Natural Disasters: Cyclones

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CYCLONES

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Cyclonic-force winds may be encountered all over the
globe, but it is only above the warm seas of the tropics that
a ripple of instability in the air can become a genuine
cyclone, the deepest of all low-pressure weather systems.

What is a Cyclone? How do Cyclones occur? When and where do Cyclones occur? Why do Cyclones occur? Cyclone Danger Major Cyclones, Hurricanes and Typhoons Cyclone Tracy Case Study

What is a Cyclone?

Cyclones are huge revolving storms caused by winds blowing around a central area of low atmospheric pressure. In the northern hemisphere, cyclones are called hurricanes or typhoons and their winds blow in an anti-clockwise circle. In the southern hemisphere, these tropical storms are known as cyclones, whose winds blow in a clockwise circle.

How do Cyclones occur?

Cyclones develop over warm seas near the Equator. Air heated by the sun rises very swiftly, which creates areas of very low pressure. As the warm air rises, it becomes loaded with moisture which condenses into massive thunderclouds. Cool air rushes in to fill the void that is left, but because of the constant turning of the Earth on its axis, the air is bent inwards and then spirals upwards with great force. The swirling winds rotate faster and faster, forming a huge circle which can be up to 2,000 km across. At the centre of the storm is a calm, cloudless area called the eye, where there is no rain, and the winds are fairly light.

As the cyclone builds up it begins to move. It is sustained by a steady flow of warm, moist air. The strongest winds and heaviest rains are found in the towering clouds which merge into a wall about 20-30 km from the storm’s centre. Winds around the eye can reach speeds of up to 200 km/h, and a fully developed cyclone pumps out about two million tonnes of air per second. This results in more rain being released in a day than falls in a year in a city like London.

When and where do Cyclones occur?

Cyclones begin in tropical regions, such as northern Australia, South-East Asia and many Pacific islands. They sometimes drift into the temperate coastal areas, threatening more heavily populated regions to the South. Northern Australia has about four or five tropical cyclones every year during the summertime wet season. For a cyclone to develop, the sea surface must have a temperature of at least 26ºC.

Why do Cyclones occur?

When warm air rises from the seas and condenses into clouds, massive amounts of heat are released. The result of this mixture of heat and moisture is often a collection of thunderstorms, from which a tropical storm can develop.

The trigger for most Atlantic hurricanes is an easterly wave, a band of low pressure moving westwards, which may have begun as an African thunderstorm. Vigorous thunderstorms and high winds combine to create a cluster of thunderstorms which can become the seedling for a tropical storm.

Typhoons in the Far East and Cyclones in the Indian Ocean often develop from a thunderstorm in the equatorial trough. During the hurricane season, the Coriolis effect of the Earth’s rotation starts the winds in the thunderstorm spinning in a circular motion.

Cyclone Danger

Cyclones create several dangers for people living around tropical areas. The most destructive force of a cyclone comes from the fierce winds. These winds are strong enough to easily topple fences, sheds, trees, power poles and caravans, while hurling helpless people through the air. Many people are killed when the cyclone’s winds cause buildings to collapse and houses to completely blow away.

A cyclone typically churns up the sea, causing giant waves and surges of water known as storm surges. The water of a storm surge rushes inland with deadly power, flooding low-lying coastal areas. The rains from cyclones are also heavy enough to cause serious flooding, especially along river areas.

Long after a cyclone has passed, road and rail transport can still be blocked by floodwaters. Safe lighting of homes and proper refrigeration of food may be impossible because of failing power supplies. Water often becomes contaminated from dead animals or rotting food, and people are threatened with diseases like gastroenteritis.

Major Cyclones, Hurricanes and Typhoons

Year	Area of Cyclone	Death toll (est.)
1900	Galveston, Texas, USA	10 000 - 12 000
1906	Society and Cook Islands	10 000
1963	Bangladesh	15 000
1964 (May)	Bangladesh	35 000
1965 (Jun)	Bangladesh	15 000
1970	Caribbean coast	1 000 000
1977	Honduras	100 000
1985	South-eastern India	15 000 - 100 000
1991	Bangladesh	139 000

Cyclones and Anticyclones

Cyclones are areas of low pressure. Cyclones usually exhibit nearly circular isobars. If isobars are oblong or elongate with the lowest pressure near the center we call them troughs. As air enters an area of low pressure from all directions, the Coriolis effect bends the direction of the wind to the right of its path. This creates a counterclockwise rotation around the low and  convergence near the center of the system. As the air collides near the center it is forced aloft where divergence takes air away from the center of the system. The upper-level divergence is necessary for the system to be maintained as an area of low pressure. Without the divergence, the system would fill with air and the horizontal pressure differences would be equalized causing the system to dissipate. Anticyclones are areas of high pressure that exhibit nearly circular isobars. If isobars are oblong or elongate with the highest pressure near the center we call them ridges. For high pressure areas, air descends toward the surface due to convergence aloft. As the air nears  the surface it is forced outward (divergence) from the center. The Coriolis effect bends the air to the right of its path creating a clockwise rotation around the high.

Figure PC.6 Circulation within a low pressure system in the Northern Hemisphere

Figure PC.7 Circulation within a high pressure system in the Northern Hemisphere

Figure PC.8 Cyclone in the Southern Hemisphere 
(Click image to enlarge)

Because the Coriolis effect works in the opposite direction in the Southern Hemisphere, circulation around lows are clockwise and inward toward the center at the surface and highs exhibit a diverging, counterclockwise rotation. You can see this effect in the cloud pattern created by a cyclone in the Southern Hemisphere.

Anticyclones

The United Kingdom Environmental Change Network

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Anticyclones (High Pressure)

 

Areas of sinking air which result in high pressure are called anticyclones.   The opposite to an anticyclone is the cyclone or depression. 

High pressure systems have low pressure gradients (ie the air pressure doesn’t change rapidly).  This means that the winds are gentle.   As the air sinks, it warms up, leading to warm and dry weather. 

Anticyclones are much larger than depressions and can lead to many days or weeks of settled and calm weather.  Anticyclones often block the path of depressions, either slowing down the bad weather, or forcing it round the outside of the high pressure system.  They are then called ‘Blocking Highs‘.

As air descends, air pressure increases.  When air hits the ground, it has to go somewhere.  The earth’s rotation makes the air change direction.   In the Northern Hemisphere the air is pushed clockwise.  In the Southern Hemisphere the air is pushed anticlockwise.  This can be seen in the diagram below.

Air Direction in High and Low Pressure Systems

http://www.itl.net/education/online/weather/high.html

 

Weather conditions can vary between summer and winter anticyclones.  Do you want to look at summer or winter anticyclones?

                                                                                       

Characteristics of Summer Anticyclones Hot days with few or no clouds. Light winds. Cooling of ground leading to morning mist. Warm moist air rising from the ground forming thunderstorms. Cloud cover over Eastern England caused by light winds blowing over the cooler North Sea.

Characteristics of Winter Anticyclones Cloudless skies but less radiation due to the low angle of the sun. Temperature drop, making the days cold and the nights even colder due to lack of cloud cover. Fog and frost forming at night. Cold air from Asia bringing snow to the East.

BrahMos cruise missile test fired for 15th time

Thursday, 06 March , 2008, 08:04

New Delhi: The BrahMos supersonic cruise missile that India and Russia have jointly developed was successfully launched for the 15th time on Wednesday - and for the first time from a naval ship toward a land based target, a defence ministry official said. Fired from the frontline Indian Navy warship INS Rajput, the missile successfully impacted on its target in the Andaman & Nicobar Island chain, the official added. “The missile met all the parameters during its launch, flight and selection of the designated target from among a group of targets and hit precisely, destroying the target,” the official said. For more news, analysis click here>> “This mission was very important as it has established the sea-to-land attack capability of the missile,” he added. Scientists of the Defence Research and Development Organisation (DRDO), who have been involved in the joint development of the missile with their Russian counterparts, conducted the launch with the support of the Andaman and Nicobar Command (ANC) that deployed 10 ships, three aircraft and three helicopters for logistics support. A Sivathanu Pilla, CEO and managing director of missile builder BrahMos Aerospace, Rear Admiral P K Nair, the officiating head of the ANC, were among those who witnessed the launch. Defence Minister A K Antony congratulated the DRDO scientists and the Indian Navy for the successful missile launch. The DRDO and Russia’s NPO Mashinostroyenia have jointly developed the BrahMos, which is named after the Bramaputra and the Moskova, the two major rivers of India and Russia respectively. Work on the project began in 1998 and the missile was first test fired on December 22, 2004. BrahMos is a two-stage missile with a solid propellant booster and a liquid propellant ram jet system that gives it a 300-km range. The Indian Army is currently preparing to operationalise at least one regiment of the BrahMos missile mounted on a mobile launcher. The triple-barrelled launcher is capable of firing the missile singly or in salvos of two or three. Work is also progressing on an Indian Air Force version that will be delivered from the Sukhoi SU-30MKI platform.

The Basics of Global Warming

The greenhouse effect

The atmosphere has a natural supply of “greenhouse gases.” They capture heat and keep the surface of the Earth warm enough for us to live on. Without the greenhouse effect, the planet would be an uninhabitable, frozen wasteland.

Before the Industrial Revolution, the amount of carbon dioxide (CO₂) and other greenhouse gases released into the atmosphere was in a rough balance with what could be stored on Earth. Natural emissions of heat-trapping gases matched what could be absorbed in natural sinks. For example, plants take in CO₂ when they grow in spring and summer, and release it back to the atmosphere when they decay and die in fall and winter.

Too much greenhouse effect

Industry took off in the mid-1700s, and people started emitting large amounts of greenhouse gases. Fossil fuels were burned more and more to run our cars, trucks, factories, planes and power plants, adding to the natural supply of greenhouse gases. The gases—which can stay in the atmosphere for at least fifty years and up to centuries—are building up beyond the Earth’s capacity to remove them and, in effect, creating an extra-thick heat blanket around the Earth.

The result is that the globe has heated up by about one degree Fahrenheit over the past century—and it has heated up more intensely over the past two decades.

If one degree doesn’t sound like a lot, consider this: the difference in global average temperatures between modern times and the last ice age—when much of Canada and the northern U.S. were covered with thick ice sheets—was only about 9 degrees Fahrenheit. So in fact one degree is very significant—especially since the unnatural warming will continue as long as we keep putting extra greenhouse gases in the atmosphere.

How much is too much?

Already, people have increased the amount of CO₂, the chief global warming pollutant, in the atmosphere to 31 percent above pre-industrial levels. There is more CO₂ in the atmosphere now than at any time in the last 650,000 years. Studies of the Earth’s climate history show that even small changes in CO₂ levels generally have come with significant shifts in the global average temperature.

Scientists expect that, in the absence of effective policies to reduce greenhouse gas pollution, the global average temperature will increase another 2.0 degrees Fahrenheit to 11.5 degrees Fahrenheit by 2100.

Even if the temperature change is at the small end of the predictions, the alterations to the climate are expected to be serious: more intense storms, more pronounced droughts, coastal areas more severely eroded by rising seas. At the high end of the predictions, the world could face abrupt, catastrophic and irreversible consequences. Find out more about what a warmer world could look like.

The science is clear

Scientists are no longer debating the basic facts of climate change. In February 2007, the thousands of scientific experts collectively known as the Intergovernmental Panel on Climate Change (IPCC) concluded that there is greater than 90 percent likelihood that people are causing global warming. (IPCC, 2007)

These latest findings amplify what other highly respected science organizations say:

• In a joint statement with 10 other National Academies of Science, the U.S. National Academy of Sciences said:

“The scientific understanding of climate change is now sufficiently clear to justify nations taking prompt action. It is vital that all nations identify cost-effective steps that they can take now, to contribute to substantial and long-term reduction in net global greenhouse gas emissions.”—Joint Statement of Science Academies: Global Response to Climate Change, 2005

• The American Geophysical Union, a respected organization comprising over 41,000 Earth and space scientists, wrote in its position on climate change that “natural influences cannot explain the rapid increase in global near-surface temperatures observed during the second half of the 20th century.”

What You Can Do

Small changes to your daily routine can add up to big differences in helping to stop global warming.

• Three easy ways to fight global warming »
• Spread the word — Email this page to a friend »

Sources

“Human Impacts on Climate,” American Geophysical Union, www.agu.org/sci_soc/policy/climate_change_position.html, December 2003.

Intergovernmental Panel on Climate Change (IPCC). “Climate Change 2001: Working Group I: The Scientific Basis.” www.grida.no/climate/ipcc_tar/wg1/044.htm.

Intergovernmental Panel on Climate Change (IPCC). “Climate Change 2007: The Physical Scientific Basis”: Summary for Policymakers. www.ipcc.ch/SPM2feb07.pdf.

Naomi Oreskes. Beyond the Ivory Tower: The Scientific Consensus on Climate Change. Science. 3 December 2004. Vol. 306. no. 5702, p. 1686 DOt 10.1126/science.1103618. www.sciencemag.org/cgi/content/full/306/5702/1686

“Joint Science Academies’ Statement: Global Response to Climate Change,” www.royalsoc.ac.uk/document.asp?latest=1&id=3222, 7 Jun 2005, (The National Academies that signed the statement are the United States, England, Germany, Japan, Russia, France, Italy, Canada, Brazil, China and India).

The Dangers   .   The Science   .   Calculate Your Impact   .   What You Can D

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