The Atmosphere

and is its importance to the Earth

• The atmosphere what is it?– A thin

envelope of gases that surrounds the Earth

• What does it do?– Controls the weather, hydrologic cycle,

and the climate of the Earth.

– Allows for life to exist on Earth

Atmospheric Composition

Ancient Atmosphere• Composition

– Carbon Dioxide

– Sulfur Dioxide

– Water vapor

– Nitrogen

• What is the source of the atmosphere?

• Could not support life – no oxygen

• Conditions changed 3.8 Ga (billion years before present)

• Water could condense (precipitation occurred)

• Life was generated (amino acids - aquatic microorganisms)

• CO2 dissolves in water and is used by MO – tied up in rocks

• Oxygen enters atmosphere

• Nitrogen remains – does not react with other chemicals

Layers of the Atmosphere

• Temperature stratifies the atmosphere

• Troposphere– Lowest layer – 0 to 15 km– Contains 80% of the mass of the

atmosphere.– Layer where weather occurs.– Temperature decreases with

height.

• Stratosphere – Occurs between 15 and 50 km

above the surface. – Temperature increases with

height.

– Contains ozone (O3) that shields the surface from ultraviolet (UV) radiation.

Energy Balance

Water Vapor • Water content in the

atmosphere is called the:

humidity

• Composition varies as a function of temperature.– Warm air holds > 40 g

H2O/Kg air

– Cold air holds < 5 g H2O/Kg air

• Addition/removal of water to the atmosphere requires/generates energy.

• Importance to climate – water vapor transfers heat from warmer to colder regions

• Latent heat – heat released or absorbed when matter changes state.

Latent Heat Cycle

Pressure

• Air Pressure – the weight of the overlying air– Measured in atm or bars (1 bar = 0.986 atm)

– 1 atm is the weight of the atmosphere at sea level ~ 1,035 g/cm2

• Mixture of gases in the atmosphere is not uniform– Air pressure decreases as one moves away from the

Earth’s surface

• As the pressure increases the density of the air increases

Air Density

Energy and the Atmosphere:Pressure, Water Vapor, & Weather• What drives energy within the Atmosphere?

Is the distribution of solar energy equal on the Earth’s surface?

• Solar energy is a function of both

• Location

• Time of year

Uneven Heating of Earth Surface

June 1998 Mean Surface Temperature

Daily Question

• Describe what would happen to a parcel of air that rises from the land surface up into the atmosphere. Your answer should discuss the density of the air, the temperature of the air, and the humidity of the air as it moves up. A sketch may be helpful in showing what is happening to the parcel of air at different altitudes.

What happens to hot air?• Warm air rises• As air rises it enters a

lower pressure area and expands

• Expansion cools the air – the cold air can hold less water

• Condensation occurs – clouds form (latent heat)

Which is more dense cold air or warm air?

Mechanism that lift air

• Density Lifting

• Frontal lifting

• Orographic lifting

• Convergence Lifting

Daily Assignment• Draw a circle to represent the Earth (label the

tropics (300 N and S), equator, and polar circles (600 N and S)

• Based upon what you know of air movement – indicate the direction of vertical movement at the labeled locations (keep in mind a balance of what goes up must come down)

• Indicate how the air moves from one region to another (horizontal lines either at the surface or higher in the atmosphere)

Global Air Circulation

Where Will Precipitation and

Evaporation Occur?

The Atmosphere in Motion

Air masses move from high pressure areas to low pressure areas

Coriolis Effect

Air Circulation Around a Pressure Low

Low and High Pressure Systems

• Low Pressure• Air moves up• Weather cloudy• Usually associated

with a cold front

• High Pressure• Air descending• Little to no clouds –

sunny

Wave-cyclones & Mid-Latitude Storms