9.10.4 Effect of the Earth’s rotation The Earth’s rotation on its axis causes air to be deflected, rather than travel in a straight line. This makes winds circle around high- and low-pressure systems. The direction depends on the hemisphere. As air moves from high to low pressure, winds circle in opposite directions in each hemisphere. In high-pressure areas, winds move anticlockwise in the southern hemisphere and clockwise in the northern hemisphere. This deflection is called the Coriolis effect (see FIGURE6 ).
SkillBuilder discussion Communicating 1. What do the lines in the image represent? 2. Which way does the wind move around the high-pressure area (H)? 3. How does the wind move around the low-pressure area (L)?
FIGURE6 Wind occurs when air moves from high-pressure areas to low-pressure areas, and its direction is affected by the Earth’s rotation.
1004
1008
1000
1012
996
992
H
L
984
998
9.10.5
How is wind represented on a weather map?
Differences in air pressure affect wind strength. You can check wind strength using weather maps, observing objects or using instruments. Winds are named by their source (e.g., a northerly wind comes from the north). Isobars on a weather map are not evenly spaced. In FIGURE7 , winds are strongest in the southern areas where isobars are close together and gentler in the northern areas where they are further apart. Symbols in FIGURE8 also show wind speed and direction more accurately on weather maps.
SkillBuilder discussion Concluding and decision-making, Communicating 1. What do the labels ‘HIGH’ and ‘LOW’ represent on the weather map? 2. Where is the wind strongest on this map, and how can you tell? 3. What does the shaded
area on the map indicate?
312 Jacaranda Humanities Alive 7 Victorian Curriculum Third Edition
Made with FlippingBook interactive PDF creator