The back of our truck was home on San Salvador in the Bahamas
|
|
Of all of the natural disasters that occur around the world, few are as completely devastating as hurricanes, also called tropical cyclones. These storms are so powerful that they release more energy per day than the worldÕs consumption rate of energy. In fact, they release 70-times as much energy, the same as a 10-megaton nuclear weapon being detonated every 20 minutes. Obviously these storms are something to be respected due to their sheer power, and they are an interesting topic of research for many scientists. In this paper I will go over a general background of hurricanes, the effects that they have on ecosystems, the effects on human populations, how ENSO influences them, and what we can look to see in the future.
To start, there are several intensity classifications that need to be discussed. The lowest classification is a tropical depression, which has winds that are less than 39 mph. These storms already are established as low-pressure systems, but they have no eye, which is discussed in more detail later in this paper. The next classification is a tropical storm. These storms have wind speeds between 39-73 mph. They still donÕt have an eye, but they do have a cyclonic shape. Once wind speeds reach over 74 mph the storm becomes a tropical cyclone. It then has a cyclonic shape, an eye, an eye wall, and can reach estimated maximum speeds of 195 mph. In different parts of the world, tropical cyclones are referred to by different names. In the Pacific they are generally called typhoons, while in the Atlantic they are known as hurricanes. In areas south of the equator they have other names, but typically they are called simply cyclones.
Tropical cyclones are low-pressure systems that spin in a circle as they travel. Due to the Coriolis effect, in the northern hemisphere storms spin counter-clockwise, while in the southern hemisphere they spin clockwise. This is because surface winds deflect as they near the eye of the hurricane; to the right in the northern hemisphere, and to the left in the southern. This motion causes the system to spin, and also pushes it westward and poleward throughout its life. This poleward motion is also attributed to the Coriolis effect. The closer to the equator, the weaker the influence of the Coriolis effect. Therefore, the portion of the system farthest form the equator will have a stronger deflection in the wind, subsequently driving the cyclone towards the poles.
There are several conditions that are usually present in order for a hurricane to form, but every criteria doesnÕt always have to be met. The water temperature must be at least 79.7¡F, and it must maintain that temperature down to 160ft. deep. Also, there must be a rapid cooling of air as elevation increases, along with high levels of humidity and low wind shear. Typically cyclones must form more than 5¡ of latitude from the equator. This is because the coriolis effects are too weak, as mentioned earlier, to cause the spiral motion of the system. However, there have been several occurrences in history of hurricanes forming within these latitudinal boundaries. In 2001, Tropical Storm Vamei formed at 1.4¡N in the South China Sea. Again in 2004, Cyclone Agni Reached as far south as 0.7¡N, and at first was thought to have crossed the equator, becoming an anticyclonic circulation in the southern hemisphere, but later findings indicated that it had stayed in the northern hemisphere.
Tropical cyclones occur in seasons, with each hurricane basin having a different season where they experience the majority of hurricanes. The peak time of the year for the entire world is during the summer months, when the difference between atmospheric temperature and sea surface temperature is the greatest. In general, September is the most active month for hurricanes, and November is the only month where all of the hurricane basins are active.
A hurricane forms when warm air at the sea surface is driven upwards. As the air rises, it is cooled and the water vapor is condensed at the top. This cooler, denser air is driven outwards creating a stadium effect at the top of the eye. The eye is the center of the hurricane, and is known for having very calm conditions within it as compared to the rest of the system. It is caused by a stream of sinking air at the center, and can reach sizes of 2-230 miles in diameter. Sometimes the eye can be viewed from space as a clear dot in the middle of the cyclone; however there occasionally are thunderstorms that will cover the eye from above. Surrounding the eye is the eye wall, which is somewhat like a cylinder of thunderstorms where the most intense wind speeds can be found. As the cold, dense air moves upward and outwards, it creates a series of rain bands. The size of a hurricane can be determined by finding the distance between the eye and the outermost rain band, and seeing how many degrees of latitude the system covers. The classifications of these sizes are less than 2¡ is a midget, 2-3¡ is small, 3-6¡ is medium or average, 6-8¡ is a large system, and more than 8¡ is very large. Tropical cyclones are also measured by the intensity of their wind speed. The Saffir-Simpson rating scales has 5 categories that a cyclone can fall into. Level 1 is a storm having sustained wind speeds over 74 mph, while a category 5 storm will have sustained wind speeds of over 156 mph. However, wind isnÕt the only weapon that hurricanes have. Within the eye of a hurricane, some of the lowest pressures found on Earth can be found. Because of this, a mound develops on the ocean surface beneath the eye, called the storm surge, and is the real killer in a hurricane. 90% of all cyclone deaths are attributed to the storm surge because it causes massive flooding when it hits land.
Hurricanes have dramatic effects on ecosystems they come in contact with, which includes both marine and terrestrial ecosystems. In 1996, Hurricane Fran hit North Carolina, causing water quality problems for weeks. The storm caused a sewage treatment plant to lose power, releasing untreated human waste into the rivers. Also, several swine waste lagoons overflowed due to flooding which added concentrated organic waste to the water. This, on top of the natural spillage of swamp water into the rivers, caused a massive fish kill in the area because the oxygen content in the water had dropped to 0% in some places. Another example is of Hurricane Hugo, which hit both Puerto Rico and South Carolina in 1989. The storm surge destroyed coastal pine forests by inundating them with salt water. The category 5 winds tore off branches and uprooted trees, adding a large amount of nutrients to the soil and affecting the soil system. Landslides are a secondary effect from the added water to the soil. Due to loss of habitat and food sources, animals are also greatly affected by hurricanes on land. In the ocean, many organisms have adapted to the destruction that is associated with hurricanes. Elk Horn coral is one species that depends on disturbances like hurricanes to reproduce. It has long, extending branches that resemble the horns of elk, and when they are broken off in a storm, they begin forming a new organism where the broken piece comes to rest. However, there are many other species on the reef that do not fair so well in these conditions, and hurricanes can destroy entire sections of a coral reef.
The effects of hurricanes on humans come in several different forms. The most obvious are the destruction of property due to high winds and flooding, and the loss of life. Hurricanes damage vehicles, buildings, bridges, and blow loose debris everywhere. Sometimes the winds will form tornadoes when they reach land in areas where they are normally not present. They also disrupt international shipping lanes, causing delays and sometimes shipwrecks. Cyclones can also have a much larger effect on the economy. When Hurricane Wilma hit Cancun, Mexico in 2005, much of the city was destroyed, causing tourism to fall dramatically. Tourism in Cancun is one of MexicoÕs largest sources of revenue, so this hurricane affected the entire countryÕs economy.
Scientists have gone to great efforts to try to predict, and warn against tropical cyclones. There are six Regional Specialized Meteorological Centers (RSMCs) that are in charge of issuing bulletins, warnings, and advisories in the event of a hurricane. There are also six Tropical Cyclone Warning Centers (TCWCs) that are responsible for providing information to smaller regions. Scientists have found it extremely difficult to predict the intensity of a storm, but are able to predict the track that a storm will take. They use prediction software that is based on the strength and position of high and low-pressure systems that are in the hurricaneÕs path. They also use satellites to view the progress from above, and Doppler radar once the storm nears land. The Doppler system is also able to determine a stormÕs intensity and position every several minutes. Scientists have explored the possibility of being able to cause hurricanes to weaken before they reach land. In the 1960Õs and 70Õs the US government tried to weaken tropical cyclones by seeding. This is a process of putting silver iodide into select thunderstorms. The idea was to cool the outer rain belts enough to cause them to freeze, and hopefully collapse the eye wall. In the end, this approach proved unsuccessful, and the project was abandoned. Other solutions have been put forth, including towing icebergs into the eye of the hurricane, blasting it with nuclear weapons, and even throwing dry ice into the eye. However, all of these solutions suffer, whether they are plausible or not, from the fact that cyclones are simply too large for any of the weakening techniques to be practical.
Over the last few decades there has been a lot of public exposure to a phenomenon called the El Ni–o-Southern Oscillation (ENSO). Air pressure in the Indian Ocean and the Pacific shifts like a seesaw, with one being high-pressure while the other has low-pressure, and vis versa. The effects of this are extreme changes in weather pattern for certain areas. For instance, the El Ni–o of 1997-98 caused severe fluxuations, including droughts and fires in one part of a country, while other parts are hit with hurricanes and floods. On the other extreme, La Ni–a events are basically the opposite of El Ni–o events. These extremes can affect the frequency and intensity of weather systems like hurricanes. For example, the Caribbean experiences mild hurricane seasons during El Ni–o but have devastating storms in La Ni–a. This is not an unusual happening; the ENSO is a naturally occurring weather cycle. However, it is thought that due to climate change effects, these extremes will become more drastic.
There is much debate over whether or not climate change has an effect on the frequency and intensity of hurricanes. One argument against this theory is that since tropical cyclones are formed in such variability, any human impact on conditions would be tiny in comparison. Therefore, it cannot be proven that increases the frequency of hurricanes is directly attributed to human inputs. However, it has been shown that the strongest hurricanes are getting stronger. In 1981, the average wind speed of hurricanes worldwide was 140 mph. In 2006, this number had jumped to 156 mph. Over this same time period, the ocean temperature globally has increased from 82.8¡F to 83.3¡F. This seems to be an extremely small increase, but the effects of a temperature change even this small is magnified by nature. Scientists believe that, even though warming temperature of surface water may not aide in increasing the ability for a hurricane to form, it does provide more fuel to power the hurricane once it has formed. This may explain the previous statement of the strongest hurricanes becoming stronger, without the increase in frequency.
It is apparent that we will have to live with hurricanes for some time to come, but that doesnÕt mean that it is a bad thing. Tropical cyclones move warm air and water to more temperate climates, which in turn maintain the EarthÕs relatively stable and warm temperature worldwide. These storms play an important role in ocean and atmospheric circulation. Despite the frequency of hurricanes staying at 87±10 annually worldwide, the intensity has increased. Average energy that is released has increased 70% in the last 30 years, along with the maximum wind speed and storm lifetime increasing 15% and 60% respectively over the same time frame. As our coastlines develop in the future and become more densely populated, hurricanes will also become more destructive financially. At this point, we can only try to protect our cities with sound land use, wind and flood resistant buildings, reliable forecasts, and public education of evacuation and refugee details. Hurricanes are a natural occurrence, and we have to be able to live with them as best we can.
Sources:
Black, R.A.; Bluestein, H.B.; Black, M.L. (1993). Unusually Strong Vertical Motions in a Caribbean Hurricane. Monthly Weather Review. 122, p. 2722-2739.
Cione, J.J.; Uhlhorn, E.W. (2003). Sea Surface Temperature Variability in Hurricanes: Implications with Respect to Intensity Change. American Meteorological Society. 131, p. 1783-1796.
Donnelly, J.P.; Woodruff, J.D. (2007). Intense hurricane activity over the past 5,000 years controlled by El Ni–o and the West African monsoon. Nature. 447, p. 465-468.
Lodge, D.J.; McDowell, W.H. (1991). Summary of Ecosystem-Level Effects of Caribbean Hurricanes. Biotropica. 23(4a), p. 373-378.
Lugo, A.E. (2000). Effects and outcomes of Caribbean hurricanes in a climate change scenario. The Science of the Total Environment. 262, p. 243-251.
Mallin, M.A.; Posey, M.H.; Shank, G.C.; McIver, M.R.; Ensign, S.H.; Alphin, T.D. (1999). Hurricane Effects on Water Quality and Benthos in the Cape Fear Watershed: Natural and Anthropogenic Impacts. Ecological Applications. 9(1), p. 350-362.
Pielke, R.A.; Rubiera, J.; Landsea, C.; Fernandez, M.L.; Klein, R. (2003). Hurricane Vulnerability in Latin America and the Caribbean: Normalized Damage and Loss Potentials. Natural Hazards Review. 4(3), p. 101-114.
Roth, L.C. (1992). Hurricanes and Mangrove Regeneration: Effects of Hurricane Joan, October 1988, on the Vegetation of Isla del Venado, Bluefields, Nicaragua. Biotropica. 24(3), p. 375-384.
Tanner, E.V.J.; Kapos, V.; Healey, J.R. (1991). Hurricane Effects on Forest Ecosystems in the Caribbean. Biotropca. 23(4a), p. 513-521.
Trenberth, K. (2009). Uncertainty in Hurricanes and Global Warming. Science. 308, p. 1753-1754.
Zimmerman, J.K.; Willig, M.R.; Walker, L.R.; Silver, W.L. (1996). Introduction: Disturbance and Caribbean Ecosystems. Biotropica. 28(4), p. 414-423.
Next Article
Previous Article
Return to Topic Menu
DOWNLOAD the Paper Posting HTML Formating HELP SHEET!
We also have a GUIDE for depositing articles, images, data, etc in your research folders.
Article complete. Click HERE to return to the Pre-Course Presentation Outline and Paper Posting Menu. Or, you can return to the course syllabus
WEATHER & EARTH SCIENCE RESOURCES |
|
OTHER ACADEMIC COURSES, STUDENT RESEARCH, OTHER STUFF
|
|
TEACHING TOOLS & OTHER STUFF
 |
It is 11:45:19 AM on Monday, November 23, 2009. Last Update: Sunday, May 17, 2009
Listen to a "Voice Navigation" Intro!
(Quicktime or