FIGURE3 shows the continuous cycle of evaporation, condensation and precipitation in cyclones. Initially, winds spin around an area 200–300 km wide. As the winds gather energy by drawing more warm, moist air, they speed up. In severe cyclones, winds can reach 295 km/h. The faster the winds, the smaller the spinning area (known as ‘the eye’), which can be about 30 km wide. Around the eye, winds and rain are at their strongest, but inside the eye, the air is calm, and the sky may be clear.
SkillBuilder discussion Concluding and decision-making 1. What direction is the wind spinning in the cyclone? 2. What happens in the centre of the cyclone, known as the eye? 3. How does warm air affect the cyclone’s formation?
FIGURE3 How a cyclone forms
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1 Warm sea water evaporates and rises. 2 Low pressure creates converging winds, replacing rising air. 3 Warm air spirals up quickly 4 Warm moist air is drawn in, providing more energy. 5 Water vapour fuels cumulus clouds. 6 Air moves away from the eye in the upper atmosphere. 7 The storm follows prevailing winds. 8 Descending air forms in the cyclone’s eye
9.12.2 What damage is caused by tropical cyclones? Tropical cyclones can cause major damage when they cross land. Gale force winds can tear roofs off buildings and uproot trees. Torrential rain and storm surges can lead to flooding. Low pressure also causes the sea level to rise, as shown in FIGURE4 .
TOPIC9 Water in the world 325
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