1. Warm-up What is the source of energy that drives convection within the atmosphere and oceans? A. Earth’s rotation B. The sun C. Hurricanes D. Heat from the inner core

2. Weather is the condition of the Earth’s atmosphere at a particular time and place

3. Earth’sAtmosphere

4. What gases is Earth’s atmosphere made of? Surprisingly, more Nitrogen than Oxygen!

5. What is an atmosphere? An atmosphere is the layer of gases that surround the planet. Ours is as thin as Earth’s crust!

6. Layers of the Atmosphere The four main layers of the atmosphere are displayed on the picture to the right. They are classified according to changes in temperature. Tropo means “turning” or “changing”. This is where weather occurs. –Temperature decreases with altitude (-6.1 o C for every km)

7. Troposphere Stratosphere Mesosphere Thermosphere Ionosphere Exosphere The layers of our atmosphere! Please Remember: Exo = satellites Iono = electric Thermo = hot Meso = protecting Strato = airplanes Tropo = weather

9. AirPressure

10. Properties of Air Air consists of atoms and molecules Because air has mass, it also has other properties, including density and pressure. Density = Mass / Volume

11. What is air pressure? Air pressure is the result of a column of air pushing down on an area. Denser air exerts more pressure than less dense air. (Air pressure = air pushing)

12. There are two main factors that affect air pressure. #1 = Altitude: how high up in the atmosphere you are.

13. Oxygen is heavier than Nitrogen, so it sinks to the bottom of the atmosphere. That means that the lower you are, the more weight is pushing on your head!

14. This also means that the higher your altitude, the less oxygen there will be to breathe! (This is why people take oxygen tanks when climbing Mt. Everest)

15. #2 = Temperature: When it is cold, the oxygen will huddle together, putting even more molecules on your head! ColdHot High PressureLow Pressure

16. Measuring Air Pressure An instrument called a Barometer is used to measure the changes in air pressure. There are two kinds of Barometers: Mercury barometers and Aneroid barometers.

17. The diagram shows how a mercury barometer works. A mercury barometer consists of a glass tube open at the bottom end and partially filled with mercury. The space in the tube above the mercury in is a vacuum – it contains no air. Mercury Barometer

18. Now we have barometers that don’t need liquid. Aneroid barometers These are Aneroid barometers, and work based on metal compression.

19. Aneroid Barometer Changes in air pressure cause the walls of the airtight metal chamber to flex in and out. The needle on the dial indicates air pressure.

20. Units of Air Pressure There are several different units. The U.S. average is just under 30 inches of mercury (29.52) National Weather Service maps indicate air pressure in millibars One inch of mercury equals approximately 33.87 millibars, so 30 inches of mercury equals about 1,016 millibars.

21. Isobars The wavy lines on a weather map are often associated with High pressure (H) and Low pressure (L) centers. Each line, called an isobar, connects the places that have the same atmospheric pressure.