Hurricanes: Powerful natural disasters

Résumé du document

Current events often deal about natural disasters. Worldwide, many natural catastrophes happen every year: tornadoes, thunderstorms, floods, hail, drought, fire, seism, volcano activity. Theirs effects often are dramatic. Lately, we heard about the tsunami in Asia, and also about the seism in Pakistan. These phenomena were murderous. A hurricane is one of the most spectacular and powerful of weather systems. As is shown in the histogram at the top, a windstorm is also one of the most frequent of natural disasters, with 121 occurrences in 2004. First, I will introduce the different terms for hurricanes and theirs categories. Then, I will explain when, and where, hurricanes form. Besides, I will explain the formation and the structure of a hurricane. At last, I will quote the effects. Hurricanes are classified by form and intensity. A tropical depression is constituted of clouds and thunderstorms with surface winds of less than 63 kilometers per hour.

Extraits

[...] A HURRICANE Formation The hurricane formation is not fully understand yet, but scientists know five factors required to make it possible. First, sea surface temperature to a depth of 50 meters must be above 26.5 degrees Celsius. The primary energy source of a hurricane is the heat of condensation from water vapor. Thus, the global warming is a cause of the increase of the hurricane occurrence. The map on the left shows hurricane activity between 1903 and 1925, and between 1971 and 1994. The map on the left shows hurricane activity during the two others periods. [...]

[...] Then, hurricanes often destroy electric facility, bridges and roads, prohibiting vital communication and handicapping rescue efforts. Beyond, as we saw in New Orleans, an increase of crime can be provoked by people affected by damage. CONCLUSION Hurricanes are hard to observe and to anticipate. If a cyclone forms between 3000 and 5000 km of a coastline, it will arrive five or six days after. However, if it forms between 500 and 600 km, it will arrive in less than one day. As many natural disasters, hurricanes are more and more frequent. [...]

[...] As is show in the histogram, natural disasters soar. We must wonder about consequences of this. SOURCES http://en.wikipedia.org/wiki/Tropical_cyclone http://www.bbc.co.uk/science/hottopics/naturaldisasters/hurricanes.shtml http://www.aoml.noaa.gov/hrd/tcfaq/tcfaqHED.html Pictures Hurricane approaching a coastlines : http://re4sale.net/files/108469/Hurricane%20Francis.jpg Boat under a hurricane : http://www.atmosphere.mpg.de/media/archive/3786.jpg Damaged car : http://externalweb.nmt.edu/reslife/hail/hail%202/Hail%20Storm%20damage% 204.jpg Forest fire : http://www.cpawscalgary.org/graphics/forest-fire.jpg Hurricane : http://www.allmetsat.com/img/garde_cyclone125.jpg Turned down boat : http://www.nola.com/hurricane/photos/ Ruined houses : http://www.fema.gov/kids/p_hur.htm Graphs Natural disasters by disaster type : http://www.em-dat.net/ Tropical cyclone windspeed scale : http://tsr.mssl.ucl.ac.uk/tracker/dynamic/main_.html Cyclones by month : http://www.irbs.com/bowditch/pdf/chapt36.pdf Number of occurrences of windstorm disasters by country : 1974 2003 : http://www.em-dat.net/ Temperatures oscillation and hurricane activity : http://www.euronet.nl/users/e_wesker/atlhur.html Structure d'un cyclone : http://www.srh.weather.gov/srh/jetstream/tropics/images/hurr_cross.jpg Total number of natural disasters reported. [...]

[...] It is this area which causes the heaviest damage. Next, there is a dense area of clouds and very intense thunderstorm activity. It is named Central Dense Overcast (CDO) and contains eye and eyewall. Hurricanes often have a symmetrical CDO. A hurricane have a diameter from 300 to 500 km and moves slowly at speeds of 32-40 kilometres per hour. EFFECTS Lower-category hurricanes can inflict greater damage than higher- category hurricanes. Indeed, being biggest, they move more slowly. Thus, they are more time to do damage. [...]

[...] Last, as we saw before, hurricane formation is possible at a distance of 10 degrees of more from the equator. Structure First, a hurricane rotate around an area of low atmospheric pressure near of Earth's surface. In a strong hurricane, the air rising creates an area named eye. There, the atmospheric pressure is inversely proportional of the wind speed. Hurricanes of category 5 have lowest atmospheric pressures in their centre. Moreover, the temperatures at the surface are the coldest and the temperatures at the upper levels are the warmest of the hurricane. [...]