Convection in the Atmosphere

1. Convection in the Atmosphere Chapter 6 Notes

2. Composition of the Atmosphere • Atmosphere: a mixture of gasses that surround the Earth • Contains the oxygen you breathe and protects you from harmful rays from the sun. • Water Vapor: make up part of the atmosphere . When conditions change the water vapor can change to a liquid (rain) or solid (snow)

3. Atmospheric Pressure • The atmosphere is held around Earth by gravity. • Gravity pulls gas molecules toward Earth’s surface which causes Air Pressure.

4. Air Pressure • Air pressure is the measure of the force withwhich air molecules push on a surface. • Air Pressure is GREATEST at the surface of Earth because there is more of the atmosphere above you to push down on you.

7. Atmospheric Heating • Energy from the sun is absorbed by the atmosphere, land, and water and is changed into thermal energy.

8. Thermal Energy Transfer • Thermal energy transfer is heat moving from a warmer object to a cooler object. This is known as thermal energy transfer.

9. How is Heat Transferred? There are THREE ways heat can move. • Conduction • Convection • Radiation

10. CONVECTION • Convection is the movement that transfers heat within fluids and air (gas) • Heat is transferred by currents within the fluid or gas • Convection = VENTS (through air and liquid particles) • Convection moves in a circular pattern with warm rising and cold sinking.

11. Convection • Example, as air is heated, it becomes less dense and rises. Cool air is denser, so it sinks. As the cool air sinks, it pushes the warm air up. The cool air is eventually heated by the Earth's surface and begins to rise again. This is called a convection current

13. Atmospheric Temperature • Differences in the temperature of the atmosphere result from the amount of solar energy absorbed. • Some parts contain more gases which make them absorb more solar energy • Other parts contain less gases which mean they are absorb less solar energy and are cooler.

14. Impact of Temperature on Air Pressure • Warm air is less dense than cold air. Therefore, warm air has a lower air pressure and cold air has a higher air pressure. • The molecules in warm air are moving fast and are SPREAD farther apart. Therefore there are fewer air molecules in a given area to push down on you. The molecules in cold air move slower and are CLOSER together Warm Air Cold Air

15. Air Pressure is dependant onDENSITY • More dense air will have a higherair pressure- there are more air molecules in a given space to push down on you • Less dense air will have a lowerair pressure- there are fewer air molecules to push down on you. Less Dense= fewer particles to push down on you More Dense= more particles to push down on you

16. Impact of Elevation on Air Pressure • As you move up through the atmosphere, air pressure decreases. • There are fewer air molecules above you to push down on you, so the force of the air will be less.

17. Air Pressure Affects the Weather • Air pressure in a weather system reflects the amount of water in the air, which affects the weather. Lowair pressure usually results in Badweather: stormy, cloudy, overcast. Highair pressure usually results in Goodweather: clear skies, no precipitation

18. Air Rises at the Equator and Sinks at the Poles • Differences in air pressure are caused by unequal heating of the Earth by the sun.

19. Why do we have Wind? • Wind: the movement of air caused by differences in air pressure (When HIGH pressure air moves to replace LOW Pressure air) ( Convection Cells) • The greater the pressure differences, the faster the wind moves.

20. Pressure belts are found every 30º • Air travels in many large circular patterns called convection cells. • Convection cells are separated by pressure belts that include bands of high and low pressure every 30° of latitude

22. Coriolis Effect • The Coriolis effect is the apparent curving motion of winds and ocean currents due to Earth’s rotation. • Northern Hemisphere the winds traveling north curve to the east and winds traveling to the south curve to the west

24. Global Winds • The combination of convection cells found at every 30º of latitude and the Coriolis effect produces patterns of air circulation called global winds.

25. Polar Easterlies • The wind belts that extend from the poles to 60° latitude in both hemispheres are called the polar easterlies. • They are formed as the cold sinking air moves from the poles toward 60° north and 60° south latitude. • They responsible for bringing cold arctic air over the United States.

26. Prevailing Westerlies • The wind belts found between 30° and 60° latitude in both hemispheres are called the westerlies. • The westerlies flow towards the poles from west to east • The westerlies are responsible for bringing moist air to the United States.

27. Trade Winds • The winds that blow from 30° latitude almost to the equator are called trade winds. • The Coriolis effect causes the trade winds to curvewest in the Northern Hemisphere and east in the Southern Hemisphere • Early traders used these winds to sail from Europe to the Americas.

28. The Doldrums • The area where the trade winds meet. • There is very little wind because there is very low pressure. • This is why it is called the doldrums.

29. Horse Latitudes • At about 30° north and 30° south latitude, sinking air creates an area of high pressure. The winds are weak in this area called the horse latitudes. • Legend says that sailors would get stuck in this windless area. Instead of wasting drinking water they would through the horses overboard. • Most of the Earth’s deserts are located at this latitude.

30. Jet Streams: Atmospheric Conveyor Belts • Jet Streams are a narrow belt of strong winds that blow in the upper troposphere. • Can reach maximum speeds of 400km/h • Do not follow regular patterns • Important for pilots and meteorologists.

33. Local Winds • Local winds move short distances and can blow from any direction. • Shorelines or mountains can create local wind patterns

34. Sea Breeze- during the day, air over the ocean is cooler and forms an area of high pressure. The cool air flows to the land producing a sea breeze.

35. Land Breeze- at night air over the land is cooler and forms an area of high pressure. The cooler air moves toward the ocean producing a land breeze.

36. Sea and Land Breezes

38. Mountain Breeze- at night air along the mountain slopes cool . This cool air moves down the slopes into the valley producing a mountain breeze.

39. Valley Breeze – during the day, the sun warms the air along the mountain slopes. This warm air rises up the mountain creating a valley breeze.