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A Few More Terms to Know

Major hurricane, a term utilized by the National Hurricane Center, is for hurricanes that reach maximum sustained 1-minute surface winds of at least 111 mph, which is the equivalent of category 3, 4 and 5 on the Saffir-Simpson scale. Intense Hurricane is sometimes also used in scientific literature, but it is an unofficial term.

The structure of the Hurricane consists of the eye, the eye wall, and spiral rain bands. The eye is the most commonly used icon when talking about hurricanes because it looks like an eye.

Hurricanes have a full life cycle that can last for a matter of weeks from Birth-Life-Death. They first begin as a cluster of thunderstorms over warm tropical waters. The breakdown into single cell, multicell, and supercell covers the major storm types within the spectrum. One "cell" denotes one updraft/downdraft couplet. Thus, there are several updrafts and downdrafts in close proximity with a multicell storm. Multicell storms can be broken down further into the categories of multicell line and multicell cluster storms. The "intense" updraft storm is almost invariably the supercell, a storm capable of producing the most devastating weather, including violent tornadoes.

When tropical depressions wind speeds reach 39mph they are given names. Starting in the beginning of the season with A and going to Z if there are more than 26 hurricanes within a season, Greek numbers are then adopted. In 1979 a six-year rotating list of Atlantic storm names was elected to alternate between female and male names. Names are retired if there is substantial damage or other special reasons. Such in the case of Hurricane Katrina… there will never be another Katrina due to insurmountable damage that occurred.

In most parts of the world the Saffir-Simpson Hurricane Scale is used to measure the severity of the storms. The scale is from 1-5 with 5 being the worst possible category. The numbers refer to the estimated property damage, flooding, rain fall and wind speed.

Recent hurricanes like Katrina received more notoriety, because of all the drama surrounding FEMA and the nations slow reaction to the disaster. This does not mean that hurricanes are getting worse than they have been in the past. The majority of tropical hurricanes today are hitting places that have always been plagued with hurricanes. Bhola was the most deadly hurricane of all time, killing somewhere between three hundred thousand and one million people. Hurricanes today are more costly because our culture is much more advanced. The most costly hurricane in history was Katrina, causing 81.2 billion dollars in damages.

Hurricanes are also called typhoons or cyclones depending on where they occur. Worldwide about 96 tropical cyclones occur a year and 12% of those occur in the Atlantic Ocean. About 25 typhoons occur each year in the Western North Pacific Ocean. The Indian Ocean also has a high cyclone activity. The Indian Ocean has high activity because thunderstorms develop due to the warm Indian Ocean and the nearby InterTropical Convergence Zone (ITCZ), which is a ring of thunderstorms that surrounds the globe in the tropics. Hurricanes are more severe over water and get weakened as they travel over land. Hurricanes develop over large bodies of warm water; they lose some strength when they travel over land. The severity of hurricanes can be affected by their location due to El Nino and West African Monsoons. Hurricanes that do hit land can cause storm surges. These cause more flooding depending on where mouths of rivers are located and what direction the hurricane is rotating. Storm surges can build up to heights ranging from 3 to 30 feet. The Southwest United States is quite flat and therefore especially vulnerable to flooding and storm surges. Most hurricanes occur on the Intertropical Front (ITF), the Intertropical Convergence Zone (ITCZ) or the monsoon trough. The Intertropical Front or ITF is the meeting point of air brought by the trade winds from the circulation of winds from both the northern and southern hemispheres. The Intertropical Convergence Zone or ITCZ is the area encircling the equator where winds from the northern and southern hemispheres come together. Where the ITCZ merges with a monsoonal circulation, it is called a monsoon trough. Monsoon trough’s are common in Australia and parts of Asia. These three weather system areas are the cause of most of the world’s hurricanes.

They produce strong winds, high waves, torrential rain, floodwaters, and sometimes they spawn tornadoes. Hurricanes affect the costal environment the most. Floodwaters can reach as for as 25 miles inland. The storms can carry much heat and energy inland causing atmospheric circulation. Storm surges, strong winds, flooding, tornadoes and rip tides can cause a massive amount of environmental destruction after the hurricane has calmed down. Heavy rain and flooding has a major affect on the environment after the storm. Standing water can cause disease and transportation routes may have been destroyed. Rescue efforts can be cut off due to breakdowns in communications infrastructure. They can be beneficial to dry areas, because they bring great amounts of rain. They also move heat from the tropics pole ward. Sand is eroded from beaches and coral can be rearranged. Hurricanes can strip trees and scatter forest debris, which makes great fuel for wild fires. A great example of this was hurricane Gilbert created an environment for a forest fire, which burned for three months and destroyed 460 square miles of forest.

These all emit high levels of greenhouse gases within the atmosphere; CO2 being the main gas. Also, believe it or not, cows in large numbers can be harmful on the environment. They release high amounts of methane gas, another greenhouse gas, into the atmosphere. The large amount of gases released from volcanic eruptions, along with deforestation, pollution, and potentially water vapor released from industrial smoke stacks all do their share in releasing greenhouse gases into the atmosphere and contributing to global warming.

Today, long gone are the days when brutal ocean storms would hit with only hours warning to flee; hurricane trackers use a wide variety of modern technology combining years of weather research with computer science. Since 1943, aircrafts make routine flights about the coasts and oceans to get a clear bird’s eye view of the sea and see any bad weather patterns heading towards the coast. Satellite imaging that has been used since the 1960’s. The NOAA's National Environmental has two types of satellites: geostationary operational environmental satellites (GOES) for national, regional, and short-range forecasting and polar-orbiting operational environmental satellites (POES) for global, long-term forecasting and environmental monitoring. Together these two types of satellite imaging complete a “global weather satellite monitoring system”, tracking varying temperatures and providing atmospheric data and cloud images needed to track and understand hurricanes. With this comes the use of the Doppler radar, which reads precipitation levels and shifting patterns, along with a wind data across the atmosphere, providing forecasters with an important profile analysis of a storm. Also, buoys and floats are placed throughout the ocean to measure air and wind temperatures, wave and wind height, speed and direction. Scientist combine all of the data gathered by all of the previous mentioned methods to create computer forecast models, which evaluates of the gathered data to calculate future weather patterns. Hurricane predictions in the end fall into two categories, “seasonal probabilities and tracking the path of a current hurricane,” Seasonal predicted hurricanes are based off of past data and number of hurricanes. Every April scientists begin to predict how many hurricanes will occur and their intensity based off of this data.

http://celebrating200years.noaa.gov/magazine/devast_hurricane/welcome.html#fore

Hurricanes form over warm bodies of water, due to evaporation of the seawater. The evaporated seawater is absorbed into the air making it moist. This moist air rises and it lowers the atmospheric pressure of the air beneath it. Where there is low atmospheric pressure the air between the water and the top of the atmosphere is less dense, and therefore weighs less. Like most things in the world, air moves from areas of high pressure to areas of low pressure this creates wind. The warmer the temperature of the water, the more evaporation, and the more moist the air. This causes a lower atmospheric pressure and thus stronger winds.

Development of a hurricane also depends on the wind shear. Wind shear is the difference in direction and speed between winds at upper and lower elevations. Hurricanes develop best when there is little wind shear because this allows the warm inner core of the storm to stay intact. If there is higher wind shear than this could cause the speed of the wind at different elevations to be different, which could break up the storm. The storm would also be affected if the directions at the elevations were different because it could cause the storm to tip over or for the two to split.

The first step in hurricane formation is tropical disturbance where the rain clouds are building because of the moist air rising and cooling. Warm air can hold more water vapor than cool air so when the warm moist air cools the water changes to droplets of water that form clouds. Some of these clouds may become cumulonimbus clouds that produce heavy rains and thunderstorms. If the tropical disturbance has a lot of heat energy and moisture, than the cumulonimbus clouds will remain for longer this is because the warm moist air from the surface is attracted to low pressure.

Hurricanes continue to grow due to the fact that warm moist air is attracted to low pressure. This causes the winds to increase in speed. A hurricane tends to last for 3 to 14 days and travels at about 10 to 20 mph. Hurricanes in the Northern Hemisphere travel east to west, but as they approach the coast they shift north. In the Southern Hemisphere hurricanes travel westward, then turn southwest, south, and then finally southeast. Although most hurricanes follow these patterns the path of a hurricane is difficult to predict, but all move away from the equator to higher latitudes.

At higher latitudes the air is colder which means there is less moisture in the air. These conditions along with greater wind shears weaken the hurricane because it does not have the warm moist air supplying it. When a hurricane goes over land than it quick loses its supply of energy from the warm moist air from the water.

The environment can affect hurricanes by not only increasing the sea surface temperatures but also other factors can influence hurricane activity. In the past decade the high-pressure ridge in the troposphere across the central and eastern North Atlantic has increased, this also increases the hurricane activity. The African easterly lower atmospheric winds have also increase and these winds increase the development of hurricanes that move westward from the African Coast. The increase of these two things could be another reason why hurricane activity has increased, but the cause for their increase was not found.

Hurricane activity has increased as shown by data from the National Oceanic and Atmospheric Administration (NOAA). From 1995-2004 has been an increase in the number of intense hurricanes. The question is whether this is due to global warming or has another possible cause.

Many researchers are looking into whether hurricanes can be affected by global climate change and if this will increase the number and intensity of hurricanes. Global warming has been a focus of many studies because it could increase the sea surface temperatures in tropical waters. Hurricanes are formed in the summer and early fall months in the northern hemisphere when temperatures are warmer. Things that can cause hurricanes are high humidity, light winds, and warm sea surface temperatures (80°F). Therefore an increase in temperatures from global warming is something that does need to be examined.

NASA has presented models on how global warming can change the intensity of hurricanes. They say that if ocean temperatures increase by 2-2.5°C the intensity of hurricanes would increase by 6-10%. Just from 1970, the average ocean temperature has increased by half a degree. Other scientists have reported on the positive correlation on the warmer sea surface temperatures and the increase in the number of intense storms. In 2005 and 2006 there was an increase in the number of category 4 and 5 storms. Also when sea surface temperatures increase the number of cyclones increase.

Warmer sea surface temperatures cause more moisture to evaporate and if this is enough it will trigger thunderstorms, which may become tropical storms and hurricanes. Researchers have found that water vapor levels have increased 15% on average in the last 30 years in the Atlantic hurricane zone. This increase results in more category 4 and 5 hurricanes.

The affects of global warming could not just increase the intensity of hurricanes but they also may create hurricanes in parts that have never before seen hurricanes. For example, In 2004, Brazil was struck with its first hurricane ever recorded. Also in 2003, Hurricane Juan struck the coast of Canada.

Another theory for this change in hurricane activity has been reported that excludes global warming as a cause. It is the Atlantic multi-decadal oscillation (AMO) that says the Atlantic has a natural cycle of 20-40 years where there are periods of increased activity and then decreased activity. The AMO is characterized by changes in the sea surface temperatures. Since the mid 1990s we have been in the warm phase. Some evidence for this theory is that during the 1950s and 1960s there were more intense hurricanes during the warm phase, but for two decades following the hurricane activity decreased. In the mid 1990s hurricane intensity increased once again and it is still at an increased level. The arguments against this theory are that measurements have changed and are more advanced since the 1970s. Also in the 1970s and 1980s there was an increase in aerosols which could have caused a cooling, but the global warming from the 1990s overcame the aerosol cooling.

Researchers with the Woods Hole Oceanographic Institution (WHOI) conducted a study looking at the hurricane activity in the Atlantic for the last 5,000 years by using sedimentation data. They found that there were long stretches of increased activity and then stretches of decreased activity that goes along with the AMO. They also found that the number of intense hurricanes increased when the El Niño was weak and when the West African monsoon was strong. The West African monsoons can affect hurricane activity because they provide the seedlings for hurricane development because the storms lead to easterly atmospheric waves moving across the Atlantic.

The research on this subject is continuing and many different ideas have come forth. It is important to note that while they are using past records for analysis, all predictions are based on models rather than actual experiments which is probably why there are many conflicting views. Bender et al. recently reported in Science that global warming would have too effects on the activity of hurricanes. The number of hurricanes would decrease, but for the hurricanes that are formed they would be more intense. There would be more of the category 4 and 5 hurricanes that cause the most damage. This is based on the fact that increased water vapor will intensify existing storms but will inhibit the formation of new storms. They also state that the largest increase in intensity will be seen in the Western Atlantic, north of 20°N.

http://earthobservatory.nasa.gov/Features/Hurricanes/

http://earthobservatory.nasa.gov/Features/Hurricanes/hurricanes_3.php
http://www.scientificamerican.com/article.cfm?id=stronger-link-found-between-hurricanes-global-warming

http://www.atmos.ucla.edu/~liougst/Lecture/CC-Lab_2.pdf

http://www.ucar.edu/communications/staffnotes/0410/hurricane.html

http://www.whoi.edu/page.do?pid=7545&tid=282&cid=27546&ct=162

Bender, M.A., T.R. Knutson, R. E. Tuleya, J. J. Sirutis, F. A. Vecchi, S. T. Garner, I.S. Held. Jan 22,2010 “Modeled impact of Anthropogenic warming on the Frequency of Intense Atlantic Hurricanes” Science
Kerr, Richard Jan 22, 2010 Science review article “Models Foresee More-Intense Hurricanes in the Greenhouse”
What is the Atlantic Multi-decadal Oscillation?

The Atlantic Multi-decadal Oscillation (AMO) is a 20-40 year cycle that occurs in the North Atlantic Ocean. It causes long-duration change in the sea surface temperature. From the extreme cool and warm phase, the different in sea surface temperature is about 1° F. The area affected by the AMO is in the Atlantic between the equator and Greenland, although some areas in the North Pacific can also be affected. Currently, we have been in the warm phase since the mid 1990s.

AMO not only causes severe Atlantic hurricanes, but it also affects air temperatures, rainfall over much of the Northern Hemisphere, the frequency of droughts in North America, and it also over exaggerates human-induced global warming. A warm AMO will cause there to be more frequent and/or severe droughts in the Midwest and Southwest of North America. The Pacific Northwest and Florida will get more rainfall when there is a positive AMO.

The AMO does not influence the number of weak storms, but it does influence the intensity of the storms. In the warm phase AMO causes there to be more intense hurricanes, but does not alter the average number of hurricanes.

The AMO is caused by changes in the south to north circulation and the overturning of water and heat in the Atlantic Ocean. The AMO will enter a cool phase when the overturning circulation decreases. Scientists have figured out what causes the AMO and because of this they are able to calculate the probability of a change in the AMO, but they are still unable to predict exactly when the AMO will change. Despite this, just the probability of the change has provided useful information for long-term planning in climate sensitive applications. An example of this is water management where scientists can look at what the region could be facing in the long term future if a change in the AMO occurs. If there was a change in the AMO, the Pacific Northwest would just see increased rainfall, but this method would be better used in the Midwest where they would have droughts.

The AMO is different from the North Atlantic Oscillation (NAO) because the NAO is the changes in the atmospheric pressures.

El Niño causes an increase in ocean surface temperatures near the equator in the East Pacific Ocean. Normally during an El Niño there is an increase in hurricane activity in the eastern Pacific but a decrease in activity in the Atlantic, Gulf of Mexico, and the Caribbean Sea. NASA reports that the probable cause of this difference is how El Niño affects the wind shears. Wind shears is a change of direction and/or speed of wind and increased vertical wind shear helps prevent hurricanes from developing from tropical disturbances. The increased vertical wind shear happens in the Caribbean and the Atlantic, while a reduced wind shear is present in the eastern Pacific.

Currently there are some cyclones present in the South Pacific Basin. Cyclone Oli was generated on February 1, and has reached a category 4 cyclone according to the Saffir-Simpson scale. Cyclone Pat is also in the South Pacific Basin but has only reached a category 2 cyclone. Cyclone Rene has reached a category 3 cyclone. In the South Indian Basin, cyclone Gelane has reached a category 1 cyclone.

H>E – The sea surface temperature reaches 80°F and a hurricane can form.

H>A – The warm seawater evaporates producing warm moist air.

H>A>E – The warm moist air cools and lowers the atmospheric pressure providing conditions for hurricanes to form.

E>H>A – The hurricane is fueled by the warm moist air that warm seawater produces.

E>A – Hurricanes can cause tornadoes to form.

E>H – Hurricanes can cause storm surges.

E>H – Water can be brought inland by hurricanes.

E>H>L – The water from a hurricane can cause flooding and mudslides.

E>H>L>B – The flooding can contaminate the water supply and can spread disease.

E>L>B – The Hurricanes can strip trees and scatter the forest debris which makes good conditions for forest fires.

E>L>B>A – The forest fires, if the occur, will not only destroy the plants, but will also put excess CO₂ in the atmosphere.

4. 
   List what is unknown
   

• 
  How exactly do the West African monsoons increase hurricane activity?
  
• 
  Does the AMO affect El Niño frequency?
  
• 
  How are hurricanes able to create such high winds?
  
• 
  How does flooding from hurricanes affect the water supply?
  
• 
  What are common diseases that occur in plants, animals, and humans after hurricanes hit land?
  
• 
  How do hurricanes affect the hydrosphere? Do they have a positive or negative affect on marine life?
  
• 
  How does global warming affect sea surface temperature?
  

5. 
   List what needs to be done
   

• 
  Research more on the Atlantic Multi-decadal oscillation.
  
• 
  Research more on West African monsoons.
  
• 
  Look into how global warming affects the sea surface temperatures exactly.
  
• 
  Look into possible affects of the hurricanes on marine life.
  
• 
  If we look at the hurricane activity when the AMO is in a cool phase than the true effect of global warming.
  

6. 
   Develop a problem statement
   

7. 
   Gather information
   

• 
  Tropical cyclones require a water temperature of at least 80°F.
  
• 
  Tropical depressions have speeds below 39 miles per hour, tropical storms have wind speeds between 39 mph and 74 mph, and hurricanes have wind speeds over 74 mph.
  
• 
  Cyclones in the North Atlantic Ocean, Southeast Pacific Ocean, and the Northeast Pacific Ocean are called hurricanes.
  
• 
  Typhoons occur in the Northwest Pacific Ocean
  
• 
  Cyclones in the Indian Ocean and Southwest Pacific Ocean.
  
• 
  Eye of the hurricane can be 30-40 miles wide.
  
• 
  Most dangerous part of a hurricane is the storm surge, which is a dome of ocean water that can be 20 feet high at its peak and 50 to 100 miles wide.
  
• 
  Hurricanes can also cause high winds, debris, tornadoes, and flooding from heavy rains.
  
• 
  Half of the tropical disturbances that develop each year in the Atlantic ocean begin over Africa near the Cape Verde Islands.
  
• 
  The Atlantic hurricane season is between June and November.
  
• 
  Hurricanes in the Northern Hemisphere rotate counterclockwise, those in the Southern Hemisphere rotate clockwise.
  
• 
  The eye is an area of calm where the rest of the storm rotates and has the lowest surface pressure.
  
• 
  The eye wall causes the most damage and intense rainfall.
  
• 
  Hurricanes develop from clusters of thunderstorms over tropical waters.
  
• 
  Goes from tropical disturbance to tropical depression to tropical storm to tropical cyclone.
  
• 
  Tropical depressions are given names once their speeds reach 39 mph. At the beginning of the season the names start with A and make their way to Z after all the letters have been used then Green numbers are used.
  
• 
  In 1979, they began to use male names also.
  
• 
  Hurricanes are categorized using the Saffir-Simpson scale.
  
• 
  The number of category 4 and 5 hurricanes has increased.
  
• 
  Hurricanes can produce tornadoes.
  
• 
  Hurricanes form because the warm moist air rises, which lowers the atmospheric temperature. When the warm moist air rises, it cools which produces clouds and rain.
  
• 
  The continued supply of warm moist air from the ocean supplies heat energy to the developing hurricane.
  
• 
  All hurricanes move to higher latitudes where there is less warm moist air and greater wind shears, this weakens the hurricane. When it moves overland it quickly loses its supply of heat energy and dies.
  
• 
  The African easterly lower atmospheric winds increase the development of hurricanes on the African coast.
  
• 
  Global warming could increase the sea surface temperatures.
  
• 
  Water vapor levels have increased by 15% on average in the last 30 years in the Atlantic hurricane zone.
  
• 
  The increased hurricane activity could be due to the Atlantic multi-decadal oscillation.
  
• 
  There has been an increase in the number of intense hurricanes.
  
• 
  The AMO has been and currently is in the warm phase since the mid 1990s.
  
• 
  El Niño causes an increase in hurricane activity in the Pacific, but a decrease in the Atlantic.
  

8. 
   Present findings
   

Hurricanes can form when sea surface temperatures exceed 80°F because the warm water causes more warm moist air, which leads into hurricanes. The AMO causes the sea surface temperatures to increase, but only by about 1°F. Since it is a small change we believe that is why it does not cause more hurricanes to form, but increases the intensity of already formed hurricanes. This is because the temperature of the water will be warmer which will create more warm moist air which feeds the growing hurricane.