Cyclones form when cold air meets warm, moist air over a tropical ocean with a surface temperature above 27 ° C. Cold air replaces the rising warm air, creating an intense low-pressure system. Winds can reach over 119 km/h. Cyclones are classified using the scale shown in TABLE1 .
TABLE1 Cyclone classification using the Saffir–Simpson Scale Category Wind gust speed, ocean swell
Damage
1 2 3
Less than 125 km/h, 1.2–1.6 m
Mild damage
126–169 km/h, 1.7–2.5 m 170–224 km/h, 2.6–3.7 m
Significant damage to trees
Structural damage, power failures likely
4 5
225–279 km/h, 3.8–5.4 m
Most roofing lost
More than 280 km/h, over 5.4 m
Almost total destruction
FIGURE2 World distribution of tropical cyclones by names used in different regions
ATLANTIC
OCEAN
JULY–OCT.
PACIFIC
Tropic of Cancer
OCEAN
SEPT.–NOV.
OCT.– NOV.
APRIL– JUNE
Equator
DEC.–MARCH
INDIAN OCEAN
ATLANTIC
OCEAN
DEC.–MARCH
Tropic of Capricorn
Key
Typhoons (term used in Asia)
Hurricanes (term used in United States)
5000 km
0
2500
Tropical cyclones (term used in Australia)
Tornados/severe storms
Source: Spatial Vision
SkillBuilder discussion Concluding and decision-making 1. Study FIGURE2 . Which areas are affected by typhoons, according to the map?
2. In which months do cyclones occur in Australia? 3. What term is used for storms in the United States?
324 Jacaranda Humanities Alive 7 Victorian Curriculum Third Edition
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