Journey in Catastrophes: Three Forms of Violent Storms I. Winds

Journey in Catastrophes: Three Forms of Violent Storms
    Good morning. Today’s lecture will continue our journey in catastrophes. In this session, we are going to have a brief look at three forms of violent storms: tornadoes, waterspouts and hurricanes.
    As we know, sometimes winds move in violent storms which do a great deal of damage and are so strong that they are terrifying. These storms happen when a mass of hot air meets a mass of cold air. Winds are measured by the speed at which they travel. They are called gales when they are strong enough to uproot trees and blow down chimneys, and at sea to whip up high waves with long crests that curl over and break in great patches of foam.
    Thunderstorms happen when hot, damp air rises from the ground and meets cold air. As it mixes with colder air, there are very violent up currents and down currents and swirling eddies of air, and great clouds foam. The lightning flashes when accompanying thunderstorms are enormous sparks caused by electric changes in the air. They have such great heat that the air they touch expands violently, making the sound we call thunder.
    Gales and thunderstorms happen all over the world. Tornadoes, waterspouts and hurricanes happen only in certain areas.
    Tornadoes happen in the tropics over land, especially over the southern states of USA and also over southern-eastern Australia and north-west India. A tornado is a very violent wind-storm, in which the air whirls rapidly upward in a grayish funnel-shaped cloud, with its tip near the ground. It twists and sways in the sky like a diving thing and moves in a straight line over the countryside at about 6 to 30 miles per hour. No one knows exactly what starts a tornado, but it certainly happens when extremely hot, moist air meets cold, dry air. When two kinds of air try to pass each other, they get locked together, and the hot air spirals upward more and more quickly until it may be whirling round at between 400 and 500 meters per hour. Tornado season is generally March through August, although tornadoes can occur at any time of year. They tend to occur in the afternoons and evenings: over 80 percent of all tornadoes strike between noon and midnight. Tornadoes do a vast amount of damage, even though they seldom last for more than an hour or two. The speed of the whirling air makes quite small things such as grains of sand into dangerous weapons. Once in America a corn cob picked up by a tornado was shot through a horse’s skull and killed the horse. The hot air spiraling upward sucks everything in its path, rather as a vacuum cleaner does. Tornadoes have been known to tear steel bridges from their foundations, to uproot large trees, and to lift trains off their lines. People and animals have been lifted and carried some distances; a horse, for example, was once picked up, carried 2 miles, and put down again unhurt.
    A waterspout is a tornado that happens over sea. The whirling air sucks up water, and the waterspout moves along with a hissing, roaring, crashing noise. Sometimes tiny fishes are caught up, and their scales make the whirling column sparkle. When a waterspout passes from sea to land it becomes a tornado.
    Hurricanes are even more terrible than tornadoes. Nowhere are they more terrible and more frequent than in the West India, and the name "hurricane" comes from the name of the West Indian god of storms, Hunraken. They are called tropical cyclones in India, typhoons in China and Japan, and willy-willies in northern Australia. Hurricanes begin over tropical oceans in late summer. August and September are peak months during the hurricane season that lasts from June 1 through November 30. Hot, moist air rises as if in a chimney, perhaps over a tropical islet. It gets pulled by the turning of the Earth into a whirling movement, faster and faster until it is like an enormous thick gramophone record of air whirling madly round as it moves across the sea at between 12 and 24 miles per hour. Hurricane winds blow in a large spiral around a relative calm center known as the "eye". The "eye" is generally 20 to 30 miles wide, and the storm may extend outward 400 miles. As a hurricane approaches, the skies will begin to darken and winds will grow in strength. As a hurricane nears land, it can bring torrential rains, high winds, and storm surges. Many hurricanes never reach land but die out over the tropical oceans, having perhaps moved as much as 1800 miles during their life of 9 to 25 days. Those that reach land die swiftly, for they need the heat and moisture of ocean air. But before dying they cause terrible destruction. They flatten trees and buildings, flood everything with the torrential rain they bring with them, and sometimes create enormous waves which sweep inland over sea walls and harbors. In a terrible typhoon in Japan in 1934, over 4000 people were killed and ships were lifted over sea walls into the streets. Hurricanes are given names, always feminine ones such as Besty or Alice. The first of the season is given a name beginning with A, the second with B, and so on. Hurricanes in some years have reached Janey or Katy.
    OK, that is all for this session. Thank you!