Title : TROPICAL CYCLONES
Date : Feb 10, 2022
Based on a News Article published in the ‘The Hindu’
Useful for UPSC CSE Prelims and Mains (GS Paper I)
- Cyclones are a type of low-pressure environment with rapid inward air circulation.
- In the Northern Hemisphere, air flows counter clockwise, while in the Southern Hemisphere, it circulates clockwise.
- Storms and poor weather are frequently associated with cyclones.
- The word Cyclone comes from the Greek word Cyclos, which means snake coils. Henry Peddington invented the term because tropical storms in the Bay of Bengal and the Arabian Sea resemble coiled sea serpents.
- Tropical cyclones and Extratropical cyclones are the two types of cyclones (also called Temperate cyclones or middle latitude cyclones or Frontal cyclones or Wave Cyclones).
- The name 'Tropical Cyclone' is used by the World Meteorological Organization to describe meteorological systems with winds greater than 'Gale Force' (minimum of 63 km per hour).
- In the region between the Tropics of Capricorn and Cancer, tropical cyclones form.
- They're large-scale weather systems that form over tropical or subtropical oceans and coalesce into surface wind circulation.
- Though they are known to originate in the Polar Locations, extratropical cyclones can be found in temperate zones and high latitude regions.
- Anticyclones are the polar opposite of cyclones, with outward-spiralling air circulation around a high pressure centre.
- The winds of an anticyclone swirl clockwise in the Northern Hemisphere around a high-pressure area.
- Air enters from above and sinks to the ground in anticyclones. Fair weather is usually associated with high pressure centres.
Cyclones in the Tropics:
- Tropical cyclones are strong storms that form over tropical oceans and then travel inland, wreaking havoc with violent winds, heavy rainfall, and storm surges.
- Tropical cyclones are one of the world's most destructive natural disasters.
- Tropical cyclones form over warm tropical oceans and intensify.
The following are favourable conditions for tropical storm creation and intensification:
- A large area of sea surface with a temperature above 27° C.
- The Coriolis force is present.
- The vertical wind speed varies slightly.
- A weak low-pressure area or low-level-cyclonic circulation that already existed.
- Above the sea level system, there is a higher divergence.
- Tropical Cyclones at Various Stages of Formation
Tropical cyclones can be classified into three stages throughout their development:
- Stages of formation and early development:
- The transport of water vapour and heat from the warm ocean to the overlying air, largely through evaporation from the sea surface, is crucial to the creation and early development of a cyclonic storm.
- Convection with condensation of rising air above the ocean surface stimulates the creation of huge vertical cumulus clouds.
- The air rises in powerful thunderstorms as a tropical storm intensifies, and it tends to spread out horizontally at the tropopause level.
- When air spreads out, a positive pressure is created at high elevations, speeding up the downward migration of air due to convection.
- When subsidence is induced, air warms up due to compression, resulting in a warm 'Eye' (low pressure centre).
- A mature tropical cyclone in the Indian Ocean has a concentric pattern of highly turbulent large cumulus thundercloud bands as its principal physical feature.
- Modification and Decomposition:
- As soon as its source of warm moist air begins to ebb or is abruptly cut off, a tropical cyclone begins to weaken in terms of core low pressure, internal warmth, and extremely fast speeds.
- This occurs after it reaches land or passes across chilly water.
Tropical Cyclone Nomenclature:
- Tropical cyclone naming is a relatively new concept.
- The World Meteorological Organization oversees the process of naming cyclones, which involves various countries in the region (WMO).
- In 2004, a naming system for cyclones in the Indian Ocean region was agreed upon. Bangladesh, India, Maldives, Myanmar, Oman, Pakistan, Sri Lanka, and Thailand are eight countries in the region that each provided a set of names that are assigned in order if a cyclonic storm occurs.
- Cyclones in the Indian Ocean region have names such Hudhud, Titli, Phethai, Fani, Vayu, and Amphan.
Tropical Cyclone Terminology Around the World:
- Typhoons in the China Sea and Pacific Ocean; Hurricanes in the Caribbean Sea and Atlantic Ocean; Tornadoes in the Guinea lands of West Africa and southern USA; Willy-willies in north-western Australia; and Tropical Cyclones in the Indian Ocean are some of the names given to them in different parts of the world.
- Extratropical Cyclone is a type of cyclone that occurs outside of the tropical
- Mid-latitude depressions, temperate cyclones, frontal depressions, and wave cyclones are all names for extratropical cyclones.
- In both hemispheres, these are active above the mid-latitudinal zone between 35° and 65° latitude. The movement is from west to east, and it is most noticeable during the winter months. Polar and tropical air masses collide in these latitude zones, forming fronts.
Extratropical Cyclones Forming:
- The Polar Front theory best explains the formation and evolution of temperate cyclones.
- According to this idea, a polar front is generated when warm-humid air masses from the tropics collide with dry-cold air masses from the poles.
- Because the cold air mass is denser and heavier, the warm air mass is pushed up.
- The contact of cold and warm air masses causes instability, resulting in a drop in pressure at the intersection, particularly in the centre of the interactions.
- As a result of the reduced pressure, a void is generated. The surrounding air rushed in to fill the void, and a cyclone developed as a result of the earth's rotation.
- Extratropical cyclones contrast with the more violent tropics cyclones or hurricanes, which occur in generally constant temperature zones.
Mass of Air:
- At any given height, an Air Mass is a very large volume of air with equal temperature and moisture content (humidity) attributes.
- It has the potential to cover hundreds of thousands of square miles.
- It may have only minor horizontal temperature and moisture variations across the air mass.
- When an air mass stays over a homogeneous area for a long enough period of time, it takes on the features of the area. The enormous ocean surface or vast plains might be homogeneous zones.
- The boundary zone between two different air masses (with markedly different qualities) is called a front.
There are four different kinds of fronts:
- Frontal stationery: A stagnant front occurs when the front of the vehicle remains immobile.
- The contact zone formed by cold air moving towards a warm air mass is known as the cold front.
- Warm front: A warm front is formed when a warm air mass flows towards a cold air mass.
- Occluded front: The occluded front occurs when an air mass is totally raised above the earth surface.
- The fronts occur in the middle latitudes and are marked by a steep temperature and pressure gradient. They generate dramatic temperature changes and make the air to rise, forming clouds and precipitation.
- The Bay of Bengal, the Arabian Sea, and the Indian Ocean are all hotspots for tropical cyclones.
- The Indian coastal states of Tamil Nadu, Andhra Pradesh, West Bengal, Odisha, and Gujarat were battered by tropical storms with significant wind speeds and heavy rainfall (These five states are more vulnerable to cyclone disasters than others in India).
- Because of the strong wind speeds and copious rain that accompany them, the majority of these cyclones are quite destructive.
Cyclones are related with three elements that inflict destruction during their occurrence. These are the following:
- Squalls/strong winds: It causes damage to installations, residences, communications infrastructure, trees, and other structures, resulting in death and property loss.
- Inland flooding and torrential rains: Rain is a major issue for those who have lost their shelter as a result of the cyclone. Heavy rainfall is frequently dispersed across a considerable area, resulting in large-scale soil erosion and embankment deterioration.
- Storm Surge: A powerful tropical cyclone causes an abnormal rise in sea level along the coast.
- Storm surge inundates low-lying coastal areas, killing people and cattle, eroding beaches and embankments, destroying vegetation, and reducing soil fertility.
The Control of Cyclones:
- There are numerous structural and non-structural methods that can be used to effectively handle cyclone disasters.
- Construction of cyclone shelters, cyclone-resistant buildings, road links, culverts, bridges, canals, drains, saline embankments, surface water tanks, communication and power transmission networks, and other structural measures are among the structural measures.
- Non-structural measures such as early warning dissemination systems, coastal zone management, catastrophe risk management, and capacity building of all players involved.
- Under the National Cyclone Risk Mitigation Project (NCRMP), which is being implemented with World Bank assistance, these measures are being adopted and addressed on a state-by-state basis.
Disturbance in the West:
- In India, Western Disturbance is a common weather phenomenon.
- A western disturbance is an extratropical storm that originates in the Mediterranean region and sends heavy winter rain to the Indian subcontinent's north western regions.
- They are responsible for the majority of winter and pre-monsoon rainfall in North-West India (such as Punjab, Haryana, Delhi and western Uttar Pradesh). Cloudy skies, warmer night temperatures, and unexpected rain are frequently linked with this event.
- This precipitation throughout the winter season is critical for agriculture, especially rabi crops like wheat.
- It is believed that western disturbances account for about 5-10% of India's total yearly rainfall.
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