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Winds

What causes wind? Chicago, Illinois, is known as the ‘windy city’. Why are some cities more windy than others?. Winds. The air around us is in constant motion (light breeze to strong winds). Wind is n ot evenly distributed over the Earth’s surface

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Winds

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  1. What causes wind?Chicago, Illinois, is known as the ‘windy city’. Why are some cities more windy than others?

  2. Winds • The air around us is in constant motion (light breeze to strong winds). • Wind is not evenly distributed over the Earth’s surface • The distribution of wind on Earth is determined by 2 geological phenomena: 1. Convection Cells 2. Coriolis Effect

  3. Convection Cells Unequal warming of the atmosphere (p. 334) How they work: • The sun rays hit the Earth and reach the ground. 2. The energy from these rays is absorbed by the ground.

  4. 3. Heat is emitted from the ground. 4. The heat warms up the surrounding air. 5. This air becomes lighter and takes up more space (volume).

  5. 6. This hot air rises, which creates a low-pressure area. 7. The cooler (and heavier) air above moves down in this low-pressure area. 8. The cycle starts over (hot air mass rises and cold air mass descends

  6. Coriolis Effect Rotation of the Earth (p. 335) • Gaspard Coriolis, a French mathematician and physicist discovered that air motion changes direction due to the Earth’s rotation. Coriolis Effect produces: • Trade Winds (Northeast and Southeast) : blow from east to west between the equator and the tropics • Prevailing West Winds: blow from west to east in the middle latitudes • Polar East Winds: diverted to the west in the polar regions

  7. Coriolis Effect cont.

  8. Characteristics of Wind Generally characterized by two elements: 1. Direction 2. Speed The direction of the wind is determined by a weather vane. • Point in the direction the wind is coming from (it’s origin). • For it to work... It’s back half must be larger than the front half. • Has a compass rose (indicates the cardinal points).

  9. Characteristics of Wind cont. The wind speed is measured with an anemometer. • Units: kilometres/hour A wind sock indicates both the force and direction.

  10. Sea Breeze There is almost always a gentle breeze blowing at the seaside.... Why? The breeze is created by the temperature difference between the air above the water and the air above the land.

  11. Sea Breeze cont. • Air above sand is warmer than air over sea. • This hot air rises and is replaced with the cool air from the sea. • This air warms up and the cycle continues. THE WIND BLOWS FROM THE SEA TO THE LAND

  12. Land Breeze At night, the opposite cycle occurs... The ground cools faster than the water (no sun). Therefore, the air above the sand is cooler than the air above the water. THE WIND BLOWS FROM THE LAND TO THE SEA

  13. Sea and Land Breezes

  14. Smog and Temperature Inversion The word SMOG is an amalgamation (combination) of the words SMOKE and FOG! This happens when a cool mass settles under a warm air mass (known as temperature inversion) • The cool air (heavier) stays close to the ground. • The warm air above prevents it from rising and dispersing. • All the air becomes stable (does not move →no more air flow). • The air becomes stagnant, which can be dangerous (pollutants).

  15. See p. 338 for a different diagram

  16. Smog and Temperature Inversion cont. • Smog is therefore a cloud of polluted fog. • It contaminates the air we breath because it keeps the atmospheric pollutants close to the ground (instead of circulating them). • Very dangerous if it stays for a long time.

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