Everybody talks about the weather, but nobody does anything about it, Mark Twain is said to have remarked. Whether it rearranges your picnic plans or tears apart your home, weather has just two predictable traits: it happens to everyone, and it changes. The most extreme forms of weather entrance us because they show nature at its most destructive--and its most beautiful.
As dazzling as it is fleeting, lightning is a huge electric spark between regions of oppositely charged particles. The most familiar form of lightning is cloud-to-ground, in which a negative discharge from a cloud (called the leader) rushes downward. Just before the leader strikes the earth, an upward flow of positive charge (called the return stroke) arcs up to meet it. The return stroke is more than four times hotter than the surface of the sun. Lightning superheats the air around it, which causes the air to expand violently in pressure waves that we hear as thunder claps or rumbles. To figure out how many miles away a thunderstorm is, count the number of seconds between the flash of lightning and the sound of thunder, then divide by five.
Clouds are our best bet in predicting what the weather will do, and they are often spectacular to look at as well. Watching clouds is a time-honored tradition; gazing at the almost-predictable (but ultimately random) cloud patterns even helped physicists to develop the new science of chaos theory. Altitude, wind, and landscape all play a role in shaping clouds, from the feathery wisps (cirrus) to the puckered "mackerel" sky (altocumulus) to the anvil-shaped masses (cumulonimbus) that presage heavy weather.
Freakish and arbitrary, tornadoes are the most violent storms of all. They can demolish a barn and leave the cows inside it standing unharmed. They can hurl cars into trees, and they carry houses for a mile or more before gently setting them down. Tornadoes are violently rotating columns of air, with wind speeds estimated up to 280 miles per hour. Their funnels can be as wide as two miles across, and their lifespans range from several seconds to as many as seven hours. Eighty-seven percent of all tornadoes travel from southwest to northeast. America's Great Plains region is the most favorable environment on earth for the formation of tornadoes, with central Oklahoma enduring more tornadoes per acre than anywhere else.
Hurricanes are the largest storms on earth, with some as large as 600 miles in diameter. Born as tropical storms, hurricanes only form where the ocean temperature is at least 78 degrees and in areas above 10 degrees in latitude, where the earth's spin is strong enough to generate a rotating storm. Hurricanes may last as long as 30 days and travel several thousand miles before their force is spent. Surrounded by the churning mass of clouds, rain, and winds of up to 155 miles per hour is the hurricane's eye: an oasis of calm air where blue sky may be seen far above the storm. The eye sometimes teems with birds trying to escape the hurricane's fury. Although hurricanes do their worst damage to coastlines, they often trigger severe storms and flooding hundreds of miles inland.
With your new Severe Weather ScreenSaver you're free to contemplate the beauty and complexity of severe weather--without the perils of the real thing. Rain or shine, this collection of images will keep you in in touch with the natural phenomena that shape our world.
