A Dynamic Planet: Atmospheric Structure, Dynamics and Global Climate (Lecture 2)

Name the 4 layers of the atmosphere in order from lowest to highest.

• Troposphere (0-10km)

• Stratosphere (10-50km)

• Mesosphere (50-85km)

• Thermosphere (85km <)

Name the fixed components of the atmosphere. State their proportions.

• 78% Nitrogen

• 21% Oxygen

• 1% Argon

Name the variable components of the atmosphere. State their proportions.

• 0-4% Water Vapour

• 0.01 ppm Ozone at the surface, 10 ppm at 25km altitude

What other particles are present in the atmosphere?

• Water droplets and ice - clouds and precipitation

• Dust and salt particles - aerosols

Why does the atmosphere have this temperature profile?

• Troposphere: relatively warm at the ground with temperature decreasing with height - due to heating from greenhouse effect

• Stratopause (boundary between the stratosphere and mesosphere) ~ 50km altitude

  is warm due to presence of ozone layer

  • Ozone reacts with UV which splits it apart – heat produced from the reaction

• Mesosphere: temperature decreases with height

• Thermosphere: temperature increases with height due to intense radiation from the Sun

  • O₂ and N₂ absorb UV and X-rays atomising them

  • They then absorb radiation ionising them giving out heat

Explain how the Earth maintains radiative equilibrium.

• When the incoming solar radiation is balanced by the outgoing thermal radiation.

• If more energy is absorbed than emitted, the Earth would heat up, and if more energy is emitted than absorbed, the Earth would cool down

Compare the Earth's atmosphere to those on other terrestrial planets in the Solar System

1. Mercury:

   • Very thin atmosphere composed mainly of trace amounts of hydrogen, helium, oxygen, sodium, potassium, and other elements.

2. Venus:

   • Thick atmosphere primarily composed of carbon dioxide (CO2), with trace amounts of nitrogen and other gases - creates a strong greenhouse effect

   • The atmospheric pressure at the surface of Venus is about 92 times that of Earth's, making it extremely dense.

3. Mars:

   • Thin atmosphere primarily composed of carbon dioxide (95.3%), with nitrogen, argon, and trace amounts of oxygen and water vapor.

   • The atmospheric pressure on Mars is only about 0.6% that of Earth's.

Define vapour pressure

The partial pressure of water vapor in the atmosphere (hPa).

Define Dewpoint temperarture

Temperature to which you would have to cool the air to reach saturation (i.e., the temperature at which dew would form).

What is adiabatic cooling?

• Adiabatic cooling occurs when the air parcel expands due to decreasing atmospheric pressure as it rises. The expansion leads to a decrease in temperature.

What is adiabatic warming?

• Adiabatic warming occurs when the air parcel compresses due to increasing atmospheric pressure as it descends. The compression leads to an increase in temperature.

What does the rate of adiabatic temperature change depend on?

• Whether the air parcel is saturated or unsaturated.

• Dry adiabatic lapse rate (10⁰C per km) applies to unsaturated air parcels

• Moist adiabatic lapse rate (5-8⁰C per km) applies to saturated air parcels

Why is moist adiabatic lapse rate lower then dry adiabatic lapse rate?

Condensation releases latent heat, mitigating the cooling effect

Define saturation of an air parcel

State where the air parcel holds the maximum amount of water vapour possible at a given temperature and pressure without condensing into liquid water or ice

Define latent heat of air parcel

Energy released when water vapour condenses when an air parcel reaches saturation (during cloud formation or precipitation)

Explain the Earth's general circulation.

• Earth has 3 cells in each hemisphere that are a part of the Earth’s atmospheric circulation: Hadley cell, Ferrel cell and Polar cell

• Hadley cell: converging air rises, produces clouds and then precipitates

• Ferrel cell: polar fronts at the surface are associated with a jet stream aloft. The jet streams blow from west to east.

  o   The jet stream separates polar air from tropical air.

  o   The jet stream is stronger in the winter hemisphere.

  o   The jet stream ridges over wide mountain ranges and troughs downstream of them.