Sunday, 1 May 2011

Report Text_Hurricanes


What is a Hurricane?

A hurricane is a huge tropical storm. Tremendous amounts of energy get sucked up into swirling winds. These giant wheels of wind can cause serious damage, especially if they reach land. The high tides and churned- up water in a hurricane cause damage too, and sometimes deaths.
This storm formed over the northwest Pacific Ocean, so it is called a typhoon.
These particular types of storms are called different names depending upon where they form. Storms that form over the Atlantic Ocean are called hurricanes. If they form over the northwest Pacific Ocean, they’re 
called typhoons. In the South Pacific and the Indian Oceans, they’re called cyclones. The scientific name is the same all over the world- tropical cyclone.

Hurricane Seasons

In the Atlantic Ocean, hurricane season begins June 1 and lasts until November 30. In the northeast Pacific, the season is a little longer. It goes from May 15 through November 30.  Most hurricanes occur in the hottest months—July through September. In the South Pacific, which is in the Southern Hemisphere, the season is the other half of the year - November through April.

How Do Hurricanes Form?

Hurricanes only form from warm ocean water. The water’s temperature must be at least 26°C. Warm air rises from the warming ocean. The air carries water vapor, the gas form of water. The water vapor cools as it rises. It turns back into a liquid. This condensation forms clouds, releasing heat energy into the air at the same time.
Hurricane Eloise
The large, dark clouds high above ground are photographed by a passenger on an airplane entering the center of Hurricane Eloise.
As evaporation and condensation continue, the air pressure at the surface of the ocean goes down. That lets more water vapor into the air. That vapor rises higher, where it condenses and releases still moreenergy. The cloud columns grow higher and larger. In this way, a hurricane is a storm that feeds itself. The more it grows, the more energy it releases. The more energy it releases, the more it grows.

How Much Energy?

Hurricane details
The illustrations above show different details of a hurricane including rain bands, eye wall and temperature.
Diagrams courtesy of University Corporation for Atmospheric Research and COMET
In a day, a hurricane can release an amount of energy equal to all of the electricity the entire world can generate in 200 days! And the thing is, many hurricanes don’t just last a day. They keep building as long as they keep getting energy from warm water. But if a hurricane moves over land or colder water (with temperatures below 26°C it loses its energy source. It starts to fizzle out.

The Rating System: How Do Hurricanes Rate?

Scientists use different systems to rate the intensity of hurricanes and other severe storms. The Beaufort scale classifies storms based on the speed of their winds. Category 1 weather is marked by no wind at all. Category 12 storms have wind speeds over 119 kph. That’s the lowest level of a hurricane.
The Saffir-Simpson scale was designed to measure hurricanes. It picks up where the Beaufort scale leaves off. Category 1 hurricanes on the Saffir-Simpson scale correspond to low-end Category 12 storms on the Beaufort scale. The Saffir-Simpson scale goes up to Category 5 - wind speeds more than 250 kph. Hurricane Katrina, the storm that devastated New Orleans in 2005, was a Category 5 hurricane.
Saffir-Simpson Scale

Movement and Direction

Hurricanes and cyclones
Hurricanes and cyclones may spin different directions but they're both powerful storms that have both positive and negative effects.
Hurricanes are constantly moving. Air currents in the atmosphere—as high as 15,250 meters - push them along. These air currents are called steering winds because they seem to steer hurricanes.
As the winds move, they spin. This is due to something called the Coriolis effect.  In the Northern Hemisphere, hurricanes spin counterclockwise. In the Southern Hemisphere, hurricanes spin clockwise.

Hurricane Damage at Sea and on Shore

Hurricane Wilma
Hurricane Wilma's strong winds and heavy rains forced people to wade through the flooded streets of Havana.
©Ernesto Garcia
Hurricanes that stay out at sea can cause such high waves, powerful winds, and heavy rain that even huge cargo ships can be blown off course or wrecked. But a hurricane that reaches land can be a real killer.
Because a hurricane can be hundreds of kilometers across, people in the area begin to feel the effects hours before it reaches land.  The winds arrive first, bringing lots of rain. Strong winds blow roofs off buildings and knock down trees and power lines. The storm surge—a rise in sea level caused by hurricanes—is responsible for most hurricane-related deaths. The storm surge can cause sudden flooding and can even harm habitats where fish breed.
Mangrove forests have been destroyed for shrimp farms, leading to less protection from hurricane impact.
Some natural barriers such asmangroves help to buffer the shore from the impact of high winds, large waves, and erosion.  Conservation of mangrove areas has become an important part of coastal ecology and minimizes the negative impact of hurricanes.

Inland Damage

Hurricane Katrina
Hurricane Katrina left the people of New Orleans in the USA homeless. Many people stayed in temporary shelters at stadiums and school gyms.
©Robert Terrell
Flooding and mudslides are also problems farther inland because hurricane rains spread over such a wide area. The rotating winds of a hurricane can spin off into tornadoes. Flooding and heavy rains can destroy water treatment facilities, which can lead to pollutionand disease. Flooding can leave behind standing water, which can cause a bump in the mosquito population. And crowded shelters—filled with people who have lost their homes—make it easier for diseases to spread.

Are Hurricanes Good for Anything?

Believe it or not, hurricanes do bring some benefits. The most obvious one is that they bring rain. Too much can be catastrophic, but some regions depend on hurricanes for their rainfall. Half of Japan’s rainfall is the result of typhoons. In 1969, Hurricane Camille helped end the threat of a drought in parts of Tennessee and Kentucky in the USA.
Hurricane Camille
Hurricane Camille's powerful winds uprooted an entire tree that fell on a home.
Also, a hurricane churns up the water so much that surface water temperatures are lowered. Sometimes they’re lowered enough to make conditions less favorable for other hurricanes in the same area. Last, if it weren’t for hurricanes, the tropics would be too hot. Hurricanes suck up the heat and shift it away from the equator.

Studying and Forecasting Hurricanes

Scientists use a wide range of tools to study hurricanes. Weathersatellites can track storms from space. Radar can follow storms as they move across a state. (Some TV weather reporters use radar to watch storms move through a city!) Organizations like the National Oceanic and Atmospheric Administration (NOAA) also use airplanes to study hurricanes and other weather. Planes fly into hurricanes and release tubes called dropsondes into the eyes of hurricanes. Parachutes are attached to the dropsondes. Right before they splash down, they transmit important scientific readings to the airplane. These readings can tell scientists whether the hurricane is getting weaker or stronger.
Hurrican Monitoring
An airplane flies into a hurricane to monitor its conditions using special equipment.

What Do Scientists Learn?

Weather scientists, calledmeteorologists, study hurricanes so we can all be better prepared when they happen. By knowing how hurricanes form, how they travel, and what happens when they reach populated areas, we can stay safer and minimize the damage they cause.
Technology helps us better
    forecast the behavior of storms
Technology helps us better forecast the behavior of storms. Japan on September 20, 1996: The blue in the image represents low wind speeds and red the highest wind speeds on the ocean surface.

Alvin, Bertha, Christobal . . .

Different parts of the world use different lists of names for hurricanes and major storms. Usually the same names are rotated every four or six years. The first storm of the season is given the first name on that year’s list. The second storm of the season gets the second name, and so on. For really destructive storms, the World Meteorological Organization sometimes takes names off the list. Once is enough.

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