What is air pressure and how does it affect us What is air pressure and how does it affect us? Do Now: What happens to temperature as you go up into the atmosphere? HW: Atmosphere worksheet

Atmospheric Composition Permanent atmospheric gases Earth’s atmosphere consists mainly of nitrogen (78 percent) and oxygen (21 percent). The amounts of nitrogen and oxygen in the atmosphere are fairly constant over time. Atmospheric Basics Copyright © McGraw-Hill Education

Atmospheric Layers Troposphere Stratosphere The layer closest to Earth’s surface, the troposphere, contains most of the mass of the atmosphere and is where weather occurs. In the troposphere, air temperature decreases as altitude increases. The tropopause is the altitude at which the temperature stops decreasing. Stratosphere Above the tropopause is the stratosphere, a layer in which the air temperature mainly increases with altitude and which contains the ozone layer. At the stratopause, air temperature stops increasing with altitude. Atmospheric Basics Copyright © McGraw-Hill Education

Atmospheric Layers Mesosphere Thermosphere Exosphere Above the stratopause is the mesosphere, in which air temperature decreases with altitude. Temperatures stop decreasing with altitude at the mesopause. Thermosphere The thermosphere is the layer above the mesopause and contains the ionosphere. Exosphere The exosphere is the outermost layer of Earth’s atmosphere and can be thought of as the transitional region between Earth’s atmosphere and outer space. Atmospheric Basics Copyright © McGraw-Hill Education

Energy Transfer in the Atmosphere Radiation Radiation is the transfer of thermal energy by electromagnetic waves. Thermal energy is transferred from the Sun to Earth by radiation. Conduction Conduction is the transfer of thermal energy between objects when their atoms or molecules collide Convection Convection is the transfer of thermal energy by the movement of heated material from one place to another. Atmospheric Basics Copyright © McGraw-Hill Education

Energy Transfer in the Atmosphere Radiation Incoming solar radiation is either reflected back into space or absorbed by Earth’s atmosphere or its surface. Atmospheric Basics Copyright © McGraw-Hill Education

Temperature Measuring 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. Measuring temperature Temperature can be measured in degrees Fahrenheit, degrees Celsius, or in kelvins. Properties of the Atmosphere Copyright © McGraw-Hill Education

Air Pressure Air pressure is the pressure exerted on a surface by the weight of the atmosphere above the surface. The units for pressure are N/m2. Air pressure is often measured in units of millibars (mb), where 1 mb equals 100 N/m2. Properties of the Atmosphere Copyright © McGraw-Hill Education

Air Pressure Density of air The density and pressure of the layers of the atmosphere decrease as altitude increases. Properties of the Atmosphere Copyright © McGraw-Hill Education

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. Properties of the Atmosphere Copyright © McGraw-Hill Education

Air Pressure Temperature inversion A temperature inversion is an increase in temperature with height in an atmospheric layer. Properties of the Atmosphere Copyright © McGraw-Hill Education

Air Pressure Temperature inversion If the land does not radiate thermal energy to the lower layers of the atmosphere, such as on a cold, clear, winter night when the air is calm, the lower layers of air become cooler than the air above them. A temperature inversion can lead to fog or low-level clouds. In some cities, a temperature inversion can worsen air-pollution problems. Properties of the Atmosphere Copyright © McGraw-Hill Education

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. 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. Properties of the Atmosphere Copyright © McGraw-Hill Education

Humidity Humidity is the amount of water vapor in the atmosphere at a given location on Earth’s surface. Relative humidity Saturation occurs when the amount of water vapor in a volume of air has reached the maximum amount possible for that temperature. 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. Properties of the Atmosphere Copyright © McGraw-Hill Education

Humidity Relative humidity The dew point is the temperature to which air must be cooled at constant pressure to reach saturation. The extra thermal energy contained in water vapor compared to liquid water is called latent heat. Properties of the Atmosphere Copyright © McGraw-Hill Education

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. Properties of the Atmosphere Copyright © McGraw-Hill Education

Humidity Condensation level At equilibrium, evaporation and condensation occur at equal rates, so the amount of water in the liquid form remains constant. Properties of the Atmosphere Copyright © McGraw-Hill Education

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. Properties of the Atmosphere Copyright © McGraw-Hill Education