Atmosphere

• Atmosphere: The gaseous envelope of air encircling the solid earth, held in place by the Earth’s gravitational attraction
• initial atmosphere composed mostly of hydrogen and helium
• outgassing of CO2 and H2O from the cooling center of the earth
• H2O condensed and rained, forming oceans
• CO2 dissolved from atmosphere into oceans
  • most is currently locked up in sedimentary rocks such as limestone
• O2 initially produced by photodissociation of H2o
• O2 forms ozone layer shields Earth from ultraviolet radiation
  • allowing life to form
• plants evolved producing O2 to form our current atmosphere

Atmospheric Components §

Near Earth’s surface

• nitrogen - makes up most of the atmosphere
• oxygen - second largest component, only 21% of atmosphere
• water vapor
  • Water vapor concentration is highly variable
• argon
• carbon dioxide
• ozone
• particles

Greenhouse Gases §

Other variable components near the surface. These are greenhouse gases. Greenhouse gases do not interact with solar radiation. Greenhouse gases interact with the long wave radiation the Earth emits, not the UV radiation from the sun.

• Water vapor (H2O)
  • Usually the most abundant and interacts the most
• Carbon Dioxide CO2
  • Allows more heat to be trapped, which then allows more water vapor to be trapped causing more problems. That’s why CO2 is a focus for reduction, because reducing it will reduce water vapor in the atmosphere
• Methane
• (theres more) The mixture of these dry gases is essentially uniform throughout the atmosphere up to about 80km (50 miles).
  Water vapor is the most important variable constituent. It plays a role in convective processes in two ways

1. Water vapor placed in the atmosphere (due to evaporation of water) adds to the buoyancy of air parcels, because most air is less dense than dry air
2. Water vapor that condenses to form convective clouds (especially thunderstorms). It releases 600 calories of heat energy per gram of water.

Air Parcels §

• Air parcels are a collection of all molecules contained within a volume enclosed by an imaginary stretchable impermeable film
• The volume is large enough to contain representative numbers of each constituent but small enough that properties do not change across the air parcel
• A dry air parcel consists of all the constituents of an air parcel except water
  • For example in dry climates like Nevada or Arizona, the air parcels probably don’t have water and are dry. But in like Florida, they are NOT

Atmosphere layers §

The properties of the vertical profile of atmospheric temperature convenietnly define four atmospheric shelsl with three intervening levels marking the transition between these four layers

1. Troposphere
   • This is the main one responsible for weather
   • Temperature here decreases as you go up
   • Averages about 10 kilometers in height, but no always the same height at every location
     • The height depends on the amount of solar radiation/heat that place gets, so the north pole has a shorter troposphere due to less heat, but the equator has a taller one due to more heat
   • Commercial aircraft tends to fly high up in the troposphere
   • Definition: The lowest layer next to the Earth’s surface, which contains all weather processes. Temperature decreases with height through this layer, which is often characterized by convective mixing (both in the horizontal and vertical directions)

• Tropopause (Transition)

2. Stratosphere
   • Temperature doesn’t change as you exit the troposphere, but then it starts to warm up as you go up
     • This is called an inversion layer
   • Radiosonde balloons go up into the stratosphere
   • Maximum ozone is where the stratosphere temperature starts to increase
     • The abundance of ozone in this layer keeps the stratosphere stable since it absorbs the UV radiation

• Stratopause (Transition)

3. Mesosphere
   • Sounding rockets are right about the mesosphere

• Mesopause (Transition)

4. Thermosphere
   • Out into space after here!
   • Low Earth orbit satellites are just above the thermosphere, just outside the atmosphere