- What are they
- When and where
- Life cycle
- Structure
- The
Cyclone
Threat - Northern
Territory - Cyclone Tracy
- Warning System
Structure of Tropical
Cyclones
Eye
The centre or eye of a tropical cyclone is at the area of lowest pressure and is characterised by little or no wind and often a cloudless sky. In severe cyclones the eye usually shows up as a circular hole in the central cloud mass. The eye is usually about 40 km in diameter, but can vary between less than 10 km and more than 100 km.
Eye
Wall
Surrounding the eye is a wall of dense convective cloud rising about 15 km into the atmosphere. This is the eye wall and is where the most violent winds and heaviest rainfall occur.
Spiral
Bands
Radar and satellite observations of tropical cyclones reveal a distinctive pattern of convective cloud bands spiralling into the eye wall. These bands often extend up to 1000 km from the cyclone centre, and contain heavy rain and wind squalls.
Cirrus
Canopy
The extremely vigorous uplift of moist air within the convective clouds of the eye wall and inner spiral bands produces a massive outflow of cirrus cloud in the upper atmosphere. This forms a huge canopy over the cyclone, making satellite location of the system centre difficult during the early development stages, before the eye shows through the canopy.