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

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

Section 11.2 Properties of the Atmosphere Temperature 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.

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

Section 11.2 Properties of the Atmosphere Air Pressure 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.

Air Pressure Density of air Section 11.2 Properties of the Atmosphere Air Pressure 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.

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

Air Pressure Pressure-temperature-density relationship Section 11.2 Properties of the Atmosphere Air Pressure 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.

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

Air Pressure Temperature inversion Section 11.2 Properties of the Atmosphere Air Pressure 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.

Air Pressure Temperature inversion Section 11.2 Properties of the Atmosphere Air Pressure 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)

Air Pressure Wind The movement of air is commonly known as wind. Section 11.2 Properties of the Atmosphere Air Pressure 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.

Section 11.2 Properties of the Atmosphere Air Pressure 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.

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

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%)

Humidity Relative humidity Section 11.2 Properties of the Atmosphere Humidity 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%

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

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

Change of state diagram.

Humidity Condensation level Section 11.2 Properties of the Atmosphere Humidity 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.

Humidity Condensation level Section 11.2 Properties of the Atmosphere Humidity 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.

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.

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.

11 Atmosphere 11.2 Section Questions 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

11 Atmosphere 11.2 Section Questions 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

11 Atmosphere 11.2 Section Questions 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