlight back into space, increasing the albedo (reflectiveness) of the Earth's atmosphere. More clouds mean cooler temperatures...and of course, more clouds means fewer nights where you can watch the stars.
We do know that the last two recorded 'cold snaps' (the Maunder Minimum and the Dalton Minimum) corresponded to cooler global temperatures, a higher percentage of days recorded in almanacs as being cloudy, and failed crops around the world. Whether or not we're heading into another one is open to debate, but recordings of the Earth's climate have shown a drop of 0.7 C since 1998, as the solar cycle has wound down. Since 2008, we've had several months on the sun with no sun spots, a weakening solar magnetic field, and rapid cooling that falls outside of anyone's climate models.
Does this mean that Global Warming is a myth? We do know that running uncontrolled experiments on the amount of CO2 the atmosphere can have on the only habitable planet we've got isn't terribly wise. However, it does seem that there are more factors for global temperature than show up in the commonly cited climate models. This of course needs to be taken in context with the very real facts we know about anthropogenic climate change.
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