“Kenneth Chang in the New York Times reports that some observations seem inconsistent with the solar magnetic field–cosmic ray–cloud formation hypothesis. He wrote (CCNet 113/2009 — 21 July 2009, item 3):
Terry Sloan, a cosmic ray expert at the University of Lancaster in England, said if the idea were true, one would expect the cloud-generation effect to be greatest in the polar regions where the Earth’s magnetic field tends to funnel cosmic rays.
“You’d expect clouds to be modulated in the same way,” Dr. Sloan said. “We can’t find any such behavior.” Still, “I would think there could well be some effect,” he said, but he thought the effect was probably small. Dr. Sloan’s findings indicate that the cosmic rays could at most account for 20 percent of the warming of recent years. [sic — he clearly means the *reduction* in cosmic ray influx to the Earth in recent decades of the more active Sun — SA]
I am skeptical about Dr Sloan’s claim. The reason is as follows.
A few years ago I read a suggestion that an interstellar space probe might be able to do a flyby of the star Sirius, and use its gravity to redirect itself to a subsequent flyby of Procyon, in the same way that Pioneer, Voyager and other probes have used the gravity of Jupiter to redirect themselves to Saturn and beyond. I have a formula for the change in direction caused by a flyby of a massive body, so I was able to check this idea numerically.
It turned out that if the interstellar probe was travelling at a speed that was a significant fraction of the speed of light, say 0.1c — which it would have to if it was to reach Sirius in only a few decades flight time — then the deflection of its trajectory even on a flyby which grazed the star’s atmosphere was only in the region of one degree, totally insufficient to redirect it to Procyon.
The lesson was that the gravitational fields of planets and even stars (Sirius is more massive than our Sun) are almost imperceptible to a vehicle if it is travelling at such a high speed.
Cosmic ray particles come into the Solar System at a significant fraction of the speed of light. I would therefore expect them to be largely immune to our local gravitational and magnetic fields. I would not expect Earth’s magnetic field to funnel them towards the poles, as it does with the lower-energy solar particle flux. (Presumably someone has already checked this numerically?)
It would seem that Svensmark’s cosmic ray–cloud formation hypothesis depends on the difference in strength between the Sun’s and the Earth’s magnetic fields: the Sun being strong enough to modulate the cosmic ray flux in the inner Solar System over its longer-term cycles of activity, while the Earth is too weak to redistribute incoming particles geographically during their last second or so of flight before hitting the atmosphere.
23 July 2009
Stephen Ashworth, Oxford, U.K.
http://www.astronist.demon.co.uk/ ” CCNet today