Chapter 10

The Terrestrial Atmospheres

Gasses etc.

Terrestrial CO₂, N₂, O₂, Ar

Jovian H₂, He, CH₄, NH₃

Pressure, Temperature, Density vs. Height

Where does it end?

Scattering of light? No orbital decay?

What do atmospheres do?

Greenhouse affect keeps surface warmer

Interact with light

Pressure

Weather

Magnetosphere (possibly)

On what does the temperature depend?

Distance from the Sun 1/d²

Albedo (reflectivity)

        (Rotation)

The formula:

With atmosphere

The Greenhouse Effect Is it good or bad?

Energy balance

Results of greenhouse

Different wavelengths react differently?

Absorption: molecules, excitation, ionization, dissociation

Transmission

Scattering

Where is the energy absorbed?

Atmospheric temperature profile

Troposphere, stratosphere, thermosphere, exosphere

What if an atmosphere has no ozone (UV absorber)?

Ozone hole

Why is the sky blue?

What if molecules did not scatter light?

Comparison of temperature profiles

What of the Moon and Mercury?

Magnetospheres

The Earth’s magnetosphere

The solar wind

Charged particle belts (Van Allen Belts)

Aurora

Weather and Climate

Weather is chaotic (as if you didn’t know)

Climate is more predictable.

Seasons

Tilt

Distance (if it is large enough)

Martian Seasons polar caps, dust storms, layering

Earth’s winds circulation patterns

but

Coriolis effect

Due to rotation Earth

Clouds and precipitation

Earth movie

Long term climate changes – ice ages, etc.

Sun’s decrease in temperature

Changes in tilt ( and lesser in orbit)

Albedo changes; aerosols, ice, etc

Greenhouse, temperature, pressure

The History of Atmospheres

Or is it mostly accounting

Creation

Outgassing

Evaporation/sublimation

Bombardment (thin atmospheres only)

Loss

Thermal Escape

Temperature (High temperature means high velocity)

Escape velocity of the planet

Mass of the atom (lower mass elements have higher velocity)

Bombardment

Solar wind stripping

Condensation

Chemical reactions

Comparison of Atmospheres

Mercury and the Moon

Temporary heavier gasses

Polar ice

Mars

ice movie

Must once have had water (and seas?) so must have had a substantial atmosphere

Active vulcanism kept it supplied

Some bombardment loss but most stripped by solar wind

Some in caps and permafrost.

Why did it change?

Venus

Completely covered

Cloud decks

Sulfuric acid, water droplets

Rain never reaches ground

Why are Earth and Venus so different

Early water on Venus evaporated and led to runaway greenhouse

Atmospheric water dissociated and was lost.

Earth

Kept cool by dissolving the CO₂ in oceans and keeping water precipitated

Kept warm by greenhouse regulation – now with biology.

Earth vs. Venus

So don’t get too close to the Sun

Why did Earth retain most of its water in a hydrosphere?

The temperature was not too hot (Venus) nor to cold (Mars)

Why does Earth have so little carbon dioxide (CO₂) in its atmosphere?

Current CO₂ is .03%

Oceans extract CO₂

There is 170,000 more CO₂ in oceans and rocks than in atmosphere

The bound CO₂ on Earth is about the atmosphere’s CO₂ on Venus

Does CO₂ act as a thermostat?

How to avoid a ‘snowball earth’.

With liquid water and plate tectonics the negative feedback keeps the Earth just right even as the Sun increases its energy output.

Do oceans affect plate tectonics? Venus had a dry lithosphere.

Why does Earth have so much oxygen (O₂)? How did the percentage evolve?

Life O₂ is continually being chemically removed so it must be resupplied

Why does Earth have an ultraviolet-absorbing stratosphere?

O₂ in the stratosphere then becomes O₃ and absorbs UV

Ozone hole

 CFCs provide chlorine which depletes the ozone

CFC level have dropped but mixing to the stratosphere is a long time

Global warming

Past

Present

Latest

Future