Temperature and Air Pressure

1. Temperature and Air Pressure RRB page 107-108

2. Changes in air temperature • Factors that control our weather: the daily weather cycle and the seasons • Temps are usually lowest right before sunrise and warmest in the mid-afternoon • Short-term factors that affect temps: Cloud cover and regional weather systems • Long-term factor that affects temps.: Seasons

3. Heating of the Atmosphere- Complete the Handout-page 108 • Conduction moves heat from Earth into the atmosphere as air touches Earth’s surface • Direct absorption of insolation from the sun by gases and aerosols moves heat into the atmosphere • Absorption of long-wave infrared radiation from Earth’s surface moves heat into the atmosphere • Much of the infrared absorption by the atmosphere is due to the presence of water vapor, methane and carbon dioxide • The larger the amounts of these greenhouse gases, the more heat is absorbed by the atmosphere

6. Condensation and sublimation release large amounts of stored heat, directly heating the atmosphere • Condensation and sublimation release this energy when clouds, fog, dew and frost form • The Coriolis Effect, which results from the rotation of Earth and wind, causes friction where the atmosphere and Earth’s surface meet

9. This friction produces heat, which is absorbed by the atmosphere • Heat energy is transferred within the atmosphere by convection, caused by differences in air pressure • Convection currents/Convection cells: energy within the atmosphere moves in a circular pattern, transferring heat • Winds are parts of the convection currents that are parallel to Earth’s surface

11. When a gas expands, its temperature decreases • When a gas is compressed, its temperature increases • When air rises in the atmosphere it expands and its temperature decreases • When air descends, it is compressed and its temperature increases • Usually, air temperature in the troposphere decreases with increasing altitude because as air rises there is less air above it and less air pressure, and thus the air expands and cools.

14. Cloud Cover • Cloud cover during the day reflect solar energy back into space generally making temps colder • Cloud cover at night acts like a blanket, holding heat energy to Earth, generally making temps warmer

15. Measuring Temperature • We measure temperature with a thermometer • Typically, a thermometer has a bulb of liquid that expands when heated and contracts (moves down the neck) when it is cooled • Temperature is measured in Fahrenheit, Celsius or Kelvin • ESRT PAGE 13 • Lines of equal temperature are called isotherms

16. What Causes Air Pressure? • Air pressure is caused by the weight of the atmosphere • DO NOT WRITE: Air is relatively light, but the atmosphere goes many miles above Earth, exerting a pressure of nearly 15 pounds per square inch • Write This: Air pressure is greatest at Earth’s surface and decreases with altitude • Air pressure is exerted in all directions, which is why we can’t feel it • Air pressure allows us to drink through straws- as you drink, you lower the air pressure in the straw. The air pressure on the surface of the liquid outside the straw is now higher than inside the straw.

17. Measuring Air Pressure • Barometer: instrument used to measure air pressure • All barometers measure the effect of the weight of the atmosphere • Meteorologists measure pressure in millibars (mb) • Pressure at sea level: 1013.2 mb • ESRT page 13

20. Exit Pass • In groups of 3-4.. WITHOUT LOOKING AT YOUR NOTES! • List two differences between rotation and revolution • What is condensation? • What is sublimation? • What happens to air temperature as a gas expands? • What happens to air temperature as a gas compresses or contracts? • Draw a picture of a convection cell