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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