2.4F Tropical cyclones (HL) Notes

1. Tropical cyclones have a low-pressure centre (the eye) surrounded by spiralling bands of thunderstorms.
2. These systems are characterized by:
   1. Very strong winds (often exceeding 119 km/h)
   2. Heavy rainfall and flooding
   3. Thunderstorms and storm surges along coasts
3. Once sustained wind speeds reach 119 km/h or more, they are classified as:
   1. Hurricanes in the Atlantic Ocean and eastern Pacific
   2. Typhoons in the western Pacific Ocean
   3. Cyclones in the Indian Ocean and South Pacific

The Structure of a Tropical Cyclone

1. Eye: Central calm region of low pressure.
2. Eyewall: Zone of maximum wind and rain surrounding the eye.
3. Rainbands: Spiraling arms of heavy rain and thunderstorms extending outward.
4. Outflow: Air diverging aloft, which helps maintain low pressure below.

Conditions Required for Formation

1. Warm ocean surface: Sea-surface temperatures must exceed 26.5°C to supply sufficient latent heat.
2. Moist atmosphere: Abundant water vapour fuels condensation and releases energy.
3. Low wind shear: Calm upper winds allow vertical storm development.
4. Coriolis effect: Earth’s rotation causes the system to spin, giving it its spiral structure.
5. Pre-existing disturbance: A small low-pressure area acts as the seed for cyclone development.

Formation Process

1. Warm, moist air rises over the ocean surface.
2. Rising air cools and condenses, forming clouds and releasing latent heat energy.
3. The release of latent heat warms surrounding air, causing further uplift.
4. This process reduces surface pressure, drawing in more warm air.
5. Continuous evaporation and condensation maintain and intensify the storm.
6. The Coriolis effect causes the storm to rotate cyclonically (anticlockwise in the Northern Hemisphere, clockwise in the Southern Hemisphere).

Impacts of Tropical Cyclones

Environmental Impacts

1. Massive rainfall and flooding destroy vegetation and erode coastlines.
2. Saltwater intrusion damages freshwater ecosystems.