http://www.articletrader.com/ Articles at ArticleTrader en-us http://www.articletrader.com/science/environment/theoretical-concept-of-hail.html http://www.articletrader.com/science/environment/theoretical-concept-of-hail.html Fri, 17 Nov 2006 00:00:00 -0600
Precipitation is one form of hail. Hail in other sense means falling of balls or irregular lumps of ice (hailstones), 5 mm–50 mm in diameter on average, with much larger reported from severe thunderstorms. Thunderstorms always produced by cumulonimbus. small hailstones are >5 mm in diameter. They are layered and can be irregular and clumped together.

Hail formation:

Hail forms when there is condensation nuclei such as dust, bugs, or ice crystals, when supercooled water freezes on contact. When clouds contain large numbers of supercooled water droplets, these ice nuclei grow quickly at the expense of the liquid droplets because the saturation vapor pressure over ice is slightly less than the saturation vapor pressure over water. When the hailstones grow large enough, latent heat released by further freezing may melt the outer shell of the hailstone. The growth that follows is called wet growth, which is usually more efficient because the liquid outer shell allows the stone to accrete other smaller hailstones in addition to supercooled droplets. These winds hold the rain and freeze it. As the process repeats, the hail grows increasingly larger
Ideal conditions for hail formation:
1. When there are strong thunderstorm clouds, particularly those with intense updrafts, high liquid water content, great vertical extent, large water droplets, and where a good portion of the cloud layer is below freezing (< 32 °F (0 °C)). The growth rate is maximized at about -13 °C (9 °F) then hail forms.
2. during early summer where surface temperatures are warm enough to promote the instability associated with strong thunderstorms, but the upper atmosphere is still cool enough to support ice. Accordingly, hail is actually less common in the tropics despite a much higher frequency of thunderstorms than in the midlatitudes because the atmosphere over the tropics tends to be warmer over a much greater depth. Then hail forms.
3. also when dry air into strong thunderstorms over continents can increase the frequency of hail by promoting evaporational cooling which lowers the freezing level of thunderstorm clouds giving hail a larger volume to grow in.

Deadly hailstorms:

1. several hundred pilgrims were killed by a massive hailstorm in Roopkund, Uttaranchal, India.[4].
2. $150 million in damage when softball-sized hail hit Calgary, Canada on July 28, 1981.
3. Softball-sized hail destroyed roofs and cars, causing $625 million in total damage in Denver, Colorado, USA.
4. a Labour Day thunderstorm caused $400 million worth of insurable damage in Calgary, Canada. Thirteen additional hailstorms between 1981 and 1998 caused an estimated $600 million in damage in the Calgary area alone.
5. Dallas and Fort Worth, Texas, USA, $1.1 billion insured losses on May 5, 1995.
6. $1.6 billion. 20,000 properties and 40,000 vehicles were damaged during the storm with more than 25 aircraft damaged at Sydney Airport, one person was killed while fishing after getting struck by lightning and several other people were injured. It was the costliest hailstorm to hit an Australian populated city on April 14, 1999 in New South Wales, Australia.



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Author: Pacific Disaster Center


The Pacific Disaster Center's mission is to provide applied information research and support for the development of more effective policies and, programs, for the disaster management. PDC give information and help during times of natural disaster. PDC Helps people during Natural calamities


Source: http://www.articletrader.com ]]> http://www.articletrader.com/science/environment/introduction-to-tsunami-and-its-preventions.html http://www.articletrader.com/science/environment/introduction-to-tsunami-and-its-preventions.html Tue, 14 Nov 2006 00:00:00 -0600
when a body of water, such as an ocean is rapidly displaced on a massive scale then we call it tsunami. It Is a series of waves. The effects of a tsunami can range from unnoticeable to devastating. There are various reasons behind the tsunami.
1.earthquakes.
2.mass movements.
3.Volcanic erosions.
4.Under water explosions.
5.Meteorite impacts.
The term tsunami comes from the Japanese language meaning harbour. tsunami is used for both the singular and plural. The term was created by fishermen.

Causes:

1.it happens when the sea floor abruptly deforms and vertically displaces the overlying water.
2.it also happens because of the large vertical movements of the Earth’s crust can occur at plate boundaries.
3.Subduction earthquakes are particularly effective in generating tsunamis.
4.too much stress is put on the lip and it snaps back, sending shockwaves through the Earth’s crust, causing a tremor under the sea, known as an Undersea Earthquake.
5.Sub-marine landslides and collapses of volcanic edifices may also disturb the overlying water column.
6.violent submarine volcanic eruption can uplift the water column and form a tsunami.

Tsunami wave:

The ocean waves are divided into three groups. They are characterized by depth.
1.Deep water.
2.Intermediate water.
3.Shallow water.

tsunami waves are considered shallow-water waves. As the wave approaches the shallow waters of shore, its time period remains the same, but its wavelength decreases rapidly, thus causing the water to pile up to form tremendous crests, in an effect known as "shoaling".

Signs of an approaching tsunami:

1.An earthquake may be felt.
2.Large quantities of gas may bubble to the water surface and make the sea look as if it is boiling.
3.The water in the waves may be unusually hot.
4.The water may smell of rotten eggs or of petrol or oil.
5.A thunderous boom may be heard then a a roaring noise as of a jet plane or a whistling sound.
6.The water may sting the skin.
7.A flash of red light might be seen near the horizon.
8.The sea may recede to a considerable distance.

Warnings and prevention:

Tsunamis cannot be prevented or precisely predicted
1.Regions with a high risk of tsunamis may use tsunami warning systems to detect tsunamis and warn the general population before the wave reaches land.
2.Computer models can roughly predict tsunami arrival and impact based on information about the event that triggered it and the shape of the seafloor and coastal land.
3.the early warnings comes from nearby animals.
4.building tsunami walls of up to 4.5 m (13.5 ft) high in front of populated coastal areas.
5.floodgates and channels to redirect the water from incoming tsunamis.
6.Environmentalists have suggested tree planting along stretches of sea coast which are prone to tsunami risks, it would take some years for the trees to grow to a useful size. And such plantations could offer a much cheaper and longer-lasting means of tsunami mitigation.




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Author: Pacific Disaster Center


The Pacific Disaster Center's mission is to provide applied information research and support for the development of more effective policies and, programs, for the disaster management. PDC give information and help during times of natural disaster. PDC Helps people during Natural calamities


Source: http://www.articletrader.com ]]> http://www.articletrader.com/science/environment/information-about-the-floods.html http://www.articletrader.com/science/environment/information-about-the-floods.html Fri, 10 Nov 2006 00:00:00 -0600 Types of Floods:
1. River flood: this is a naturally occurring flood. Some are seasonal, occurring only during a particular season; say winter or spring, when melting snow combines with spring rains, filling the river valley with too much water, thus flooding the miles of land present around it.
2. Coastal flood: These kinds of floods are caused due to the winds generated by intense low pressure systems which drive ocean water inland causing intense flooding. Coastal floods are also caused by tsunamis, or tidal waves, which are produced by earth quakes. Beaches and coastal houses are swept away by the water causing intense destruction.

3. Urban food: Urbanisation causes what is called deforestation which includes conversion of fields and woodlands into commercial purposes, thus decreasing the water absorbing capacity of the land. This factor amplifies the magnitude of the floods and streets become swift mirrors. The damage cost is high in these types of floods as they occur in commercial areas.

4. Flash flood: It is the most dangerous type of floods as it is the fastest moving types and comes without warning. It is a specific type of flood that appears and moves quickly across the land, catching people off guard and unprepared .the causes of these types of floods include highly concentrated rainfall, repeated thunderstorms or tropical storms. Dam failures create the worst type of flash flooding as a large quantity of water is suddenly let loose downstream, destroying any thing that obstructs its path. Water can rise up to the height of 20 feet, carrying a huge amount of debris along with it.
5. Ice jam: Floating ice can accumulate at a natural or man-made obstruction and stop the flow of water.

Effects of floods: Soil erosion is one of the most prominent effects of floods. The people affected by floods are cut off by the rest of the country and most means of contact are disabled. The amount of food if insufficient can be another cause of death after a flood occurs. Flood water destroys several granaries, fisheries and standing crops. Several roads are submerged in water. Floods can cause land slides and debris slides which are quite catastrophic in nature.

Prevention of floods: Changing land use from farmland should be stopped. Construction of dams and levees reduce the risk of floods to a large extent.. Zoning restrictions limit flood damage. Governments should pass laws preventing uncontrolled building on flood plains to limit flood risks and to protect nearby property.


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Author: Pacific Disaster Center


The Pacific Disaster Center's mission is to provide applied information research and support for the development of more effective policies and, programs, for the disaster management. PDC give information and help during times of natural disaster. PDC Helps people during Natural calamities


Source: http://www.articletrader.com ]]>