Subject: mundane science Date: Tue, 20 May 2003 18:24:58 -0400 From: "Downs, Bill" Mundane Science Captain Bill Downs Nature Rages To Restore Calm June 22-28 is Lightning Awareness Week. Since we are having a lot of storms and tornados lately, I thought it would be a good idea to review the science and the safety. We all probably have a similar story. I was leaving work one day when I looked up. I saw the clouds rolling in and heard the thunder. For some reason, I decided to go back inside rather than continue to the bus stop. Within a few minutes, the hail started. As the hail got larger, the rain started. As the hail approached quarter sized, the rain was almost horizontal. When the storm finally let up, the ground was almost covered by hail and there was an inch or more of water against the building, leaking under the doors. Mother Nature is happiest when the atmosphere is stable. Next time you're in a cold room, do an experiment. The coldest temperature should be near the floor and the highest temperature near the ceiling. It may not be comfortable for you but it is what Mother Nature likes. When the atmosphere is "upside down", hot, humid air near the ground while the higher air is cool and dry, storms can occur. A tiny speck of dust rises through a cumulonimbus (mountain shaped) cloud. Moisture condenses on the speck until it is heavy enough to fall. Its' fall, along with millions of similar drops, brings cold air down with it and builds up an electric charge, released as lightning. We've all had it happen. You walk across a carpet and a spark jumps between your hand and the doorknob. Lightning is basically the same thing, except on Mother Nature's grander scale. The bottom of the cloud has a mostly negative charge and the top, mostly positive. Much of a storm's lightning remains within the cloud, leaping the gap between top and bottom. If an object on the ground, such as a building, or tree, or person, becomes positively charged, lightning can spark to the ground instead. If you count the number of seconds that pass between the lightning flash and the first sound of thunder, you can tell how far away the lightning was. Thunder travels at the speed of sound, about 1100 feet per second. If 5 seconds pass between the flash and the thunder, the lightning strike was just over a mile away (1100 fps * 5 sec3D 5500 feet (5280 feet3D 1 mile)). 10 seconds is about 2 miles. 2 seconds is less than a half-mile and you should be under cover by now. Besides lightning, thunderstorms can create havoc in other ways. Strong winds are a typical part of thunderstorms. Some systems can produce a microburst. A microburst is a violent downdraft that has very high winds, sometimes approaching 150 miles per hour, over a narrow front.=20 Slow-moving storms can produce large amounts of rain in a short period of time. The ground can only absorb a certain amount of moisture at a time. The rest runs off into the sewers, the streets, the creeks and streams. If the water levels are rising very fast, that is flash flooding. Flash floods can wash away roads and bridges. They can put a house under water before you can respond.=20 If that tiny speck of dust rises high enough and stays there long enough, it can freeze and fall as hail instead of rain. The longer it stays up, the larger it grows. A hailstorm at the Dallas airport in 1995, damaged so many planes that some airlines temporarily lost portions of their fleets while repairs were made. Thunderstorms can also produce tornadoes when the winds at ground level are moving at a different speed &/or direction from the winds aloft, causing the clouds to spin. The ground end of a tornado can travel in a straight line, zigzag, or even hop around. If the Weather Service issues a tornado warning, that means a tornado has been sighted in the area and it is time to head for the basement or an interior room. Forecasters may sound like they're "crying wolf" every time they forecast a "chance of thunderstorms" and nothing happens, but they're not. They are telling you that conditions exist which may cause a storm to be created. It is for your own safety that you should pay attention to conditions and the forecast. You may not have any more warning than a darkening sky as the storm approaches. Having respect for the thunderstorm can keep you and those you care about safe when the big clouds gather. How To Stay Safe Thunderstorms can arrive very suddenly. The only warning may be a darkening sky as the clouds approach. If you see tall, puffy cumulus clouds growing and it's rapidly getting darker, observe these safety measures: If you're near a house or other building: * Make sure everyone is accounted for. * Secure outdoor furniture. * Go indoors. If the storm is severe, head for the basement or an interior room. * Keep away from objects that might conduct electricity (radiators, pipes, metal doors and frames). * Stay away from the windows. * Do not take a bath or shower during a storm. * Stay away from plug-in appliances. Use a battery-operated radio. * Stay off the phone. Use a cell phone. * Don't stand on the roof during a storm. If you're in the open (Half of all lightning casualties take place in the open, such as an athletic field or a golf course): * If you feel your hair start to stand on end or your skin tingle, or you hear crackling sounds, lightning may be about to strike. Bend over quickly, feet together, hands on your knees. Do not lie flat on the ground. You want to make yourself as small as possible and have as little contact with the ground as possible. * At the first sign of thunder, get inside a substantial building or a vehicle with a metal roof and sides. If you're swimming: * Get out of the water at the first sign of lightning or thunder. Find indoor shelter or get into a car. Stay out of the water for at least 30 minutes without thunder. * Stay away from metal fences or poles. If someone is struck: * Seek medical help at once. Heart attack is the usual cause of lightning fatalities. Suggestion: * An electronic surge suppressor won't help if the lightning strike is close to the house but might if it is farther away. Get a good quality one (higher ratings are better) and use the telephone jacks to protect your modem. "When The Big Clouds Gather," David H. Levy, Parade Magazine, 5/18/03, pgs 4-5