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

• 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• 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 Water freezes at 32oF– Absolute Zero at -523oF

• Celsius (oC)– Water boils at 100oC Water freezes at 0oC– Absolute Zero at -273oC

• Kelvin (K)– Water boils at 373 K Water freezes at 273 K– Absolute Zero at 0K

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 P – T P Temperature Inversion -

a pocket of warmer air in between cooler air

– T D – T D

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 CloudsHEIGHT SHAPE

Cirro –above 6000mCirrus – wispy, stringyCummulus – puffy,

Alto – 2000-6000m lumpy lookingStratus - featureless

Strato – below 2000m sheetsNimbus – low, grey

Fog – on the ground rain clouds

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