write a short note on tornado.(50 words)
A tornado is a local storm of short duration (usually 510 minutes) formed of winds rotating at very high speeds, usually in a counter-clockwise direction (in the Northern Hemisphere). This storm is visible as a vortex—a whirlpool structure of winds rotating about a hollow cavity in which centrifugal forces produce a partial vacuum. As condensation occurs around the vortex, a pale cloud appears—the familiar and frightening tornado funnel. Funnels usually appear as an extension of the dark, heavy cumulonimbus clouds of thunderstorms, and stretch downward toward the ground. Some never reach the surface; others touch and rise again. Air surrounding the funnel is also part of the tornado vortex. As the storm moves along the ground, this outer ring of rotating winds becomes dark with dust and debris, which may eventually darken the entire funnel.
These small, severe storms form several thousand feet above Earth's surface, usually during warm, humid, unsettled weather, and usually in conjunction with a severe thunderstorm. Sometimes a series of two or more tornadoes is associated with a parent thunderstorm. As the thunderstorm moves, tornadoes may form at intervals along its path, travel for a few miles, then dissipate. The forward speed of tornadoes has been observed to range from almost no motion to 70 mph.
A tornado is a special kind of storm. It is a whirling wind, circling around a low pressure centre. A tornado reaches from a cloud to the ground as a vertical, funnel-shaped column of air. A violent tornado can travel wiwth the speed of about 300 km/hour. Its diameter can be as small as a metre and large as a kilometre and even more wider. A tornado creates extensive damage whre it touches the grround. Tornadoes occur very rarely in our country but they are very common in the USA and Canada.