Humidity

1. The relative measure of the amount of water vapor in the air • Psychrometer • Water vapor affects the density of the air. • Cold air is heavier than warm air. Humidity

2. Air Masses

3. A body of air that has the same temperature and humidity throughout. What is an air mass?

4. If a large body of air sits over an area of land or water for a long period of time, it will take on the characteristics of the land or water beneath it. • Temperature • Humidity How do air masses form?

5. Air masses over the equator will have high temperatures. • Air masses over polar regions will have low temperatures. • Air masses over water (maritime) will have high humidity (moisture content). • Air masses over land (continental) will have low humidity (moisture content). Location, Location, Location…

6. Air masses tend to form in areas with little wind. • Remember, they sit over an area for a long period of time without moving. Where do air masses form?

7. Air masses that form over water are called maritime. • Air masses that form over land are called continental. Labeling Air Masses

8. mT – maritime tropical • cT – continental tropical • mP – maritime polar • cP – continental polar • cA – continental arctic Classification of Air Masses

9. Location of Air Masses

10. mT – warm, moist air • cT – warm, dry air • mP – cold, moist air • cP – cold, dry air • cA – super cold, dry air Characteristics of Air Masses

11. Convection! How do air masses move?

12. Warm air rises, and cold air moves in to replace it. • A circulation pattern is formed. • Causes air and water currents to form Convection

13. Density! • Warm air rises. • Cool air sinks. How does convection work?

14. How do different air masses form? Reflection Question

15. Hurricanes

16. What is a hurricane? Hurricanes are tropical cyclones. They form in the southern Atlantic Ocean, Caribbean, Gulf of Mexico, and eastern Pacific Ocean. Their winds spiral outward in a counterclockwise, circulation pattern.

17. What conditions must exist for a hurricane to form? Low to medium winds blowing in the same direction 5–30 degrees north of the equator in the ocean Ocean surface temperature of greater than 80 F that extends down to about 150 feet deep (50 m) Lower atmosphere must be moist

18. How do hurricanes form? The air mass above the tropical waters takes on the temperature and humidity of the water beneath it. Incoming winds force the air upward. The warm, moist air rises, forming water vapor and clouds. Above the storm, the winds flow outward. Outside winds blow inward, and the cycle repeats.

19. How do hurricanes move? Hurricanes turn to the right, away from the equator, because of the Coriolis Effect caused by Earth’s rotation. You will learn about this phenomenon later in the lesson.

20. Where does the energy for a hurricane originate? The Sun heats the oceans. Warm air rises, and as it cools, it releases energy, fueling the hurricane.

21. Why don’t hurricanes form in higher latitudes? The temperature of the oceans is not warm enough. The distance is too far from the equator.

22. Hurricane Katrina

23. Reflective Question How do oceans play a role in the development of weather systems including hurricanes?

24. Winds

25. What is wind? The movement of air in a horizontal direction

26. What causes wind? The uneven heating of the Earth causes differences in air pressure.

27. Why does this happen? The Sun’s energy is more concentrated at the Equator and spread out more over the poles. Air over the equator is warm and less dense and has lower pressure. Air over the poles is cold and denser and has higher pressure.

28. Why does this happen? As warm air at the equator rises, cooler air from the poles will move in and replace it. Air pressure moves in a pattern from high to low.

29. Convection As warm air at the equator rises, cooler air from the poles will move in and replace it.

30. Global Convection Currents The density changes caused by temperature changes create convection cells. These cause circular patterns of air that circulate over the whole planet.

31. Global Wind Belts Where the convections cells meet, prevailing winds and jet streams form. They blow from one direction over a certain area of the Earth’s surface.

32. Jet Stream

33. Jet Stream • Forms high in the upper Troposphere between two air masses of different temperatures • Higher temperature difference = faster speed • Due to the Coriolis Effect, it flows around air masses. • Polar Jet: • It dips southward when frigid polar air masses move south. • It tends to stay north in the summer months.

34. Jet Stream Animation http://www.pbs.org/wgbh/nova/vanished/jetstr_five.html

35. Prevailing Winds • Named for the direction from which they blow: • Polar Easterlies – High latitudes blow east to west toward the equator • Westerlies – Mid latitudes blow west to east toward the poles • Easterlies (Trade Winds) – Low latitudes blow east to west toward the Equator

36. Prevailing Winds

37. Prevailing Winds Pressure belts form in between the wind belts.

38. MoreDirect Sun Hot 0 o Equator 90 o S 60 o N 90 o N 30 o S 60 o S 30 o N

39. Global Wind Belts The winds from the poles blow toward the equator. The winds from the equator blow toward the poles.

40. If wind is moving north and south, … …then why is it defined as the horizontal movement of air? Does the Earth stand still?

41. The Coriolis Effect As the Earth rotates counterclockwise, the winds bend and curve around the Earth. Gustave-Gaspard Coriolis, an engineer and mathematician, described this effect as an inertial force in 1835.

42. The Coriolis Effect In the Northern Hemisphere, winds bend to the right of their direction of travel. In the Southern Hemisphere, winds bend to the left of their direction of travel. Let’s try a little investigation to see how this works.

43. The Coriolis Effect Weather patterns and systems move in a circular motion due to the bending of the winds caused by the Earth’s rotation.

44. Equilibrium Our Earth is always seeking balance. In an effort to find balance, there is a continuous cycle of patterns. What is the driving force behind the changes that create these patterns?

45. Reflection Question How are winds produced?

46. Ocean Currents

47. Ocean Currents • Warm currents flow away from the equator. • Cold currents flow toward the equator.

48. Factors Influencing Currents Sun Wind Coriolis Gravity

49. Sun Energy from the Sun heats the water. Warm water is less dense that cold water. Warm water rises, and cold water sinks. As warm water rises, cold water moves it to replace it.

50. Convection Cycle