科普类.doc

1 一、科普知识类 A tornado ( 龙卷风) isa violently turning column of air that is in contact with both the surface of the earth and a cumulonimbus cloud( 积雨云). e in many shapes and sizes, but they are typically in the form ofa visible c ondensation funnel( 漏斗). Most tornadoes have wind speeds less than 177 km/h, are about 76 meters across, and travel several kilometers before disappearing. The most extreme tornadoes can reach wind speeds of more than 483 km/h, stretch more than km across, and stay on the ground for more than 100 km. Various types of tornadoes include the landspout, multiple vortex tornado, and water - spout. Waterspouts are characterized bya spiraling( 螺旋式的上升) funnel - shaped wind current, connecting toa large cum ulonimbus cloud. They are generally classified as tornadoes that develop over bodies of water, but there is disagreement over whether to classify them as true tornadoes. These spiraling columns of air frequently develop in tropical areas close to the equat or, and are mon at high latitudes. Other tornado - like phenomena that exist in nature include the gustnado, dust devil, fire whirls, and steam devil; down - bursts are frequently confused with tornadoes, though their action is dissimilar. Tornadoes ha ve been observed on every continent except Antarctica. However, the vast majority of tornadoes occur in the Tornado Alley region of the United States, altho