Here is a compilation of essays on ‘Tropical Cyclones’ for class 8, 9, 10, 11 and 12. Find paragraphs, long and short essays on ‘Tropical Cyclones’ especially written for school and college students.
Essay on Tropical Cyclones
Essay # 1. Introduction to Tropical Cyclones:
Cyclones developed in the regions lying between the tropics of Capricorn and Cancer are called tropical cyclones which are not regular and uniform like extratropical or temperate cyclones. There are numerous forms of these cyclones which vary considerably in shape, size, velocity, and weather conditions. The weather conditions of low latitudes mainly rainfall regimes are largely controlled by tropical cyclones.
There is no commonly acceptable viewpoint for the origin of tropical cyclones because the exact mechanism of the formation and development of these cyclones could not be properly understood as yet. According to the advocates of frontal theory all types of cyclones originate because of frontogenesis.
Inspite of the absence of two contrasting air masses in the equatorial region fronts are formed due to meeting of land and sea winds. Initially, different fronts are formed but later they disappear. This frontal concept of the origin of tropical cyclone is no longer acceptable because tropical cyclones in no case are related to fronts.
In fact, tropical cyclone is like a heat engine which is energized by the latent heat of condensation. On an average, tropical cyclones are formed due to development of low pressure of thermal origin.
They develop when the following requirements are fulfilled:
(1) There should be continuous supply of abundant warm and moist air. Without doubt tropical cyclones originate over warm oceans having surface temperature of 27°C during summer season.
(2) Higher value of coriolis force is required for the origin of these cyclones. It is apparent that tropical cyclones are practically absent in a belt of 5°-8° wide on both sides of the equator where coriolis force is minimum. It means that cyclonic circulation of air is caused due to deflection in wind direction resulting from coriolis force. Majority of the tropical cyclones originate within a belt of 5°-20° latitudes in the western parts of the oceans.
(3) They are associated with inter-tropical convergence (ITC) which extends from 5° to 30°N latitudes during summer season.
(4) Pre-existing weak tropical disturbances intensify and ultimately develop into high intensity violent tropical cyclones.
(5) There should be anticylonic circulation at the height of 9000 to 15000m above the surface disturbance. The upper air anticyclonic circulation sucks the air from the ocean surface above and thus the upward movement of air is accelerated and low pressure centre at the surface is further intensified.
(6) Tropical cyclones develop around small atmospheric vortices in the inter-tropical convergence zone (ITC).
Essay # 2. Features of Tropical Cyclone:
They are characterized by the following salient features:
(1) Size of tropical cyclones varies considerably. On an average, their diameters range between 80km and 300km but sometimes they become so small that their diameter is restricted to 50km or even less.
(2) They advance with varying velocities. Weak cyclones move at the speed of about 32km per hour while hurricanes attain the velocity of 180km per hour or more.
(3) Tropical cyclones become more vigorous and move with very high velocity over the oceans but become weak and feeble while moving over land areas and ultimately die out after reaching the interior portion of the continents. This is why these cyclones affect only the coastal areas of the continents (e.g. south and south-east coasts of the USA, Tamil Nadu, Orissa and West Bengal coasts of India, southern coastal regions of Bangladesh etc.).
(4) The centre of the cyclone is characterized by extremely low pressure. Isobars are more or less circular but are fewer in number. This is why winds hurriedly rush up towards the centre and attain gale velocity.
(5) Like temperate cyclones, tropical cyclones are not characterized by temperature variations in their different parts because they do not have different fronts (warm and cold fronts).
(6) There are no different rainfall cells in the tropical cyclones as is the case of temperate cyclones and hence each part of the cyclones yields rainfall.
(7) Tropical cyclones are not always mobile. Sometimes, they become stationary over a particular place for several days and yield heavy rainfall causing flood deluge and environmental disaster.
(8) The tracks of tropical cyclones vary considerably in different parts. Normally, they move from east to west under the influence of trade winds. The general direction is westerly upto 15° latitude from the equator, pole-ward between 15°-30° latitudes, and again westerly. These cyclones weaken when they enter subtropical regions.
(9) Tropical cyclones are confined to a particular period of the year, mainly during summer season. The frequency and affected areas of tropical cyclones are far less than those of the temperate cyclones.
(10) Tropical cyclones become disastrous natural hazards because of their high wind speed of 180 to 400km per hour, high tidal surges, high rainfall intensity (highest recorded rainfall value exceeded 2000mm per day in Philippines), very low atmospheric pressure causing unusually rise in sea-level, and their persistence for several days or say about one week over a particular place.
Essay # 3.
Types of Tropical Cyclones:
It may be pointed out that tropical cyclones are so varied in size, weather conditions and their general characteristics that no two cyclones are identical and therefore it becomes very difficult to classify them into certain categories.
Generally, they are divided into 4 major types:
(1) Tropical disturbances or easterly waves,
(2) Tropical depressions,
(3) Tropical storms, and
(4) Hurricanes or typhoons.
On the basis of intensity they are divided into two principal types and 4 subtypes:
(1) Weak cyclone,
(i) Tropical disturbances,
(ii) Tropical depressions,
(2) Strong and furious cyclones,
(iii) Hurricanes or typhoons, and
(iv) Tornadoes.
(1) Tropical Disturbances:
Tropical disturbances are migratory wavelike cyclones and are associated with easterly trade winds. They are also called easterly waves. Winds move towards centre with low speed. Though they move in westerly direction under the influence of trade winds with low velocity but they are most extensive and widespread and influence the weather conditions of both tropical and subtropical areas. Most of the easterly waves develop between 5° and 20° north latitudes in the western parts of the oceans.
Sometimes, they are so sluggish that they remain stationary over an area for several days. They are associated with heavy cumulus or cumulonimbus clouds which yield moderate to heavy rainfall with thunderstorms. Sometimes, the easterly waves are so greatly intensified that they develop into hurricanes. Generally, they develop in the Caribbean Sea and North Pacific Ocean during summer months.
(2) Tropical Depressions:
Tropical depressions are centres of low pressure surrounded by more than one closed isobars and are very small in size. Wind velocity around low pressure centre ranges between 40-50km per hour. Their direction and velocity are highly variable. Sometimes, they remain stationary at a place for several days. They usually develop in the vicinity of intertropical convergence (ITC) but seldom develop in the trade wind belt.
Tropical depressions generally influence the weather conditions of India and north Australia during summers. After being originated in the Bay of Bengal these cyclones move in northwesterly and westerly directions and reach inner parts of India. Sometimes, they become so strong that they yield heavy downpour resulting into severe floods.
(3) Tropical Storms:
Tropical storms are low pressure centres and are surrounded by closed isobars wherein winds move towards the centre with the velocity ranging between 40 to 120km per hour. They frequently develop in the Bay of Bengal and Arabian Sea during summer season. They also develop in the Caribbean Sea and in the vicinity of Philippines.
Many of these cyclones become violent and disastrous atmospheric hazards as they cause heavy rainfall and thus inundate low-lying areas of Bangladesh, delta region of West Bengal and coastal areas of Orissa, Andhra Pradhes and Tamil Nadu. The northern parts of Bay of Bengal mostly the Ganga Delta plains of West Bengal, India and Bangladesh very often suffer from frequent severe cyclonic storms and resultant storm surges (tidal waves) because of a combination of several natural conditions and phenomena such as astronomical tides, funneling coast configuration, low and flat terrains of coastal areas and frequent occurrence of severe cyclonic storms.
The most disastrous cyclone, which hit the coastal low land of Bangladesh on November 12, 1970, claimed 3,00,000 human lives. Similarly, the deadly cyclone of 1737 claimed the lives of 3,00,000 people in the east coast of India. The disastrous cyclone of 1977 moving with a speed of 175km per hour killed 55,000 people, destroyed the homes of 2,000,000 people and ruined 1,200,000 hectares of agricultural crops and made most of the coastal land barren and wasteland because of deposition of thick layer of salt on the soils by storm surges in Andhra Pradesh.
Super-cyclone of Orissa of 1999 (Oct. 29-31) with wind velocity of more than 300 km per hour killed about 100,000 people (official figure, 10,000), washed out 200 villages, damaged standing crops of 1.75 million hectares and claimed loss of property worth 1,000 billion rupees in the coastal districts.
(4) Hurricanes or Typhoons:
The extensive tropical cyclones surrounded by several closed isobars are called hurricanes in the USA and typhoons in China. They are also called wiliy-willy in Australia, cyclones in Indian Ocean, ‘baguio’ in Philippines, ‘taifu’ in Japan etc. Hurricanes are, in fact, most violent, most awesome, and most disastrous hazards of all the atmospheric disturbances. They move with average speed of more than 120km per hour. Though hurricanes are most extensive and violent but their climatic importance is limited because of their fewer numbers and their occurrence in limited areas.
Though hurricanes and temperate cyclones look similar in appearance but they may be differentiated on the following grounds:
(1) Hurricanes are represented by more symmetrical and circular isobars. Pressure increases sharply from the centre towards the outer margin resulting into steep pressure gradient. This is why hurricanes move with great force and high speed.
(2) The rainfall occurring from hurricanes is in the form of heavy downpour and is widespread and uniformly distributed whereas precipitation from temperate cyclones is confined to only warm and cold fronts. Warm and cold sectors are devoid of precipitation.
(3) There is no temperature variation in hurricanes. They are also not characterized by different types of fronts (warm and cold fronts) and contrasting air masses as is the case with temperate cyclones.
(4) There is no change in wind direction in hurricanes. Winds blow from the outer margin towards the centre and then rise upward.
(5) Hurricanes are not associated with anti-cyclones.
(6) Unlike temperate cyclones they move from east to west.
Besides, hurricanes are characterized by the following properties. The diameters range between 160 and 640km. The size of hurricanes is usually small at their origin points near the equator but the size gradually increases away from the equator. The pressure at the centre ranges between 900 and 950mb which is perhaps the lowest pressure of all the tropical cyclones. The pressure gradient between the centre and outer margin ranges from 10mb to 55mb.
The areas of 6 to 48 sq km around the centre of hurricane is generally dry and rainless and winds are feeble. This is called ‘eye of the cyclone’. The waves caused in the oceans due to ferocity of hurricanes are called hurricane waves which are generally from 3 to 6m in height. These storm surges inundate the coastal areas with immense volume of oceanic water and thus cause immense loss to human health and wealth. Hurricanes extend upto 12,000m above the ocean surface. They last for many days and sometimes for more than a week.
Essay # 4.
Distribution of Tropical Cyclones:
Tropical cyclones mostly develop over the ocean surface between 5°-15 latitudes in both the hemispheres and influence weather of coastal areas of the continents.
There are 6 major regions of the tropical cyclones e.g.:
(1) West Indies, Gulf of Mexico, and Caribbean Sea,
(2) Western North Pacific Ocean including Philippines Islands, China Sea, and Japanese Islands,
(3) Arabian Sea and Bay of Bengal,
(4) Eastern Pacific coastal region off Mexico and Central America,
(5) South Indian Ocean off Madagascar (Malagasi), and
(6) Western South Pacific Ocean, in the region of Samoa and Fiji Island and the east and north coasts of Australia.
North Atlantic Ocean: It may be pointed out that the occurrences of tropical cyclones are rhythemic in nature because they are restricted to a certain season of a year which varies from one region to the other region. On an average, about 7 cyclones develop every year in the southern and south-western parts of the Atlantic Ocean, most of which become hurricanes.
They Develop:
(i) In August and September around Cape Verde Island,
(ii) Between June and October to the north and east of West Indies and to the south of the Atlantic coast of the USA,
(iii) From May to November in the North Caribbean Sea,
(iv) From June to October in the south Caribbean Sea, and
(v) From June to October in the Gulf of Mexico.
North Pacific Ocean:
The cyclones after originating off the western coast of Mexico move northwestward and affect the weather of California. Sometimes, they also reach Hawaii Island. About 5 to 6 tropical cyclones develop each year between June and November and two of them gain hurricane intensity.
South-West North Pacific Ocean:
Normally, tropical cyclones develop in China Sea, off the coasts of Philippines Islands and South Japan between May and December. They have disastrous effects on the eastern coasts of China where they gain the ferocity of typhoons. About 12 typhoons develop every year.
South Pacific Ocean:
Tropical cyclones develop to the east of Society Island (east of 180° longitude) during December-April and influence the weather of north-east coast of Australia.
North Indian Ocean:
After originating in the Arabian Sea and Bay of Bengal tropical cyclones (also called as depressions) influence the weather conditions of India on a large-scale between April and December.
South Indian Ocean:
Cyclones originate off the coasts of Re Union, Madagascar, and Maritius islands between November and April.
Essay # 5. Weather Conditions Associated With Tropical Cyclones:
The arrival of tropical cyclones at a particular place is heralded by sudden increase in air temperature and wind velocity, marked decrease in air pressure, appearance of cirrus or cirrostratus clouds in the sky, and emergence of high waves in the oceans. The clouds are thickened and become cumulonimbus which yield heavy rains. The clouds are also associated with thunder and lightning.
On an average, a single storm yields 100 to 250mm of rainfall but if obstructed by relief barrier it may give as heavy rains as 750 to 1000mm. The visibility becomes zero because the sky is overcast with thick and dark thunder clouds. Such destructive conditions persist for a few hours only.
The arrival of the centre or the eye of the cyclone is characterized by calm breezes, clear sky, rainless fine and settled weather, and low pressure at the centre. Such weather conditions do not persist for more than half an hour.
The weather suddenly changes with the arrival of the rear portion of the cyclone as the sky again becomes overcast, wind direction changes, and pressure sharply goes up. There is heavy downpour with cloud thunder and lightning and storm becomes very severe and furious. This situation persists for several hours. Slowly and slowly the ferocity of cyclone starts declining and the weather becomes calm after the cyclone has passed off. The sea surface also becomes calm and clear weather sets in.