Air Mass, Cyclone and Anti-Cyclone

🌬️ Air Mass

A large body of air uniformly related to temperature and humidity

🌦️ Front

The zone between cold and warm air masses

📂 Types of Fronts

Warm Front

Warm air advances over cold air • Gradual lifting • Steady rainfall

Cold Front

Cold air advances under warm air • Steep lifting • Heavy rainfall

Stationary Front

Neither warm nor cold air advances • Boundary remains stationary

Occluded Front

Cold front catches warm front • Warm air is lifted completely off the ground

📌 Frontogenesis Process of formation of a front

📌 Frontolysis Weakening/dissipation of a front and its horizontal temperature gradient

⚡ Quick Recall

Mid-latitude / Temperate cyclones form due to frontogenesis — front formation is central to their development, unlike tropical cyclones.

🌀 Cyclone → A Low Pressure Zone

Key Feature	Details
Centre	Low pressure
Periphery	High pressure • Wind flows from periphery to centre
Direction	Northern Hemisphere → Anti-clockwise • Southern Hemisphere → Clockwise (Coriolis force)
Eye of the Cyclone	A mature organized tropical cyclone may develop a calmer eye; it is not always rain-free.

✅ Essential Conditions for Tropical Cyclone

Favourable SST: about 26.5°C or warmer over a sufficiently deep warm ocean layer
Coriolis force must be present — absent at the equator → no cyclone at the equator
Low vertical wind shear: little change in wind speed/direction with height
Low pressure area

📌 Absence of cyclones on the Equator Coriolis force value is Zero there

⚠ Exam Trap

Cyclones need Coriolis force to spin, but Coriolis force is zero at the equator — that's exactly why cyclones never form right on the equator, despite warm ocean waters there.

📂 Types of Cyclones

Tropical Cyclone

Between Tropic of Cancer and Tropic of Capricorn
Develops over warm oceans; may move over land and usually weakens without ocean heat supply.
Can be highly destructive; impacts depend on storm intensity, track, size and exposure.
Often initially westward, with possible poleward/eastward recurvature

Temperate / Extra-Tropical Cyclone

Between 35°–65° Latitudes (both hemispheres)
Occurs on both sea and land surface
Can also be highly destructive; no universal lesser-impact rule
Moves West to East

🌍 Different Names of Tropical Cyclones

Region	Name
South China Sea / Western Pacific	Typhoon
Indian Ocean	Cyclone
Australia / Southwest Indian Ocean	Tropical cyclone; ‘willy-willy’ traditionally refers to an Australian dust devil.
USA, Caribbean Islands / Atlantic Ocean	Hurricane

📌 Funnel-shaped destructive storm in USA Tornado

⚠ Exam Trap

Many tropical cyclones initially move westward and may recurve poleward/eastward; mid-latitude cyclones generally move west→east with westerlies.

☀️ Anti-Cyclone → A High Pressure Zone

High-pressure system often favouring settled weather; fog, low cloud and pollution can also occur.
Centre: High air pressure • Wind flows from centre to periphery
Periphery: Low air pressure
Direction – Northern Hemisphere: Clockwise
Direction – Southern Hemisphere: Anti-clockwise

⚖️ Cyclone vs Anti-Cyclone

Feature	Cyclone	Anti-Cyclone
Pressure	Low Pressure (LP)	High Pressure (HP)
Wind direction (NH)	Anti-clockwise	Clockwise
Wind direction (SH)	Clockwise	Anti-clockwise
Weather	Stormy, rainy, destructive	Often dry/settled; may also have fog, low cloud or pollution
Wind flow	Periphery → Centre (inward)	Centre → Periphery (outward)
Centre	Mature tropical cyclone may have a relatively calm eye surrounded by an eyewall	High pressure core

⚡ Quick Recall

Cyclone and Anti-Cyclone have exactly opposite wind rotation in each hemisphere — if a cyclone spins anti-clockwise in the NH, the anti-cyclone spins clockwise there.

🇮🇳 Selected North Indian Ocean Cyclones — 2023–2024

Year	Cyclones in India
2024	Remal, Asna, Dana, Fengal
2023	Michaung, Tej, Biparjoy

⚡ Quick Recall

North Indian Ocean names are contributed by panel members: Biparjoy—Bangladesh, Remal—Oman, Midhili—Maldives.

🌊 Major Cyclones (2022–2024)

Name	Time	Affected Areas	Origin	Naming Country
Cyclone Asna	25 Aug-2 Sep 2024.	Gujarat and Rajasthan were strongly affected by the precursor system; the cyclone later lay off Kachchh and adjoining Pakistan coast.	Arabian Sea.	Pakistan.
Cyclone Remal	24-28 May 2024.	Bangladesh and West Bengal, with heavy weather extending into Northeast India.	Bay of Bengal.	Oman.
Cyclone Michaung	1-6 Dec 2023.	North Tamil Nadu-Chennai region and coastal Andhra Pradesh; landfall occurred on the Andhra Pradesh coast.	Bay of Bengal.	Myanmar.
Cyclone Biparjoy	6-19 Jun 2023.	Kutch-Gujarat and adjoining Pakistan coast.	Arabian Sea.	Bangladesh.
Cyclone Mocha	9-15 May 2023.	Myanmar's Rakhine coast and nearby Bangladesh, including the Cox's Bazar region.	Bay of Bengal.	Yemen.
Cyclone Tej	20-24 Oct 2023.	Yemen, especially the Al Mahrah coast, with effects near Oman.	Arabian Sea.	India.
Cyclone Midhili	15-18 Nov 2023.	Bangladesh, with effects extending into Tripura and parts of Northeast India.	Bay of Bengal.	Maldives.
Cyclone Hamoon	21-25 Oct 2023.	Bangladesh, with weather impacts in Mizoram and other parts of Northeast India.	Bay of Bengal.	Iran.
Cyclone Asani	7-12 May 2022.	Coastal Andhra Pradesh, with significant weather over Andhra Pradesh and Odisha.	Bay of Bengal.	Sri Lanka.
Cyclone Mandous	6-10 Dec 2022.	Tamil Nadu and Puducherry, with effects also over adjoining south Andhra Pradesh.	Bay of Bengal.	United Arab Emirates (UAE).
Cyclone Sitrang	22-25 Oct 2022.	Bangladesh, with rain and wind impacts in West Bengal and parts of Northeast India.	Bay of Bengal.	Thailand.

⚠ Exam Trap

All these are Cyclones from the North Indian Ocean basin — none are "Typhoons" (Western Pacific term) or "Hurricanes" (Atlantic term), even though the underlying storm system is the same.

🌪️ AIR MASS, CYCLONE AND ANTI-CYCLONE World Geography · Ch 18

Warm Front

Cold Front

Stationary Front

Occluded Front

Tropical Cyclone

Temperate / Extra-Tropical Cyclone