Edexcel GCSE Geography B (1GB0) — Hazardous Earth
When you unplug a bathtub, the water doesn't just drop straight down; it spins into a swirling vortex. Tropical cyclones act in a similar way but on a massive scale, drawing in surrounding air to create gigantic, spinning storm systems.
These storms are intense areas of low air pressure, meaning the atmospheric pressure is much lower than the surrounding environment. Central pressure is typically measured below (millibars (mb)).
They are enormous systems, measuring between and across, and reaching heights of to . To be officially classified as a tropical cyclone (hurricane or typhoon), sustained wind speeds must exceed .
Their intensity is categorised using the Saffir-Simpson Scale, which rates storms from 1 to 5 based solely on wind speed. For example, a Category 5 storm has catastrophic winds exceeding .
Tropical cyclones only form between and north and south of the equator. They never form directly at the equator () because the Coriolis effect is too weak there to initiate spinning.
The formation and rotation of the storm follow a clear physical sequence:
Step 1: Warm ocean air rises rapidly through convection, creating an area of extreme low pressure at the ocean surface.
Step 2: Air from surrounding higher-pressure areas rushes inwards to fill this void in a process called convergence.
Step 3: The rotation of the Earth creates the Coriolis effect, which deflects this incoming air and causes cyclonic rotation.
In the Northern Hemisphere, this deflection forces the storm to spin in an anti-clockwise direction. The entire system is continually powered by latent heat energy, which is released when rising water vapour undergoes condensation to form clouds.
Moving from the centre of the storm to its outer edges, the physical conditions change dramatically. You can visualise this structure as a series of distinct, concentric zones:
Students often state that the eye of the storm has 'high pressure'. While the pressure is relatively higher than in the eyewall due to sinking air, the entire tropical cyclone remains an intense low-pressure system.
In 4-mark 'Describe' questions about cyclone structure, examiners expect you to logically order your answer spatially, usually moving from the centre outwards (eye, eyewall, spiral rain bands).
Always specify that cyclones rotate anti-clockwise in the Northern Hemisphere, as Edexcel mark schemes specifically look for this directional precision.
If asked why a cyclone loses energy (dissipates) over land, you must mention BOTH the loss of the energy source (warm ocean water) AND the increased friction from the land surface.
Low air pressure
An area where atmospheric pressure is lower than the surrounding area, caused by warm air rising, cooling, and condensing.
Millibars (mb)
The standard unit of measurement for atmospheric pressure in tropical cyclones.
Saffir-Simpson Scale
A 1-5 rating system used to categorise a tropical cyclone based on its sustained wind speed.
Coriolis effect
The apparent deflection of moving air caused by the Earth's rotation, which forces cyclones to spin.
Convection
The process where warm, moist air rises rapidly above the ocean surface.
Convergence
The process where air from surrounding higher-pressure areas rushes inward to fill a low-pressure void.
Cyclonic rotation
The spiralling movement of a storm system, which spins anti-clockwise in the Northern Hemisphere.
Latent heat energy
The 'hidden' heat energy released during condensation that acts as the primary fuel for a tropical cyclone.
Condensation
The process where rising water vapour cools and turns into liquid water, forming clouds and releasing heat.
Eye
The calm, clear centre of a tropical cyclone, created by descending (sinking) air.
Eyewall
A tall cylinder of rising air surrounding the eye, containing the storm's strongest winds and heaviest rain.
Cumulonimbus clouds
Dense, vertically developed towering clouds that produce the intense rainfall in a tropical cyclone.
Cirrus clouds
Thin, wispy clouds found at the very top of the cyclone canopy where air flows outwards.
Put your knowledge into practice — try past paper questions for Geography B
Low air pressure
An area where atmospheric pressure is lower than the surrounding area, caused by warm air rising, cooling, and condensing.
Millibars (mb)
The standard unit of measurement for atmospheric pressure in tropical cyclones.
Saffir-Simpson Scale
A 1-5 rating system used to categorise a tropical cyclone based on its sustained wind speed.
Coriolis effect
The apparent deflection of moving air caused by the Earth's rotation, which forces cyclones to spin.
Convection
The process where warm, moist air rises rapidly above the ocean surface.
Convergence
The process where air from surrounding higher-pressure areas rushes inward to fill a low-pressure void.
Cyclonic rotation
The spiralling movement of a storm system, which spins anti-clockwise in the Northern Hemisphere.
Latent heat energy
The 'hidden' heat energy released during condensation that acts as the primary fuel for a tropical cyclone.
Condensation
The process where rising water vapour cools and turns into liquid water, forming clouds and releasing heat.
Eye
The calm, clear centre of a tropical cyclone, created by descending (sinking) air.
Eyewall
A tall cylinder of rising air surrounding the eye, containing the storm's strongest winds and heaviest rain.
Cumulonimbus clouds
Dense, vertically developed towering clouds that produce the intense rainfall in a tropical cyclone.
Cirrus clouds
Thin, wispy clouds found at the very top of the cyclone canopy where air flows outwards.
