The Atmosphere
Basic Structure
Composition
• Combination of many gases
– Nitrogen - 78%
– Oxygen – 21%
– Water Vapor – 0% to 4%
– Argon – 0.93%
– Carbon Dioxide – 0.03%
– Neon, Helium, Methane, Krypton, – 0.01%
Hydrogen, Oxone, Xenon
Key Atmospheric
Gases
• Amount of nitrogen and oxygen are critical
– Any significant change would end life on Earth
• Water vapor
– Helps with energy regulation
– Exists as solid, liquid and gas
• Carbon dioxide
– Helps with energy regulation
• Ozone
– Ultraviolet (UV) radiation shield
Atmospheric
Structure
• Lower Atmospheric Layers
– Troposphere
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Closest to Earth’s surface
Holds most of the atmosphere’s mass
Most weather occurs here
Gets colder as you get higher
From 9km (poles) to 16km (tropics) high
– Stratosphere
• Mostly made of ozone (O3)
• Gets warmer as you get higher
• Top of layer is about 50km above the Earth’s surface
Atmospheric
Structure
• Upper Atmospheric Layers
– Mesosphere
• Gets colder as you get higher
• Top of the layer is around 100km above Earth’s surface
– Thermosphere
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Holds a small part of the atmosphere’s mass
Gets warmer as you go higher (can exceed 1000oC)
Top layer is around 500km above Earth’s surface
Ionosphere – contains electrically charged particles
– Exosphere
• Outer most layer of Earth’s atmosphere
• Contains light gases Hydrogen (H) & Helium (He)
Solar Fundamentals
• The sun is the source of all energy in the
atmosphere
• Sun’s energy is transferred in 3 ways:
– Radiation – through visible light, ultraviolet (UV)
radiation & other forms of electromagnetic waves
– Conduction – passed from one molecule to the
next; must be touching
– Convection – flow of a heated substance
• Diagrams
– Structure of the Atmosphere
• pg. 273
– Solar Radiation
• pg.275
– Energy in Earth’s Atmosphere
• pg. 276
State of the
Atmosphere
Temperature and
Pressure
Temperature or Heat
• Temperature
– How fast or slow molecules move around
• More molecules = higher temperature
• Faster moving molecules = higher temperature
• Heat
– Transfer of energy between substances
– Flows from warmer to cooler
– Fuels atmospheric processes
Measuring
Temperature
• Fahrenheit (oF)
– Water boils at 212oF
– Absolute Zero at -523oF
Water freezes at 32oF
• Celsius (oC)
– Water boils at 100oC
– Absolute Zero at -273oC
Water freezes at 0oC
• Kelvin (K)
– Water boils at 373 K
– Absolute Zero at 0K
Water freezes at 273 K
Atmospheric
Temperature Changes
• Dew Point
– Temperature that air must cool to at constant
pressure to reach saturation
– Saturation is when air is holding as much water as
possible
• Air must be saturated for condensation to occur
• Lifted Condensation Level (LCL)
– Height at which air has cooled enough for
condensation to occur
– Point at which clouds form
Air Pressure and
Density
• Air is denser and has higher pressure closer to
the Earth’s surface
• Temperature – Pressure – Density Relationship
–T
–T
P
P
–T
–T
D
D
Temperature Inversion a pocket of warmer air in
between cooler air
Wind
• Cool air sinks because it is more dense
• Forces warm, less dense air upwards
• Wind moves from areas of high pressure to
areas of low pressure
– High and low pressure areas form due to uneven
heating of Earth’s surface
Relative Humidity
• Amount of water vapor in a volume of air
relative to how much water vapor the volume
of air can hold
• Warm air can hold more water vapor
• Expressed as a percent
Moisture in the
Atmosphere
Clouds
Cloud Formation
• Warm, less-dense air rises, expands and cools in
a convection current
– As the air reaches its dew point, water vapor
condenses around condensation nuclei (sea salt,
dust)
• Can also form from orographic lifting
– Wind encounters a mountain and is forced up
• Collision of air masses of different temperatures
Stability and Latent
Heat
• Stability – when an air mass resists rising
– Can become unstable if the air is cooler than the
surface beneath it
• Latent heat – energy stored in water vapor
– Released as water vapor condenses
– Warms the atmosphere
– This can give energy to a storm and make it more
intense
Types of Clouds
HEIGHT
SHAPE
Cirro –above 6000m
Cirrus – wispy, stringy
Cummulus – puffy,
lumpy looking
Stratus - featureless
sheets
Nimbus – low, grey
rain clouds
Alto – 2000-6000m
Strato – below 2000m
Fog – on the ground
Low Clouds
• Form from intense heating
– Summer sun shining on dark fields
• Air expands and rises, then begins to cool
• At LCL condensation occurs and a cloud forms
– If the cloud stay warmer than the surrounding air
it will continue to grow
– If not it will flatten and be spread out by wind
• stratocumulus, layered cumulus, stratus
Middle Clouds
• Altocumulus, altostratus
• Can be a mix of liquid water and ice crystals
• Usually layered
High Clouds
• Cirrus, cirrostratus
• Made of ice crystals
• Indistinct, continuous layer that sometimes
covers the sky
Vertical Development
Clouds
• A cumulus cloud that starts as a low cloud and
continues to grow through the middle heights
and beyond
• Becomes a huge cumulonimbus cloud with an
anvil shaped top
– Produce thunderstorms with torrential rains and
high winds
Precipitation
• Coalescence – when water droplets collide
and make a bigger droplet
– Primary force in warm clouds
• Four main types are rain, sleet, snow, hail