Atmosphere

Chapter 11 Notes

Composition of the Atmosphere

• Currently:– Nitrogen (N2): 78%

– Oxygen (O2): 21%

– Argon (Ar)– Carbon dioxide (CO2)

– Water vapor (H2O)

• In the past :– Helium, hydrogen,

methane, ammonia

Variable Atmospheric Components• The following gases change over time:– Water vapor– Carbon dioxide: increase from 0.028% to 0.039%– Ozone

• Upper atmosphere: protection from ultraviolet radiation• Lower atmosphere: pollutant

– Particles:• Dust• Salt• Ice • Fungi• Bacteria

Atmospheric Layers

• Troposphere– Weather

• Stratosphere– Ozone layer

• Mesosphere• Thermosphere• Exosphere– Transition between

atmosphere and space

Thermal Energy Transfer (Heat)

• Radiation: transfer of heat by electromagnetic waves (example: heat lamp)– Visible and infrared EMR is absorbed and reflected by

clouds, atmosphere, and Earth’s surface– Rate of absorption varies from place to place, and

seasonally• Conduction: heat transferred through direct

contact• Convection: movement of heat through currents

in a liquid or gas

Radiation of Thermal Energy

Temperature and air pressure in the atmosphere

• Temperature = average kinetic energy of particles in a material, measured in ⁰C, ⁰F, or K

• Temperature increases if pressure is increased• Pressure increases if density is increased• Density decreases if temperature increases– Hot air rises

• Adiabatic heating and cooling: Air changing temperature without being heated or cooled—by changing pressure

Temperature Inversion

• Rapid cooling of land on a cold, clear night can cause a temperature inversion

• Temperature inversions can cause fog, haze, and smog

• Air pollution is trapped under the inversion layer

Wind

• Air moves from high pressure to low pressure: wind

• Pressure differences are caused by unequal heating and cooling of different regions

• Friction causes wind to slow down near Earth’s surface

• Wind speeds increase at higher altitudes

Humidity

• Amount of water vapor relative to the amount needed to reach saturation

• The dew point is the temperature to which air must be cooled to reach saturation

Cloud Formation

• Rising air cools, causing water vapor to condense

• Condensation nuclei (dust, ice, salt, or other solid particles) must be present for water droplets to stick to

• Rising air is unstable • Sinking air is stable (fair weather)

Clouds form from rising air

Types of Clouds

Types of Clouds

• High clouds (ice crystals): – Cirrus: wispy horse tails– Cirrostratus: fish scales

• Middle clouds: – Altocumulus: wavy rows or masses – Altostratus: thin layered sheets

• Low clouds:– Cumulus: puffy– Stratus: layers

Types of Precipitation

• Rain, snow, sleet, and hail are four main types of precipitation.

• Droplets in clouds grow through the process of coalescence when droplet collide and stick together, forming rain drops

• Hail forms when droplets move up and down through freezing and non-freezing air