龍捲風 的影響 the impacts of tornado!!!!! (10分!!!!!!)緊急!!!!!

This article is about the weather phenomenon. For other uses, see Tornado (disambiguation).

A tornado in central Oklahoma. The tornado itself is the thin tube reaching from the cloud to the ground. The lower half of this tornado is surrounded by a dust cloud, kicked up by the tornado's strong winds at the surface.A tornado is a violently rotating column of air which is in contact with both a cumulonimbus (or, in rare cases, cumulus) cloud base and the surface of the earth. Tornadoes can come in many shapes, but are typically in the form of a visible condensation funnel, with the narrow end touching the earth. Often, a cloud of debris encircles the lower portion of the funnel.

Most tornadoes have winds of 110 mph (175 km/h) or less, are approximately 250 feet (75 meters) across, and travel a few miles (several kilometers) before dissipating. However, some tornadoes can have winds of more than 300 mph (480 km/h), be more than a mile (1.6 km) across, and stay on the ground for dozens of miles (more than 100 kilometers).[1][2][3]

Tornadoes have been observed on every continent except Antarctica; however, most of the world's tornadoes occur in the United States.[4] Other areas which commonly experience tornadoes include New Zealand, western and southeastern Australia, south-central Canada, northwestern and central Europe, Italy, south-central and eastern Asia, east-central South America, and Southern Africa.[5]

The Fujita scale and the Enhanced Fujita Scale rate tornadoes by damage caused. The Enhanced Fujita Scale was an upgrade to the older Fujita scale, with better wind estimates and better damage descriptions, but was designed so that a tornado rated on the Fujita scale would receive the same numerical rating. An EF0 tornado will likely damage trees but not structures, whereas an EF5 tornado can rip buildings off their foundations and even deform large skyscrapers. The similar TORRO scale ranges from a T0 for extremely weak tornadoes to T11 for the most powerful known tornadoes.

Tornadoes vary in intensity regardless of shape, size, and location, though strong tornadoes are typically larger than weak tornadoes.

In the United States, EF0 and EF1 (T0 through T3) tornadoes account for 80% of all tornadoes. The rate of occurrence drops off quickly with increasing strength—violent tornadoes (stronger than EF4, T8), account for less than 1% of all tornado reports.[23] Outside of the United States and areas in south-central Asia, significant and violent tornadoes are extremely rare.

Tornadoes can leave a wide swath of devastation in their paths. Weak tornadoes typically break trees, cause damage to houses, and may knock over barns . Strong tornadoes are capable of demolishing houses from their foundations, leaving only scattered debris in the vicinity . Urban tornadoes can leave shattered glass from windows in storefronts and office buildings, along with extensive structural damage to large buildings, such as schools, shopping centers, and warehouses, in their wake.

The extent of damage depends not only on wind speed, but also on the mass and surface area of the object being struck. Objects with an extensive surface area are particularly subject to damage when hit head on by tornadic winds. Even a massive locomotive can be toppled, and automobiles can easily be picked up and battered. Mobile homes are no match for a tornado.

Secondary impacts of tornado damage result from damage to infrastructure. Downed power and communications transmission lines, coupled with disruptions to surface transportation, create difficulties in reporting and responding to emergencies.

Casualties are common. Fortunately, over 90 percent of tornado casualties are injuries. Casualties are most frequently associated with the collapse of buildings, being struck by flying objects, or trying to escape the tornado in a car. A compilation of tornado-related fatalities nationwide from 1985 through 1997 revealed that 38 percent of all fatalities occurred in mobile homes, 27 percent in permanent houses, and 11 percent in automobiles.