Tropical cyclones

Definition, formation & dissipation

For geography gcse 2016/17

Crafted by Jadon Farguson

What's a tropical cyclone? Also called typhoons or hurricanes (depending on which part of the earth they're in), tropical cyclones are weather systems with winds of more than 118km/h and heavy rain. They form over oceans in warm areas.

TermsWe’ll be using these words a lot, so it's good to know what exactly they mean.

➔ Latitude The angular distance of a place north or south of the equator

➔ EyeThe center of a tropical cyclone, an area of clear conditions created by air converging at the center of the storm and sinking

➔ Eye wallA thick bank of cloud around the eye with high wind speeds and heavy rain

Plus here's 2 types of cloud you'll be talking about a lot...Cumulonimbus clouds are tall clouds that form in the upper

troposphere when moisture in cool air condenses, especially at the ITCZ. Cirrus clouds appear as thin, wisp-like formations at high altitude.

We're now going to look at how they form

BtwThree things must be in place for tropical cyclones to form

And here they are

➔ 1Temperature

➔ 2Winds

➔ 3

Coriolis force

Temperature

A large, still, warm ocean where the surface temperature exceeds 26.5 C over long periods is required.

This helps a body of warm air to develop. Tropical cyclones form in late summer when oceans have warmed (mid July to September in the northern hemisphere and mid January to March in the southern).

Winds

Strong winds in the troposphere, 10-12km above the earth's surface, are needed to draw warm air up rapidly from the ocean surface.

Coriolis force

A strong Coriolis force is required. Tropical cyclones do not form at the equator, where Coriolis force is minimal, but instead where the rotation is stronger, between 5 and 30 degrees latitude.

5 steps of how tropical cyclones work...

1Warm air currents rise from the ocean. As the warm air rises, more air rushes to replace it; then it too rises, drawn up by the draught above.

2Updraughts of air contain huge volumes of water vapour from 💦the ocean, which condense to produce cumulonimbus clouds.

Condensation releases thermal energy stored in water vapour, which adds power to the cyclone.

3

Coriolis force causes rising currents of air to spiral around the center, so it resembles a whirling cylinder. It rises and cools, and some of it descends to form the clear, cloudless, still eye of the storm.

4As the tropical cyclone tracks away from its source, it is fed new heat and moisture from the 🔥oceans, enlarging as it does so.

5

Once it reaches a landmass, it loses its energy from the ocean. Air pressure rises as temperature falls, winds drop, rainfall decreases and it decays into a mere storm.

Intensifying & dissipating

Why do cyclones…

Intensify?

The cyclone is powered by warm, moist air condensing to release thermal energy, generating up to 600trillion watts.

The warmer the ocean fueling the storm, the more intense the cyclone will be.

Dissipate?

1. When it reaches land, its energy source is lost

2. When it moves to water below 26.5 C

3. When it runs into winds blowing in different directions

Do you remember… ...How the eye forms?By some air spiralling round the center cooling.

...Where cyclones form?From 5 to 30 degrees latitude

...What's released by warm, moist air?Thermal energy

All three? ¡Eres un genio!