Objectives

1. Identify three properties of the atmosphere and how they interact. Explain why atmospheric properties change with changes in altitude. Section 11.2 Objectives Properties of the Atmosphere Review Vocabulary density: the mass per unit volume of a material

2. Atmospheric properties such as temperature, air pressure, and humidity describe weather conditions. Section 11.2 Properties of the Atmosphere New Vocabulary temperature inversion humidity saturation relative humidity dew point latent heat

3. Particles have more kinetic energy when they are moving faster, so the higher the temperature of a material, the faster the particles are moving – temperature is a measurement of the speed of the particles. Heat is the transfer of energy that takes place due to difference in temperature. Section 11.2 Temperature Properties of the Atmosphere

4. Section 11.2 Temperature Properties of the Atmosphere Measuring temperature Temperature can be measured in degrees Fahrenheit, degrees Celsius, or in kelvin.

5. Section 11.2 Air Pressure Properties of the Atmosphere Air pressure is the pressure exerted on a surface by the weight of the atmosphere above the surface. ( P = Force/area) The units for pressure are N/m2. Air pressure is often measured in units of millibars (mb), where 1 mb equals 100 N/m2.

6. Section 11.2 Air Pressure Properties of the Atmosphere Density of air The density and pressure of the layers of the atmosphere decrease as altitude increases. The air gets thinner as you go up.

7. Section 11.2 Air Pressure Properties of the Atmosphere Pressure-temperature-density relationship In the atmosphere, the temperature, pressure, and density of air are related to each other.

8. Section 11.2 Air Pressure Properties of the Atmosphere Pressure-temperature-density relationship Temperature, pressure, and density are all related to one another. If temperature increases, but density is constant, the pressure increases. If the temperature increases and the pressure is constant, the density decreases.

9. Section 11.2 Air Pressure Properties of the Atmosphere Temperature inversion A temperature inversion is an increase in temperature with height in an atmospheric layer.

10. Section 11.2 Air Pressure Properties of the Atmosphere Temperature inversion On cold clear winter nights, the ground is cold and does not radiate heat to the lower layers of the atmosphere. So the lower layers of air become cooler than the air above them.

11. Section 11.2 Air Pressure Properties of the Atmosphere Temperature inversion A temperature inversion can lead to fog or low-level clouds. In some cities, a temperature inversion can worsen air-pollution problems.(smog)

12. Section 11.2 Air Pressure Properties of the Atmosphere Wind The movement of air is commonly known as wind. In the lower atmosphere, air generally moves from regions of higher density and pressure to regions of lower density and pressure.

13. Section 11.2 Air Pressure Properties of the Atmosphere Wind Near Earth’s surface, wind is constantly slowed by the friction that results from contact with surfaces including trees, buildings and hills. Higher up from Earth’s surface, air encounters less friction and wind speeds increase.

14. Section 11.2 Humidity Properties of the Atmosphere Humidity is the amount of water vapor in the atmosphere at a given location on Earth’s surface.

15. Section 11.2 Properties of the Atmosphere Saturation occurs when the amount of water vapor in a volume of air has reached the maximum amount possible for that temperature. (RH = 100%)

17. Section 11.2 Humidity Properties of the Atmosphere Relative humidity The amount of water vapor in a volume of air relative to the amount of water vapor needed for that volume of air to reach saturation is called relative humidity. RH = water vapor content /water vapor capacity X100%

18. Section 11.2 Humidity Properties of the Atmosphere Relative humidity The dew point is the temperature to which air must be cooled at constant pressure to reach saturation. (RH = 100%)

19. Section 11.2 Properties of the Atmosphere The extra thermal energy contained in water vapor compared to liquid water is called latent heat.

20. Change of state diagram.

21. Section 11.2 Humidity Properties of the Atmosphere Condensation level A process in which temperature changes without the addition or removal of thermal energy from a system is called an adiabatic process. Adiabatic heating occurs when air is compressed, and adiabatic cooling occurs when air expands.

22. Section 11.2 Humidity Properties of the Atmosphere Condensation level Condensation occurs at the lifted condensation level (LCL). Air above the LCL is saturated and thus cools more slowly than air below the LCL.

23. 11 Study Guide Key Concepts Section 11.2 Properties of the Atmosphere Atmospheric properties, such as temperature, air pressure, and humidity describe weather conditions. • At the same pressure, warmer air is less dense than cooler air. • Air moves from regions of high pressure to regions of low pressure.

24. 11 Study Guide Key Concepts Section 11.2 Properties of the Atmosphere • The dew point of air depends on the amount of water vapor the air contains. • Latent heat is released when water vapor condenses and when water freezes.

25. 11 11.2 Section Questions Atmosphere What is the relative humidity of a parcel of air that has reached its dew point? a. 25 percent b.50 percent c.75 percent d.100 percent

26. 11 11.2 Section Questions Atmosphere A sealed container holds only air. If the temperature of the air inside the container is increased, which other property of the air also increases? a.volume b.density c.pressure d.mass

27. 11 11.2 Section Questions Atmosphere During which changes of state does water release latent heat? a.condensing and freezing b.evaporating and melting c.evaporating and freezing d.condensing and melting