Explain where and why Hurricanes form and describe their main characteristics.
Explain where and why Hurricanes form and describe their main characteristics.
Hurricanes, also known as Typhoons, Cyclones and Willy Willies, are extremely powerful low-pressure systems. They are natural Disasters that are responsible for a great number of deaths as they are virtually unstoppable. They are most recurrently generated over the Atlantic and Pacific Oceans and most common in autumn when ocean temperatures are at their highest.
For a Hurricane to materialize, several basic conditions are compulsory. The location of the hurricane and where it operates is also important. Hurricanes will only form within 5? and about 20? North and South of the equator. Any closer and the hurricane will not form. This is because the hurricane relies on the Corriolis force to create the spinning motion characteristics. This force is not sufficient closer than 5? to the equator.
Another Location in which a Hurricane will form is over warm oceans with surface temperatures in excess of 27?C and are as deep as 60m. This is because the hurricane requires warm waters as they offer large quantities of heat. This heat, from the solar short-wave radiation and convectional currents, will heat the air above it. The warm air will then rise, cooling adiabatically until the air condenses. But the rising air alone does not make a Hurricane as this process of Convection rainfall occurs around the globe frequently.
Existing Cyclonic winds, in the lower troposphere will need to be in the above locations. These can be caused in a number of ways i.e. Compact Depression. The speed of these winds will need to reach approximately 75mph (120kph) to be classified as a hurricane.
Other Location factors that help the hurricane form are areas with relative stable and uniform atmospheric temperatures, humidity (of over 60% to provide sufficient energy) and pressure. There must also be little change of horizontal wind with height.
There are many different characteristics to a hurricane. Some of these distinctive features ...
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Existing Cyclonic winds, in the lower troposphere will need to be in the above locations. These can be caused in a number of ways i.e. Compact Depression. The speed of these winds will need to reach approximately 75mph (120kph) to be classified as a hurricane.
Other Location factors that help the hurricane form are areas with relative stable and uniform atmospheric temperatures, humidity (of over 60% to provide sufficient energy) and pressure. There must also be little change of horizontal wind with height.
There are many different characteristics to a hurricane. Some of these distinctive features are shown in the diagrams below.
Hurricanes can reach up beyond 16km. One characteristic of a hurricane is the eye. The eye, within the spiral structure of the storm, is unique to hurricanes. It can be between 20km and 60 km in width. In the eye, winds are light and skies are clear or partly cloudy, due to descending air in the centre of the storm, warming adiabatically and therefore become stable. However, this is a deceptive calm as maximum-force winds and torrential rains border it. Many people have been injured or killed when they ventured out from a safe shelter during the calm of the hurricane's eye, only to be caught in the maximum-force winds at the far side of the eye which blow in the opposite direction from the winds in the leading half of the storm. These winds are responsible for flying debris, one of the greatest dangers during a hurricane.
Air moves in a large, tightening spiral around the eye. This air is of extremely low pressure. In the Northern Hemisphere the wind circulation is counter clockwise, due to the corriolis force acting on the earth, and reaches maximum velocity in a circular band extending outward 20 to 30 miles from the rim of the eye. Near the eye winds may gust to more than 200 miles per hour (174 knots). Winds of 39 miles per hour (34 knots) and greater can extend 200 miles or more in all directions from the centre of the hurricane. The entire storm dominates the ocean surface and lower atmosphere over thousands of square miles.
As well as strong winds in the hurricane, another common feature is heavy rainfall. This intense rainfall is due to the rapid cooling and rising of the air. The slower the hurricane travels the more rainfall there will be. Amounts of rainfall can exceed 500mm per day, which in contrast is a year's amount of precipitation in some areas of England. There is low pressure near the surface of a hurricane. A steep pressure gradient is formed inside the hurricane, as fast winds are transferred form areas of low pressure to areas of high pressure. The average pressure for a hurricane is approximately 950mb.
For a named example, describe how hurricanes can affect human activity.
Example - Hurricane Mitch
Beginning in the Caribbean, Hurricane Mitch affected and destroyed many regions in Honduras, Nicaragua and Costa Rica. When it hit, the constant rain was unexpected. Hurricane Mitch delivered more water over Central America than most of the regions received in a year. This rain caused the cone of a volcano to burst open the mountainside. A mudslide resulted that destroyed 4 villages with a layer of mud 6 metres high.
At its most destructive, winds were recorded at 300kph. Most damage however, had been caused by a weeks worth of heavy precipitation. Huge floods and mudslides were caused which resulted in thousands of deaths and hundreds of thousands of homes destroyed. Bridges, roads, power lines and cattle farms were swept aside, to name only a few other affected areas.
In Honduras, 17,000 were killed as whole villages were destroyed as well as neighbouring cities. Some towns were completely smashed. About one third of all people in Honduras were affected, many of who were under the age of 25 years. The infrastructure, including schools, was affected with major consequences.
In Nicaragua, up to 2,100 people were killed at the Casita volcano and elsewhere. Water supplies and other utilities were disrupted due to the amount of dead bodies. There were also fears off epidemics, including Malaria and Cholera. A vast lake was formed in the city centre of Tegucigalpa as the Rio Choluteca became swollen. Shantytowns also lied in ruin. The homeless count was 800,000, of the countries 5 million inhabitants. Crime rate increased (over 200people arrested in 1 day) and businesses were looted. Major route ways were also destroyed as 50 bridges on highways fell victim to the hurricane. Hundreds off small villages were entirely cut-off. The cost off food rocketed because of shortages.
Hurricane Mitch had destroyed countries that relied on crops and agriculture for income. Up to 70% of Honduras's income had been lost. It was also estimated that productions costs in the area totalled $1.5bn (£903million). Over half these losses are in the agricultural sector. Many foods that are exported from Central America e.g. Bananas and coffee were also destroyed. Due to the extended and unpredictable path of hurricane Mitch, a much wider piece of the regions agriculture base in Central America was destroyed. This was unanticipated as hurricanes are usually associated with coastal areas.
In all, hurricane Mitch had destroyed all leads of life in many of the Central American countries, notably Honduras and Nicaragua.
HURRICANE ESSAY
JAMES WARNES Page 1 4/30/2007
