Windswept_ The Story of Wind and Weather - Marq de Villiers [33]
I
Sometimes you really can see the wind. Directly, not just by watching trees sway or ripples skitter across open water. Last year we had a two-day blizzard that dropped almost a yard of snow in gusty 50-mile-an-hour winds. At its height, you could stare out the window and watch the white wind dipping and swirling through the trees, heaping the snow up in great sculptured drifts, darting around the corner of the house. We had often wondered why the greatest damage in wind storms seemed to be done to a row of rhododendrons on the lee side of the house, and suddenly we could see the reason for ourselves—the wind dashed itself at the corner of the building and split, some of it going straight up and tugging at the eaves but the rest swirling around the corner, where it was squeezed between the house and a cut in the bank, suddenly accelerating just before it passed the rhodos, tearing at their leaves. I had already "seen" the wind in the violent dust storms of my boyhood in South Africa, where the prevailing color was not white but a brutal violet, and later in Saharan sandstorms, where the wind blows a gritty ochre and dun, and of course tornadoes are lethally visible. But these are crude views, made visible only by wind's awful force. And so when I read a lyrical passage in Sebastian Smith's sailing memoir, Southern Winds, I found myself nodding in agreement: "Sometimes, staring into the sky, I tried to imagine what it would be like to see the wind. As if there might be special glasses to understand [the wind's] secrets—the paths used to reach seemingly impossible places, the mystery of opposing airs and the drama of the katabatic wind. In simulations these can be created but to ordinary men they remain as inscrutable as any god . . . Imagine standing on deck and being able to watch jet streams swoop through the summer skies. Or the slow turning wheel of low-pressure systems. Or the avalanche of a squall."2 Just so. How wonderful to be able to watch the wind's intricate dance across the planetary surface and high into the troposphere, to see how great air masses move and collide and meld and wrestle, how little zephyrs tickle the fine hairs on the forearm, how the breezes tease their way through trees and over rocks and up hillsides. Sometimes airplanes hit an air pocket—which is really vertical-shear wind plunging violently downward through pressure differentials in the surrounding air. Wouldn't pilots, and their passengers, love to see that wind before they hit it?
We can understand wind—we understand it now almost to the molecular level—but it would be much more agreeable, and infinitely more useful, to be able to see it.
Find starts, of course, as with so much else on our planet, with the sun.
Deep inside the seething cauldron of the sun, thousands of miles beneath the corona, or what passes for its surface, is a constant cascading series of hydrogen fusion reactions. Every nanosecond millions of hydrogen atoms crash together, and for every four that destroy themselves in this furious suicide, one helium atom is created. Since four hydrogen atoms weigh slightly less than one helium atom, a fraction of the mass is lost each time, and this shortfall—pace Einstein—is released as pure energy.3 So much energy, indeed, that the temperature of the sun is maintained at a fairly steady 15 million degrees Celsius. Some of that energy is radiated into space. A tiny fraction, about two billionths, reaches the earth.4 This might not seem a lot, but the sun is so massive relative to Earth that the solar radiation reaching us is around 175 trillion kilowatt hours of energy every hour.5 Somewhere between 1 and 2 percent of this energy input is converted into wind, about fifty to one hundred times more than all the energy converted into biomass by all living things on Earth.
These trillions of watts of solar energy strike the earth directly at the equator and more obliquely closer to the