weather and climate lecture #2

The Planetesimal
Hypothesis

suggests that planets form through the accretion of particles in the same orbit through collisions

Slowly rotating and collapsing
cloud of dust and gas called a
nebula

The Sun condense from nebular
clouds with planets forming in
orbits around the central mass

Primordial Stage

Evolution of Earth’s Atmosphere;

~4.6 billion years ago
• Composition: Hydrogen and
Helium
• Strength: Gravity not strong
enough
• Structure: Not a differentiated
core (solid inner/liquid outer
core)
• Core important to deflecting solar
winds
• Magnetosphere: Earth’s
magnetic fields
• Earth’s atmosphere similar to
Jupiter
• Composed of hydrogen and helium

Evolutionary Stage

Evolutionary Stage
• Period: ~3.8 billion years ago
• Cause: “Degassing” into
atmosphere
• Earth cools
• Solid crust forms
• Dissolved gases from molten rock
are released into atmosphere
(volcanic eruptions) no free oxygen

Evolutionary Stage:

• Period: 3.6 billion years ago
• Heavy precipitation
• Earth continues to cool
• Water vapor condenses
• Clouds form
• Rains for thousands of
years
• Creation of oceans
• Most CO2 removed from
atmosphere to form
limestone (CaCO2)

Living Stage

Free first oxygen period”
• Period: ~3.3 billion years ago
• What happened: Photosynthesis
begins in oceans (H2O)
• Photosynthesis produces free
oxygen (O2) in the atmosphere
• Ozone layer forms from buoyant
water

H2 escapes to space, oxygen left
behind in the stratosphere
• Oxygen atoms bond to form ozone
(O3)

Current Composition of Atmosphere

classify the modern
state of the atmosphere into two
major categories:
• 1. Major/permanent/nonvariable
gases

• 2. Noble/variable gases

Major/permanent/nonvariable
gases

The concentration is virtually constant
near the earth's surface

Noble/variable gases

The concentration of a gas
that makes up the air varies
significantly from time to
time and place to place

What are the most important
variable/noble gases?

carbon dioxide: The carbon from CO2 is a fundamental building block for plants, which then form the basis of the entire biological food chain, it regulates Earth's temperature by trapping heat through the greenhouse effect, making the planet habitable, and is essential for photosynthesis

What are the most important
variable/noble gases?

Water vapor: As a potent greenhouse gas, water vapor absorbs outgoing infrared radiation from Earth, trapping heat also It is fundamental to the water cycle. When it changes state into liquid or ice, it releases latent heat, which drives atmospheric energy and powers storm systems.

What are the most important
variable/noble gases?

Ozone: Stratosphere: The ozone layer absorbs harmful ultraviolet (UV) radiation from the sun, protecting life on Earth.

The Montreal Protocol 1987

international treaty that protects the ozone layer by phasing out the production and consumption of ozone-depleting substances (ODS) like CFCs

Result: Concentrations of chlorine (from CFCs)
over Antarctica peaked in the early 1990s and
have declined since

The “atmosphere

A collection of
gases held near the Earth’s surface
by gravity
• Remains in balance between
gravitational force and buoyancy

Air

A simple mixture of gases that is
naturally, odorless, colorless,
tasteless, and formless blended
together so thoroughly that it
behaves as a single gas

Gravity

keeps molecules in the
atmosphere and oceans pinned to
the planet, giving them weight

different ways to
classify Earth’s atmosphere

Composition
• Temperature
• Function

Heterosphere
(layered)

Outer atmosphere
• 80 km (50 mi)
outward to
thermopause
• Gases layered by
weight/gravity
• <0.001% of
atmosphere mass

(layered cake)

Homosphere (mixed)

Inner atmosphere
• Surface to 80 km
• Gases evenly blended
• Except ozone layer
(O3) from 12 km to
50 km

(smoothie)

Troposphere

Altitude: 0 – 12 km
• Temp: Decreases with
height
• Heat Source: Ground
• 80% mass of the
atmosphere
• Our weather occurs
here
• “Weather Sphere”

Stratosphere

Altitude: 12 – 50 km
• Temp: Increases w/
height with absorption
of UV by ozone (O3)
• Heat source: Ozone
• Characters:
• Few clouds, dry
• Little vertical mixing

Mesosphere

Meso = “Midldle”
• Altitude: 50 – 80 km
• Temp: Decreases w/
height
• Coldest portion of the
atmosphere (-100° C)
• Noctilucent clouds
• Band of ice crystals that glow
in rare and unusual light

Thermosphere

Altitude: 80 – 600 km
• Temp: Increases w/
height
• High temperature
• Low density and heat
• Lots of energy
• Not a lot of molecules to
transfer kinetic energy
• Air is thin
• Thermopause
• Avg Upper Limit: 480 km
• Varies with sunspot activity
• “Heat Sphere”

Ionosphere

Upper mesosphere and
thermosphere between
roughly 80 and 600 km
(50 to 373 mi) in altitude
where nitrogen and
oxygen are ionized by
solar energy
• Absorption of cosmic
radiation – changes
atoms to a positively
charged ions
• Auroras

Aurora borealis (northern lights) and aurora
australis

Caused by gas molecules energized by charged
particles called the solar wind
• Found mostly near the poles where Earth’s
magnetic field concentrates solar wind’s particles

Ozonosphere

A portion of the stratosphere
that contains an increased
level of ozone is called the
ozonosphere
• Trace gas (0.000007% by
volume)
• Naturally occurring
• Absorbs radiation and warms
• Stratospheric Ozone: GOOD
• Absorbs UVB and UVC
radiation
• Tropospheric Ozone: BAD
• Unhealthy for humans