Windswept_ The Story of Wind and Weather - Marq de Villiers [45]
Evidence is also accumulating that indicates the ocean's currents and hurricanes act together, in a feedback loop. The direction and speed of the conveyor belt can affect hurricane frequency, but the size and frequency of the storms can also push the Gulf Stream faster and farther. It was once thought that the prevailing winds alone, acting with our old friend the Coriolis force, caused the ocean's currents; it now seems that hurricanes have their part to play too. Kerry Emanuel, an atmospheric researcher at MIT, said in 2004 that the theory he had learned earlier in his career of how hurricanes began and sustained themselves was wrong. "It was always felt they were freak storms that didn't have much to do with climate in general . . . but we've come to different conclusions. Really, they are very integral to the climate system." His theory is that because hurricanes churn up the top 600 feet or so of the oceans, they lead ultimately to the circulation of all the world's oceans, which directly affects winds and storms, which in turn affect climate.25
This is the cheerful side of typhoons and hurricanes: Typhoons (from the Chinese ta, "great," and feng, "wind")26 and hurricanes (from Hunraken, the Mayan storm god)27 may be disruptive to a species that likes to build big-windowed homes by the sea, but within the complicated and coupled hydrographic-atmospheric system, they are nonetheless important agents of planetary self-government, redistributing air, moisture, and heat both vertically and latitudinally, scrubbing the air of accumulated pollutants, and accelerating the movement of the great ocean currents that keep our planet stable. A mature hurricane can export more than three and a half billion tons of air every hour, contributing greatly to redistribution of the troposphere, and can transport a billion tons of water over several degrees of latitude. They help make Earth work.
I should have thought of this when I was tracking Ivan. I mean to keep it in mind in the hurricane seasons to come. I just don't want a hurricane to drop any of that billion tons of water on me.
V
So much for climate cycles, the first of the three complicating factors in weather analysis. The second of these is the apparently irresistible need of flowing air (and liquids too) to form into vortexes.
By definition, a vortex is a rotation around a common center, often with a slow radial inflow or outflow superposed on the circular flow. As the air converges on the center, it begins to rotate faster and faster. "The process is surprisingly similar to an ice-skater's spin that accelerates as the skater's outstretched arms are drawn closer to the body"28
It's easiest to see in water—a whirlpool is a liquid vortex. Watch any stream that contains obstructions—a large rock, say—and you'll see a vortex, usually just upstream. I once watched a large log caught in just such an eddy, in a fast flowing river in British Columbia; it circled lazily in the eddy for more than three hours before its tip caught in the surrounding flow and it was dragged clear and went hurtling downstream (well, I had nothing better to do that day).
Vortexes occur throughout the universe, not just on our rotating little planet. Spiral galaxies are themselves versions of a vortex, caused by a combination of velocity and gravity. In our solar system, Jupiter's giant red spot, which is thought to be a long-lived vortex, is visible even to a small telescope. On Earth, cyclones are vortexes, and thus hurricanes and typhoons as well as tornadoes. Fire-caused whirlwinds are a hazard to firefighters. Dresden and Hamburg were both largely destroyed