Life as an Extreme Sport

Magnetic Precipitation Tipping Point

How cool; magnets, rain and tipping points. It’s sounds like your basic power law, but basically it sounds like you can understand rain patterns by studying magnets!

Ole Peters, a 27-year-old physicist with expertise in “critical phenomena” and “self organized criticality” — which he acknowledges is “a bit of a rogue field” — doesn’t sound the least bit crazy.

In the June issue of the respected journal Nature Physics, he and J. David Neelin, UCLA professor of atmospheric and oceanic sciences, report that the onset of intense tropical rain and magnetism share the same underlying physics.

“We studied properties of that relationship that are also observed in equivalent quantities for systems with ‘continuous-phase transitions’ like magnets,” said Peters, a research scientist with UCLA’s Institute of Geophysics and Planetary Physics and a visiting scientist at the Santa Fe Institute.

“The atmosphere has a tendency to move to a critical point in water vapor where the likelihood of rain dramatically increases. The system reaches a point where it’s just about to rain; it’s highly susceptible. Any additional water vapor can produce a large response.”

“Our study showed that absolutely everything we dreamed of finding was actually there,” Peters said. “The predictions from critical phenomena showed up in the data. This is a huge step forward in self-organized criticality and critical phenomena. There really is a critical point. We observed the system in a whole range of different water vapors. This is the strongest evidence for any physical self-organized critical system to really have a critical point.”

How does a critical threshold point work?

Consider a pile of rice, Peters said. You can add a single grain of rice and measure its effect on the pile. After slowly adding rice grains, at some point you eventually trigger an avalanche; the release is very fast. A similar principle is behind the coin machines you can find in casinos, where it looks as if dropping in one or two quarters will create an avalanche of coins that will come crashing down for you. In fact, it is much more likely that it only looks like the system is at a critical point; you are more likely to lose your quarter.

Imagine that you add one raindrop into a cloud. Like the pile of rice, where adding a single grain can produce an avalanche or nothing at all, or like the coin machine, the one additional raindrop could trigger a huge downpour, but most of the time produces nothing. You can heat a magnet to a point where it loses its magnetization; it no longer has a north and south direction.

“When a magnet is near the critical temperature, a slight perturbation can cause it to switch north and south,” Peters said. “When the system reaches the critical point and is so susceptible, a slight change — one more grain of rice, one more coin — can produce a massive response of the system. This phenomenon can be studied using statistical mechanics and critical phenomena.”