Edexcel IGCSE Geography 复习笔记 3.1.2 Tropical Cyclones

• Low pressure areas (less than 950mb)
• Tropical Cyclones require specific conditions to form:
  • Sea surface temperatures over 27°C
  • Between 5° and 20° north and south of the equator
  • Low wind shear
  • Deep layer of humid air

Stages of Tropical Cyclone Formation

• In the right conditions a tropical cyclone can form rapidly. It follows a number of stages:
  • Warm, moist air rapidly rises forming an area of low pressure
  • Air from high pressure areas rushes in to take the place of the rising air
  • This air then rises forming a continuous flow of rising air
  • As the air rises it cools and condenses. This releases heat energy which helps to power the tropical cyclone
  • Air at the top of the storm goes outwards away from the centre of the storm
  • The Coriolis force causes the rising air to spiral around the centre.
  • Some of the air sinks in the middle of the storm forming the cloudless, calm eye.
  • The tropical cyclone moves westwards from its source
  • When a tropical cyclone makes landfall or moves over an area of cold water it no longer has a supply of warm, moist air and it loses speed and temperature. Rainfall and winds decrease

Features of Tropical Cyclone

• Tropical cyclones have a number of features:
  • Heavy rainfall
  • High wind speeds (over 74kmph)
  • Storm surges
  • Calm eye
  • Highest winds and heaviest rain in the wall of the eye
  • Diameter up to 800km