Dissertation Chapter Sample on Tropical Cyclones

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October 31, 2013

Seasonal Prediction of Tropical Cyclones in Australia Region Using Regression

1. Literature Review

1.1 Tropical Cyclone

A tropical cyclone as globally defined is a fast-spinning storm system characterize by a center that has low pressure, powerful winds, as well as a spiral placement of thunderstorms that lead to torrential rainfall. A typical cyclone forms over a water body that is large, for example, seas and oceans-and these large water bodies are relatively warm. These cyclones are known to source their energy from the water that evaporates on the surface of the ocean. This is the water that evaporates condenses and forms clouds and rain. The energy that they source from the evaporation of water differs depending on the geographical location. For example, the mid-latitude cyclonic storms source its energy from the contrasts in horizontal temperature and examples of these mid-latitude cyclonic storms are nor’easters, as well as European windstorms. A tropical cyclone is characterized by winds that are strong and rotating, and as meteorologically explained, these results from conservation of angular momentum. This momentum is brought about by the rotation of the earth that causes the air to flow inwards towards the rotating axis. Because of this, the angle between the cyclone and the earth’s equator is more than 5o that is they do hardly form within this angle. In addition, the typical diameter of a tropical cyclone ranges 100 and 4000km.

As the name suggests, tropical cyclones occur within the geographical regions of these systems. For this case, they form over oceans that fall within the tropical region. A “cyclone” has winds that blow in an anti-clockwise manner in the hemisphere in the Northern part of the globe. On the converse, its winds blow in a clockwise pattern in the hemisphere that falls in the south. The reason for the opposite direction in the flow of winds is the fact that there exists a force known as Coriolis force. The names given to these tropical cyclones are different and the name depends on the location of the cyclone, as well as its strength. The names that are given to these are listed below:

1. Hurricane

A hurricane is characterized by a speed of 74 miles per hour and even more and the eye of this type of storm has a width of twenty to thirty miles. In addition to this, a hurricane covers an area of up to four hundred miles. This cyclone comes with rains that are torrential, high winds, and surging storms. The length at which a hurricane can last is up to two weeks and takes a path that will run across the whole length of the seaboard on the east.

For a hurricane to happen the following characteristics must be present:

i) The systems should be of low pressure
ii) The temperatures over the ocean should be warm
iii) There should be precipitation; the environment around should be moist
iv) The wind patterns over the equator should be tropical in type

2. Typhoon

This type of tropical cyclone is considered mature, and it most commonly forms on the Pacific Ocean in the Northwestern side in an area most commonly known as the northwestern Pacific basin. A typhoon forms between 180o and 100oE.

For a typhoon to happen, the following conditions must be present:

i) The temperatures over the water should be warm
ii) The winds should be spiraling inwards
iii) The environment should be moist

3. Tropical Storm

This is a storm that is intense, has very low pressure, and winds that swirl. In most of the cases, it develops over the tropics. This type of storm can result in winds that cause damage and very heavy rains in the areas that they pass through. In as much as they are not as strong as hurricanes, they can still cause massive destruction; destroy property and even cause death
For a tropical storm to happen the following conditions must be present:

i) The temperature of the ocean water must be more than 26.5oC
ii) The area that has low pressure should experience atmospheric disturbance
iii) The winds that pass over should be low and vertical. This means that the winds that happen at the different altitudes should have a consistent speed.

4. Cyclonic Storm

A cyclone rotates in the same direction as the rotation of the earth. This storm is characterized by winds that are spiraling and their direction depends on whether they are in the northern hemisphere or southern hemisphere. The cyclonic storm that happens in the northern hemisphere has it winds rotating in an in a clockwise direction and those in the southern hemisphere rotate in an anticlockwise direction.

The following conditions must be there for a cyclonic storm to happen:

i) The areas should have low pressure
ii) The area should not be close to the sea in an angle of less than 5o
iii) The surface temperature of the sea should be warm; hence, it should be more than 26oC

5. Tropical Depression

This is a tropical cyclone wind speeds of about 63 kilometers per hour.

The names discussed above are some of those given to tropical cyclones depending on the strength of the cyclone. They all differ in characteristics, as well as conditions that must be present for them to occur.

1.2 El Nino Southern Oscillation ENSO

El Niño, according to the free online dictionary is defined as “a warm ocean current of variable intensity that develops after late December. This happens along the coast of Ecuador and Peru and sometimes causes catastrophic weather conditions.” The El Nino-Southern Oscillation (ENSO) is a phase characterized by temperature variations on the surface of the Pacific Ocean in the Eastern side. Additionally, it is characterized by variations in the pressure of the air surface in the Western Pacific in the tropical region. There are two variations: one is the warm phase. This El Niño has gone along with air pressure that is high, which is in the western Pacific. The second is known as the cold phase, also referred to as La Niña that goes along with air pressure that is low in western Pacific. This climate patterns result in extreme weather exemplified by floods, as well as droughts in many areas across the globe. The countries that are classified as developing and border the Pacific Ocean depending heavily on agriculture. Unfortunately, such countries bear the full brunt of this phenomenon. Looking deeper into the meaning, El Niño translated to English from Spanish is “the Child.” This is because periodic warming that happened in the Pacific is usually realized around Christmas.

El Niño is characterized by a very long period of warming in the areas around the Pacific region where the sea surface temperatures are warmer as compared to the average temperature. The temperatures are at 0.5oC when the temperatures along the east central on the Pacific Ocean. The temperatures are known to happen in a period of between 2-7 years and the go on for a period of nine months to about two years. Statistically averaged, the period of lasting is about five years. The periods are named according to the length of the warming; between periods of 7-9 months, they have been named as El Niño “conditions.” In case they are prolonged for a period that is longer than seven to nine months, they are known as “episodes” of El Niño. In the same way, that El Niño is defined so are the periods of La Niña.

Just like any other condition, El Niño comes with signs. Hence, through this, one is able to know that the El Niño periods are about to begin. The signs are as follows:

a. There is a rise in the pressure of air that is in areas that are around the Indian Ocean, Australia, as well as Indonesia
b. The air pressure over Tahiti, other areas that are in the Central, as well as eastern region of the Pacific Ocean falls
c. The winds, commonly known as trade winds, that are in the south Pacific start to head east or weaken
d. Rains occur in the northern part of the Peruvian Desert as a result of rising of warm air in the areas near Peru
e. The warm water spreads across the east Pacific from the Indian Ocean, as well as the West Pacific.

El Niño has an impact on the nutrients of the water it affects. The warm water is characterized by poor nutrients because it is heated as it passes through the passage towards the east by the Equatorial Current. As this water flows towards the east, it replaces the cold water that is sated with nutrients. When these conditions go on for an extensive period, say months and even years, they cause the easterly trade winds to reduce. As a result, this affects the nutrient-rich water that is cold in that there is no upwelling of the water. The impact that this has on the economy of the local fishing industry as well as the international one is huge.

1.3 An Overview of Methods Used To Predict Tropical Cyclone

There are methods that have been put in place to predict the next occurrence of a tropical cyclone. These methods are important, and without them, it is risky for humanity, at large. This is because it is risky to stay without knowledge and unprepared for the events that happen. There are elements used in forecasting of tropical cyclones and these are:

1.3.1 Track Forecasting

This is the best tool to find the direction, as well as speed is the deep-layer-mean flow. In track forecasting the tool that is used to determine the motion of the tropical cyclone is the large-scale synoptic flow. In a case where there is significant shearing of storms, the best tool to use is the lower-level wind. If there is prior knowledge to the beta effect, it will be easy to steer tropical storms. This is because it helps the tropical cyclones to head in the northwest direction towards the Northern hemisphere…”

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