How It Works: Science and Technology - Vol. 8

By Wendy Horobin | Go to book overview

Hurricane and Tornado

This farm in the United
States is threatened with
destruction by the rapidly
moving winds of a tornado.
In certain parts of the
world, such as central
areas of the United States,
tornadoes are common
and can cause large-scale
devastation.

Cyclones are violent circular storms with winds rotating about a calm center of low atmospheric pressure. When they occur in the tropics of the western Atlantic, they are referred to as hurricanes, in the western Pacific they are called typhoons, and if they occur on land they are called tornadoes.


Hurricanes

Near the center, hurricanes are characterized by wind speeds over 73 mph (117 km/h). We know they are spawned over the oceans in a band of latitudes between 5 and 20 degrees on either side of the equator. To grow, they must remain over a sea surface having a temperature of at least 80°F (26°C). They moderate and eventually die, either when they drift northward (in the Northern Hemisphere) over cooler seas or are cut off from their moisture supply by passing over extended areas of dry land. The center of a hurricane is called the eye. This area often experiences only light breezes or even complete calm. The surface pressure generated in the eye by the weight of air in the column above is similar to that found at a height of 3,000 ft. (900 m) in the area near the periphery of the storm.

Air attempts to rush toward the center of the hurricane and fill the void, but because of the rotation of Earth, such a flow is deflected and forms a spiral, which rotates counterclockwise in the Northern Hemisphere but clockwise south of the equator. This phenomenon, called the Coriolis effect, causes the hurricane to develop in a way similar to that of a spinning ice skater who increases his or her speed of rotation by pulling the arms in towards the body—in a hurricane, the inward spiraling air rotates faster and faster.

Peak velocities are reached in a narrow ring surrounding the low-pressure center, with a radial distance of about 20 miles (32 km). The converging air outside this ring, warmed and moistened by the broken sea over which it flows, is forced upward. Water vapor condenses in the ascending air, releasing its latent heat and forming massive cumulonimbus clouds, which in turn generate torrential rain. In the ring of maximum wind, the towering clouds merge into a wall encircling the eye, where cloudiness is minimal and rain is absent.

In its mature form, the hurricane is a selfsustaining heat engine in which the warm core is a result of the heating of the inflowing air by the

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How It Works: Science and Technology - Vol. 8
Table of contents

Table of contents

  • Title Page *
  • Contents *
  • Gold 1013
  • Governor 1017
  • Grass-Cutting Equipment 1018
  • Gravity 1020
  • Gun 1023
  • Gyrocompass 1028
  • Gyroscope 1030
  • Hair Treatment 1032
  • Halogen 1034
  • Hang Glider 1037
  • Head-Up Display 1039
  • Hearing 1041
  • Heart 1045
  • Heart Pacemaker 1048
  • Heart Surgery 1049
  • Heat Engine 1053
  • Heat Exchanger 1054
  • Heating and Ventilation Systems 1056
  • Heat Pump 1063
  • Helicopter 1065
  • Hi-Fi Systems 1071
  • High-Speed Photography 1077
  • Holography 1080
  • Hormone 1084
  • Horticulture 1088
  • Hosiery and Knitwear Manufacture 1090
  • Hurricane and Tornado 1094
  • Hydraulics 1100
  • Hydrocarbon 1105
  • Hydrodynamics 1109
  • Hydroelectric Power 1112
  • Hydrofoil 1116
  • Hydrogen 1118
  • Hydroponics 1120
  • Hygrometer 1123
  • Ignition System, Automobile 1124
  • Image Intensifier 1128
  • Immunology 1132
  • Induction 1138
  • Inertia 1142
  • Information Technology 1147
  • Ink 1151
  • Index i
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