Winds and convection

1. Winds and convection Movement of air

2. Air flows from dense to less dense

3. Air flows from dense to less dense. • We feel moving air as wind. wind dense air less dense air

4. How do we get uneven air density? http://www.youtube.com/watch?v=8qvlp4Lhva4&feature=endscreen cold air warm air Air expands upon heating  warm air is less dense than cold air. heating

5. candle

7. Facts about air movements • Air moves from dense to less dense area. • Warm air is less dense than cold air. • Warm air rises (because of low density). wind dense less dense warm cold

8. Convection

9. Convection • Warm air rises and is replaced by cooler air from the sides. • After rising, the warm air cools, flows to the sides (high up) and eventually sinks back to the ground away from the heat source making a loop.  warm and cold air is constantly in motion

10. risen air cools, flows to the sides Cooled air sinks back to the ground Cooled air sinks back to the ground warm air rises air flows to replace air that is rising at heat source = wind air flows to replace air that is rising at heat source = wind heat

11. Day Sea Breeze Night Land Breeze

12. Sea breezes Day: • Landwarms more quickly than water. • Air over the land heats up and rises. • Cooler air from the sea flows in to replace risen air (= sea breeze). • Risen air cools and sinks over the water.

13. Land breezes Night: • Water cools more slowly than land. • Air over the water warmer than air over the land -> air over water rises. • Cool air from the land flows in to replace risen air. • Risen air cools high up and sinks over the land.

14. Air circulation due to uneven heating of the earth by the sun. Equator warm air rises • At Equator: Air flows in from the sides.  WIND • Therefore: • The rising air eventually and flows to the . cools side cooled air sinks • Away from the equator: .

15. Convection causes six atmospheric circulation cells • The air flow close to the earth surface is wind we experience

16. Because of earth rotation: Corioliseffect -- deflects moving air masses: • to the right on northern hemisphere; • to the left on southern hemisphere.

17. Prevailing winds at the earth surface: Close to the poles: Polar east winds In middle latitudes: Mid-latitude West winds Around the equator: easterly Trade winds

18. Atmospheric convection • Atmospheric convection creates 6 atmospheric circulation cells (three on each hemisphere). • The airflow close to the earth surface of each circulation cell represents the main wind in the respective region. (= prevailing wind) • In middle latitudes (e.g. Montreal) winds come predominantly from the west. • The Coriolis effect diverts moving air masses to the right on the northern hemisphere and to the left on the southern hemisphere.

19. Measuring winds: wind direction • Weather vane • Points in the direction the wind is coming from. • Back half must be larger than front half.

20. Where does the wind come from? • Coming from: south west • Going to: north east

21. Measuring winds: wind speed • Wind speed is measured with an anemometer. • The faster the wind the faster the anemometer turns.

22. Measuring winds: wind sock • On bridges to warn cars of heavy winds • Indicates wind force and direction

23. Measuring facts about winds • A weather vane indicates the direction of wind; it points in the direction of the wind’s origin. • A weather sock indicates direction and force of wind. • An anemometer measures the speed of wind in km/h.

24. Memory check page 343