Low-pressure systems that originate over warm tropical waters are known as tropical cyclones. When the sea surface temperature is over 26.5°C, tropical cyclones form. Tropical cyclones can last for days, even weeks, and their courses can be highly irregular. When a cyclone passes over land or over cooler oceans, it dissipates. This article will explain to you about Tropical Cyclones which will be helpful in preparing Geography for the UPSC Civil service exam.

Cyclones

• Cyclones are a type of low-pressure environment with rapid inward air circulation.
• In the Northern Hemisphere, air flows counterclockwise, 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 Paddington invented the term because tropical storms in the Bay of Bengal and the Arabian Sea resemble coiled sea serpents.

Tropical Cyclones - Concept

• The term 'Tropical Cyclone' is used by the World Meteorological Organization to describe weather 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.
• 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.

Favorable Conditions for the Formation of Tropical Cyclone

• A large area of water surface with a temperature above 27° C.
• The Coriolis force is strong enough to form a cyclonic vortex.
• Variations in the vertical wind speed are minor.
• A weak low-pressure area or low-level cyclonic circulation already exists.
• Above the sea level system, there should be a higher divergence.

Origin of Tropical Cyclones

• Tropical cyclones arise over tropical oceans in late summers and have a thermal origin (August to mid-November).
• Because of the Coriolis effect, the powerful local convectional currents take on a whirling motion at these regions.
• These cyclones form and move until they reach a weak place in the trade wind belt.

Developmental Stages of Tropical Cyclone

Tropical cyclones can be classified into three stages throughout their development:

1. Formation and Initial Development Stage

• The transport of water vapor 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.

2. Mature Stage

• 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, the air warms up due to compression, resulting in a warm 'Eye' (low-pressure center).
• A mature tropical cyclone in the Indian Ocean has a concentric pattern of highly turbulent large cumulus thundercloud bands as its principal physical feature.

3. Modification and Decay

• 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.

Structure of a tropical cyclone

1. Eye:

• The "eye" is a roughly circular area at the center of a severe tropical cyclone with comparatively mild winds and favorable weather.
• There is little to no precipitation, and blue sky or stars can be seen on occasion.
• The eye is the area with the lowest surface pressure and the warmest temperatures aloft (in the higher levels) — the eye temperature can be 10°C or warmer than the surrounding environment at a height of 12 km, but only 0-2°C warmer near the surface in a tropical cyclone.
• Eyes vary in size from 8 kilometers to over 200 kilometers across, but the majority are between 30 and 60 kilometers in diameter.

2. Eyewall:

• The "eyewall," a roughly circular ring of deep convection that surrounds the eye and is the area of the tropical cyclone with the strongest surface winds, surrounds the eye. The greatest sustained winds, or the fastest winds in a cyclone, also occur along the eyewall region.
• The eye is made up of sinking air, and the eyewall has a net upward flow due to numerous moderate – and occasionally powerful – updrafts and downdrafts.
• The heated temperatures of the eye are caused by compressional (adiabatic) warming of the subsiding air.
• The majority of soundings taken within the eye reveal a low-level layer that is quite moist, with an inversion above
• It's possible that the sinking in the eye does not reach the ocean surface, but only reaches a depth of 1-3 kilometers.

3. Spiral Bands:

• The eyewall convection is another feature of tropical cyclones that is likely to play a role in the formation and maintenance of the eye.
• Tropical storm convection is arranged into long, thin rain bands that face the same direction as the horizontal wind.
• Spiral bands are so named because they appear to spiral into the core of a tropical storm.
• Low-level convergence is at its maximum along with these bands, so upper-level divergence is most evident above.
• Warm, moist air converges at the surface, ascends through these bands, diverges aloft, and descends on both sides of the bands, forming a direct circulation.
• On the outside of the rain band, subsidence is spread out across a large area, but it is concentrated in the small interior.
• As the air cools, adiabatic warming occurs, and the air becomes dryer.
• Because subsidence is focused on the inside of the band, adiabatic warming is stronger inward from the band, generating a significant disparity in pressure drop across the band.
• Because of the greater pressure gradient on the inside, the tangential winds around the tropical cyclone get stronger. The ring eventually travels toward the center and encircles it, forming the eye and eyewall.
• Thus, the cloud-free eye could be owing to a mix of dynamically forced mass centrifugation out of the eye into the eyewall and a forced descent generated by the eye wall's moist convection.

Vertical Structure of a Tropical Cyclone

The vertical structure of tropical cyclones is divided into three sections.

1. The lowest layer, known as the inflow layer, extends up to 3 km and is crucial for generating the storm.
2. The primary cyclonic storm occurs in the middle layer, which extends from 3 km to 7 km.
3. The outflow layer is located above 7 kilometers. At 12 kilometers and higher, the highest outflow is found. The air moves in an anticyclonic pattern.

Favorite Breeding Grounds for Tropical Cyclones

• South-east Caribbean region ( called hurricanes).
• Philippines islands, eastern China (called typhoons).
• Bay of Bengal and Arabian Sea (called cyclones).
• Around the south-east African coast and Madagascar-Mauritius islands.
• North-west Australia.

Local Names of Tropical Cyclone

In different areas, cyclones are referred to by different names.

1. Hurricanes – In the Atlantic and Eastern Pacific.
2. Typhoons – In Southeast Asia
3. Cyclone – In the Indian Ocean and Western Pacific around Australia.

Characteristics of Temperate Cyclones

1. Size and Shape:

• Tropical cyclones have symmetrical elliptical morphologies with strong pressure gradients (2:3 length-to-breadth ratio).
• They are small—80 km in the center—but can grow to be 300 km to 1500 km in size.

2. Wind Velocity And Strength:

• On a tropical cyclone, wind velocity is higher in the poleward borders than in the center, and it is higher over oceans than over land masses that are separated by physical barriers.
• The wind speed might be anything between 0 and 1200 km/h.

3. Path:

• These cyclones move westward at first but then shift northward about 20 degrees latitude. Around 25° latitude, they shift north-eastwards, then eastwards around 30° latitude. They then deplete their energy and fade away.
• Tropical cyclones travel in a parabolic pattern, with their axis parallel to the isobars.
• A tropical cyclone's path is influenced by the Coriolis force, the earth's rotation, and easterly and westerly winds.
• Tropical cyclones die in 30 degrees latitude due to chilly ocean waters and increased wind shear from westerly winds.

Warning of Tropical Cyclone

• The three major factors for detecting any unexpected meteorological occurrences leading to cyclones are a drop in pressure, an increase in wind velocity, and the storm's direction and movement (track).
• In all countries around the world, including the Arctic and Antarctic areas, a network of weather stations monitors pressure drop and wind velocity.
• The islands take on a unique relevance in this regard since they make it easier to keep track of these processes.
• Detection radars are installed along both coastlines of India.
• Aircraft that carry a variety of instruments, including weather radar, are also used to monitor the situation.
• Satellites monitor cyclones using very high-resolution radiometers that work in the visible and infrared parts of the spectrum (for night vision) to obtain an image of the cloud cover and its structure.
• Radars, aircraft, and satellites use remote sensing to anticipate where the cyclone will strike.

It assists in adopting proactive measures in the following areas:

1. Ports and harbors will be closed.
2. Fishing will be suspended.
3. People will be evacuated.
4. Food and drinking water will be stocked
5. Shelter with sanitation facilities will be provided.

• Today, it is possible to detect a cyclone from the moment it forms on the high seas and track its progress, providing a warning at least 48 hours before it strikes.
• However, storm predictions produced merely 12 hours ahead of time do not have a great degree of accuracy.

Significance of Tropical Cyclone

• Tropical cyclones contribute to global heat balance by transporting warm tropical air from the equator to the poles.
• Without them, the tropics would become much hotter, while the poles would become much colder.
• They are incredibly efficient in producing rain, and hence can be an effective drought reliever.

Conclusion

Though the effects of cyclones on human populations are threatening and devastating, tropical cyclones can also relieve drought conditions. Besides, cyclones are not only observed on Earth but also on planets like Mars, Jupiter, and Neptune.