extreme weather effects on earth
weather on earth
A cyclone is a rotating storm system centered around an area of low pressure. It forms as warm, moist air rises, causing a fall in pressure, which draws in more moist air from all directions. An effect known as the Coriolis force causes the air to spiral, counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.
Tropical cyclones In temperate regions, cyclones are often called depressions and are only rarely destructive. They are at their most intense in the tropics. They are called hurricanes in the North Atlantic, cyclones in the Indian Ocean, and typhoons in the western Pacific.
A tropical cyclone forms over the ocean in the presence of slack winds and surface temperatures of more than 79°F (26ºC) usually in late summer or early fall. It becomes a full cyclone when winds exceed 73 mph (118 kph), although sustained speeds can exceed 200 mph (320 kph). Combined with torrential rainfall, this can cause flooding and mudslides and bring down buildings. During their most vigorous phase, cyclones track west. They begin to die only once they make landfall and their supply of warm ocean water is cut off.
FORCE OF NATURE
Palm trees bend in intense winds as Hurricane Dennis hits the coast of Florida in July 2005, although the storm surge created more damage than the winds. Flat top The top of the storm may be as high as 9 miles (15 km) above sea level. Downpours The area beneath a cloudband is subjected to heavy rainfall, strong winds, and lightning. Cloudbands Spiralling around the eye are cloudbands that can extend for hundreds of kilometers from the cyclone center, gradually diminishing in height.
The intensity and scale of cyclones makes them the most destructive phenomena in Earth’s atmosphere.
Thunderstorms come in different shapes and sizes. Single-cell storms typically last 20–30 minutes and may produce heavy rainfall and hail. Larger multicell storms may generate weak tornadoes. The most severe thunderstorms are supercells, which are bigger and may produce violent tornadoes. Severe thunderstorms are classed as those with hailstones 1in (2.5cm) in diameter, winds of more than 56 mph (90 kph), or tornadoes. Lightning strikes As tiny water droplets and ice crystals in the cold tops of the clouds bump into each other to form bigger drops of rain and hailstones, these particles develop positive and negative electrical charges. It is this difference in charge (potential difference) between the particles that creates lightning, as a flow of electrons moves from the negatively charged particles to the positive. Lightning is extremely hot, and as it passes through air it causes the air to expand instantaneously.
This expansion creates a shockwave—the familiar rumble of thunder. Lightning zigzags between one part of the cloud and another, between the cloud and air, or between the cloud and the ground.
With a tight vortex of air spinning at up to 300 mph (480 kph), a grade F “twister” is the most terrifying sight in nature, capable of destroying almost anything in its path.
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To meet the definition of a tornado, the vortex must extend from the base of a cloud and be in contact with the ground. Types of tornadoes Tornadoes can happen anywhere, but most occur on the Great Plains of the U.S.
They occur in different shapes and sizes. Rope tornadoes have a narrow funnel, while wedge tornadoes have a wide diameter at the ground and are even broader at the cloud base. Tornadoes change color depending on the nature of the debris and dust that they pull into their violent vortex and may be near-white, brown, reddish, or nearly black.
Their severity is measured on the Fujita scale. An F-0 twister—the most common type—is capable of breaking branches from trees, while an F-5 one is able to carry cars 330 ft (100 m) through the air. Tornadogenesis The ideal situation for a tornado to form, a process known as tornadogenesis, is when a cold air mass converges with a warm, moist one, creating instability and towering cumulonimbus clouds.
Where there is also wind shear (a change in wind speed or direction with height), a slowly rotating supercell storm may develop. If an input of warm, rising air is in contact with the rapidly descending air of the storm’s rear flank downdraft, a narrow column of rapidly spinning air develops. The rotating air continues downward, forming a funnel below the cloud.
Air drawn into the funnel enters an area of much lower pressure, so it expands and cools, and moisture condenses as a result. The funnel becomes a tornado on touching the ground.
The biggest twister on record is the Tri-State Tornado of March 18, 1925, which was in contact with the ground for at least 219 miles (352km). It wreaked havoc across Missouri, Illinois, and Indiana, leaving 695 dead. Bangladesh has the highest annual death toll caused by tornadoes, averaging almost 200 each year.
Tornadoes Virtually impossible to predict accurately, tornadoes are the most capricious weather phenomena—and some of the most violent Bangladesh’s Daulatpur– Saturia tornado of April 26, 1989, killed 1,300 people.
Unlike in other storms, conditions are often calm and quiet during an ice storm. But in terms of loss of life, disruption to transportation and power networks, and general mayhem, a major ice storm can produce as much chaos as a tornado or hurricane.
The vital elements that cause this phenomenon are a combination of heavy rain falling from a wedge of warm air, an underlying area of supercold air, and freezing ground temperatures. When the rain hits the ground, or any subfreezing structure close to it, it freezes and forms a layer of ice known as glaze ice. As the rain persists, this glaze ice grows thicker. Collapse under pressure Glaze ice can be over 2 in (5 cm) thick. In 1961, a layer 8 in (20 cm) thick was measured in parts of Idaho. Since ice is 10 times as heavy as the equivalent thickness of wet snow, the effects are often dramatic. Apart from turning everything white, power lines, trees, and unstable buildings are brought down. Roads become impassable, and aircraft are grounded.
In January 1998, an ice storm hit a vast area of New England and southeast Canada—a region particularly susceptible to these events. At least 44 people died, with hundreds more injured. Some 80,000 miles (129,000km) of power cables collapsed, leaving four million people without power. Ice Storms Unique meteorological phenomena that produce spectacular beauty and destruction in equal measure.
INSIDE A HURRICANE
At the core of a hurricane, very low pressure makes the surrounding air and storm clouds spiral inward. The wind speeds up as the spiral tightens. A strong updraft around the calm eye of the storm builds the tallest clouds, which produce heavy rain. They are topped by high cirrus clouds that spill out in the opposite direction.
Hurricanes build up over tropical oceans with surface temperatures of 80°F (27°C) or more. They generally move west, driven by the tropical trade winds, until they hit land and veer off in a new direction. This satellite image shows Hurricane Irene approaching Florida in August 2011.
Hurricanes In the tropics, the intense heat evaporates vast quantities of ocean water. This builds up colossal cloud systems centered on a zone of very low air pressure. Air swirls into the low-pressure zone and sets the cloud mass spinning, creating a tropical revolving storm, or hurricane.