Cyclones and Anti-Cyclones

Cyclones and Anti-Cyclones – UPSC Geography Notes

Overview: Cyclones and anti-cyclones are large-scale air circulation systems that play a vital role in weather and climate. Understanding their formation, structure, and differences is important for UPSC Geography and disaster management topics.

Table of Contents

• 1. What is a Cyclone?
• 2. Mechanism of Cyclone Formation
• 3. Types of Cyclones
• 4. Structure of a Tropical Cyclone
• 5. Stages of Tropical Cyclone Development
• 6. Distribution of Tropical Cyclones
• 7. What is an Anti-Cyclone?
• 8. Differences Between Cyclone and Anti-Cyclone
• 9. UPSC Quick Revision Notes
• 10. Previous Year Question

1. What is a Cyclone?

Cyclone refers to an intense low-pressure system in which air moves inward in a spiral pattern. It is characterized by high-speed winds and heavy rainfall.

The term “cyclone” is derived from the Greek word kyklos, meaning “circle” or “coil.”

2. Mechanism of Cyclone Formation

Cyclones form due to uneven heating of the Earth’s surface, pressure variations, and the Coriolis effect.

• Step 1: Warm, moist air rises from the ocean surface, creating a low-pressure zone.
• Step 2: Surrounding air moves in to fill the low pressure and also rises.
• Step 3: Rising air cools and condenses, releasing latent heat which fuels the system.
• Step 4: Due to Earth’s rotation (Coriolis force), the wind spirals around the center — forming a cyclone.

3. Types of Cyclones

• 1. Tropical Cyclones:
  • Formed over warm tropical oceans (temperature > 26°C).
  • Associated with heavy rain, thunderstorms, and very strong winds.
  • Examples: Hurricanes (Atlantic), Typhoons (Pacific), Cyclones (Indian Ocean).
• 2. Temperate (Extra-Tropical) Cyclones:
  • Formed in mid-latitudes (30°–60°).
  • Associated with fronts where warm and cold air masses meet.
  • Common in North America and Europe.

4. Structure of a Tropical Cyclone

• Eye: Calm center with clear skies and low pressure.
• Eyewall: Surrounds the eye; has the most intense winds and rainfall.
• Rainbands: Spiral bands of clouds producing heavy rain and gusty winds.

5. Stages of Tropical Cyclone Development

1. 1. Formation (Tropical Disturbance): Weak low-pressure area forms over warm sea surface.
2. 2. Depression: System strengthens; winds reach 31–49 km/h.
3. 3. Deep Depression: Winds 50–61 km/h; circular pattern starts forming.
4. 4. Cyclonic Storm: Winds exceed 62 km/h; well-defined eye forms.
5. 5. Severe Cyclonic Storm: Winds 89–118 km/h; strong rotation and intense rainfall.
6. 6. Very Severe/ Super Cyclone: Winds > 118 km/h; massive destruction possible.

6. Distribution of Tropical Cyclones

• Most common between 5° and 20° latitude on both sides of the Equator.
• Do not form near the Equator (0°–5°) due to the absence of Coriolis force.
• Major Cyclone-Prone Areas:
  • North Atlantic → Hurricanes
  • Western Pacific → Typhoons
  • Indian Ocean → Cyclones (Bay of Bengal, Arabian Sea)

7. What is an Anti-Cyclone?

Anti-cyclone is a high-pressure system where air moves outward and downward in a spiral pattern. It is the opposite of a cyclone.

• Winds move clockwise in the Northern Hemisphere and anticlockwise in the Southern Hemisphere.
• Associated with clear skies, dry weather, and stable atmospheric conditions.

8. Differences Between Cyclone and Anti-Cyclone

Feature	Cyclone	Anti-Cyclone
Pressure	Low pressure at the center	High pressure at the center
Air Movement	Air moves inward and upward	Air moves outward and downward
Weather Condition	Cloudy, stormy, rainy	Clear, dry, and calm
Direction (Northern Hemisphere)	Counter-clockwise	Clockwise
Direction (Southern Hemisphere)	Clockwise	Counter-clockwise
Vertical Motion	Upward	Downward

9. UPSC Quick Revision Notes

Cyclone = low pressure + inward spiral + rising air.
Anti-cyclone = hi