Unit 2 - Atmosphere and Wind

• Composition of Earth's Atmosphere


  • 78% Nitrogen
  • 21% Oxygen
  • 0.93% Argon
  • CO₂
  • Remaining %-Trace gases including Gez and water vapor
• Layers of the Atmosphere based on temperature

  • Troposphere
  • Stratosphere
  • Mesosphere
  • Thermosphere
  • Exosphere
• Pressure decreases with altitude
• Troposphere


  1. From the Earth's Surface up to 10 km

  2. Nearly all weather occurs here

  3. Temperature decreases with height

  4. Supports all life

  5. Winds increase with height

  6. Moisture content decreases with height
• Stratosphere


  1. From 10-50 km

  2. Very Calm

  3. Temperature increases

  4. Ozone contained here-good ozone-protects from UV rays
• Mesosphere


  1. From 50-85 km

  2. Temperature decreases

  3. Top of mesosphere Coldest

  4. Meteors burn up here

  5. Part of the atmosphere
• Thermosphere


  1. From about 85-500 km

  2. X-rays and UV radiation absorbed here

  3. Temperatures increase (caused by solar activity)

  4. Warmer during the day than at night

  5. Auroras (Northern and Southern lights) created here
• Exosphere


  1. 500-10,000 km

  2. Considered interplanetary or Outer Space

  3. Some molecules of gas (H, He, CO2)
• Ionosphere


  1. Upper mesosphere, thermosphere, and exosphere

  2. Contains ionized solar radiation
• Water vapor is the source of all condensation and precipitation
• Essentially all water on Earth is conserved
• Changes of State in the water cycle require energy in the form of heat transfer
• Latent heat is the stored heat that needs to be added or removed for a phase change
• Humidity is the quantity of water vapor in the air compared to the maximum it can hold at a given temperature and pressure
• Relative Humidity (RH) is the actual water vapor content compared with the amount of water air can hold at that temperature and pressure
• Two ways to change RH: Add or remove water vapor, Change the temperature
• Condensation occurs when air is saturated and further cooling causes clouds or dew
• Dew Point is the temperature to which air would have to be cooled for saturation to occur
• Elevated terrain acts as mechanisms that influence air flow, such as mountains
• Warm, moist air cools when forced over a topographic barrier, leading to adiabatic cooling and cloud formation
• Localized Convective Lifting occurs on warm summer days due to localized heating of Earth's surface
• Cloud Formation


  1. Results from adiabatic temperature changes

  2. Adiabatic temperature changes - temperature change with no loss or gain of heat energy

  3. As air rises, pressure decreases - air expands and then cools

  4. As air falls, pressure increases - air contracts and heats up

  5. No heat is gained or lost to the environment, only the volume changes
• Cloud Formation


  1. As a parcel of air rises, the parcel expands & cools

  2. As the air continues to rise, the air continues to expand & cool, cools to the dew point

  3. At the dew point, the parcel is saturated and condensation will occur (clouds)

  4. The rate of cooling for an unsaturated air mass is called the dry adiabatic rate = 10°C decrease for every 1000m of lift (vice versa for falling air)

  5. Once the parcel is saturated, it will continue to lift and cool but at a different rate called the wet adiabatic rate = 5-9°C for every 1000m of lift, varies with moisture content
• Adiabatic cooling occurs during cloud formation
• Atmospheric Lifting Mechanisms


  1. Collision of air masses

  2. Air has to go somewhere - goes up

  3. Localized Convective Lifting occurs on warm summer days

  4. Localized heating of Earth's surface creates local pockets of warm air

  5. Warm air rises, cool air sinks
• Adiabatic temperature changes occur during cloud formation
• The Coriolis Effect exists because the Earth rotates
• Global Winds move to the East in the Northern Hemisphere due to the Coriolis Effect
• Global Winds consist of a mixture of land and sea particles (such as air)
• High pressure systems (anti-cyclones) have pressure decreasing towards the center, wind blowing outward and clockwise, air mass expanding and moving downward, causing nice conditions, dry calm, and stable conditions
• Low pressure systems (mid-latitude cyclones) have pressure decreasing towards the center, wind blowing inward and counterclockwise, air mass shrinking and increasing in height, causing cloud formation and precipitation, unstable conditions, stormy weather
• Pressure and Wind: Heating of the earth creates pressure differences, and air flows from areas of high pressure to areas of low pressure, creating wind. The greater the difference in pressure, the greater the wind speed. Wind is named based on the direction it is coming from
• Isobar Maps show differences in pressure using lines of equal pressure. Closely spaced lines indicate a steep pressure gradient and strong winds, while widely spaced lines indicate a weak pressure gradient and weak winds
• Global Winds
• The Coriolis Effect exists in the Northern Hemisphere
• Global Winds move to the East and consist of a mixture of land and sea, the of particles (such as air) to the
• The uneven heating of Earth's surface increases areas of + Creates 15 hughout presume L 6985 makeup of Earth
• The atmosphere balances these heading differences by acting as a giant heat transfer system using Convechan
• Wind gets its name from the direction it is blowing om
• Wind Patterns


  • Polar Easterlies
  • Prevailing Westerlies
  • Trade Winds