Water in the Atmosphere: Weather and Climate





Gasses of the Atmosphere

Air Pressure

Solar Energy and the Atmosphere

It's the water! a general review

Vaporization and Condensation: a Change of Phase

The Global Transfer of Thermal Energy

Energy Transfer in the Atmosphere : a separate summary

Vertical Air Movements

Orographic Lifting

Air Masses and Fronts

The Local Climate Situation

Severe Storms




What is an atmosphere?

Ask for student input

Describe in general terms

Click here for information on the gasses of the atmosphere


Gasses of the Atmosphere

What is the atmosphere?


Has mass, gravitational attraction, etc.

Source? Volcanic and/or cosmic

Current composition - see fig. 9-1, page 228; w/overhead

Gasses, solids, and liquids

Stratification of the atmosphere - See fig. 9-3, page 230; w/overhead

Primarily based on composition, density, and temperature differences

See fig. 9-5, page 232

Has evolved through time

Carbon dioxide out, nitrogen & oxygen in


Air Pressure

Start with water pressure

Rock cod - a final trip to the surface

The Bends ("Without Remorse" by Tom Clancy pg. 333)

Submarines ("The Abyss" or "Crimson Tide")

Ammonites - nature's original submarine

Air has mass, gravity, weight

"Air pressure" is the weight of the matter at the surface

Decreases upward as atmosphere thins

14.7 lbs/in2 at the surface

Called "1 bar"

DEMO: meter stick and paper


Solar Energy and the Atmosphere

All energy comes from the sun

But what type of energy is it?

Where are the ski resorts?

If heat comes directly from the sun, they should be in the valleys

Solar energy reflected or absorbed - see fig. 9-9, page 239

Reflected: lost to space

Albedo: increased by reflective materials (snow, ice, clouds)

Absorbed: added to earth's energy budget

Energy can be transmitted in 3 ways - see fig. 9-11, page 241

Radiation - direct electromagnetic waves from the source

The sun, heat register in a room, etc.

Conduction - direct contact with a heat source

Electric stove, hot sand

Convection - transfer of heat energy due to density differences

Causes currents from areas of high density to low density

Differential heating of surface by the sun (radiation)

Equator vs. polar regions: these are the extremes

Langley: basic unit of solar energy

Differential heating results in high vs. low pressure areas

High pressure

Cold air, molecules closer together, increased density

Low pressure

Warm air, molecules farther apart, decreased density

DEMO: metal can with small amount of water

Heat, drive out air, seal, cool, can will collapse

What happened?

Global wind patterns

Air currents always move from high to low pressure

In a perfect world...

All winds would blow from south to north, or the reverse

Due to convection - describe energy and flow patterns

Heating at equator

Air becomes less dense and rises

Sets up convection cells

But it's not a perfect world

Spinning on its axis

Causes the Coriolis Effect - Describe

Changes wind patterns

Refer to "Planet Earth: Atmosphere" Time/Life page 84/85 with overhead


It's the water! a general review

What is water ­ H2O

A "di-polar" molecule - explain

Universal solvent - HOH

Neutrality between acids and bases

Origin of water

Volcanic vs. cosmic sources

Water runs downhill due to gravity

Fills up the low elevations - ocean basins, lakes, stream channels, etc.

Hydro cycle

Recycles water between different temporary reservoirs

Oceans       1,300,000,000 km3      97.2%
Ice             29,300,000 km3       2.15%
Groundwater      8,400,000 km3       0.625%
Lakes              230,000 km3       0.017%
Atmosphere          13,000 km3       0.001%
Streams              1,250 km3       0.0001%

The ocean is clearly the largest of these temporary holding facilities

Holds a huge volume of water

We're going to concentrate on the 13,000 km3 held in the atmosphere

Moisture is the most variable constituent of the atmosphere

Varies from 0% to 4%

May not seem like much, but...

Leads to fundamental and profound differences in global climate and surface conditions

Click here for a general overview of Water in the Atmosphere and the Transfer of Thermal Energy


Vaporization and Condensation: a Change of Phase

Very important aspects of the hydrologic cycle

Cleans and purifies the water

Transfers energy from the equator to the mid latitudes

Water in the ocean is held as a liquid

Somehow we have to get the liquid to change to a vapor

So it can enter the atmosphere as part of the hydro cycle

Water in the atmosphere is held as vapor - a gas

Somehow we have to get the vapor to change to a liquid

So it can fall as rain or snow

Talking change of phase here

Review the 3 states of matter - ice to water to steam

Heat energy is the driving force in all phase changes

Hot stuff is more 'excited' than cold stuff

Molecules move faster, therefore must require more energy

Reasonable to assume that any phase change results in the transfer of energy

Add energy to make vapor

Give up energy to condense back into a liquid

In the case of water, the change of phase requires 80 cal/cm3

This energy transfer works in both directions

Water to vapor - steals energy from environment and stores it in the vapor

Vapor to water - releases the stored energy back into the environment

Remember our global wind patterns?

The movement of large masses of air also results in the movement of large amounts of energy locked up in the vapor

More on this later when we discuss orographic lifting

Anyway, what causes the water to change phase so easily?

Let's make some moonshine

Anyone know how a still works?

Describe the process

Another important consideration

Warm air can hold more vapor than cold air

"Steamy Windows" by Tina Turner

Any ideas why this is true?

Probably related to the heat energy stored in the vapor

Greater thermal gradient when the air mass is cooler

Forces the vapor to give up the energy - causing condensation

Putting it all together...

Dew point - temperature where vapor condenses into liquid

Results in the formation of clouds

You can often "see" the dew point on a cloudy day

Look for groups of flat-bottomed clouds


The Global Transfer of Thermal Energy

The evaporation of water requires the addition of 80 calories of thermal energy per cubic centimeter.

This heat energy is robbed from the local environment

Is stored in the vapor

The energy remains locked up in the vapor until conditions change

The vapor condenses into the liquid phase

Releases the energy back into the environment

This addition and loss of energy directly affects our lives


When our bodies sweat, the water evaporates from our skin

Obtains the heat energy necessary for the phase change from the skin

Cools our bodies

In comparison, dogs have no sweat glands, so they have no cooling mechanism.

That's why they pant so much

All cooling comes from evaporation of water from their tongues.

Imagine no pores - we'd all pant like dogs

Wind chill factor

There is no actual drop in temperature - it only feels colder

Perception vs. reality

Global energy transfer and temperature moderation

Far more solar energy is received on earth at the equator than at the poles

Excess heat energy is used at the equator to evaporate seawater

Which is then transferred north and south to mid-latitudes

Cools, condenses, rains, and gives up the heat to areas which need it

This tends to moderate surface temperatures on earth

If you don't think this is important, try living on Mercury

Temperatures can vary up to 600 deg. C. from sunlight to shadow

And day to night


Vertical Air Movements

Review of the interaction between energy and air pressure

The earth is not uniformly heated

Areas of higher and lower temperature

Air masses take on the characteristics of the land they are in contact with

Cold, dry land = cold, dry air (high pressure)

Warm, moist land = warm, moist air (low pressure)

Hot air rises

Cools as it goes up

Condenses when it cools to the dew point

Causes formation of clouds

May lead to precipitation

Clearly, the equator has the most solar energy

And, thanks to current plate locations, very little land (mostly ocean)

Lots of langleys and lots of water

Rising, vapor-rich air masses

Cools and condenses

What land is at the equator gets pretty wet!

Show film "Clouds and Precipitation"

FK2345 (15 min) (grades 7-12)

With Video Study Guide


Orographic Lifting

This will be on the test, so pay attention!

What causes air to rise?

Several processes are related to this

Orographic lifting - my personal favorite

Remember the energy stored in the vapor when it entered the atmosphere?

Let's do something with it

And at the same time answer the question:

"Why are arid lands common on the leeward side of mountain ranges?"

So common they even have a name: Rain shadow deserts

The basic process: (Draw profile on board)

Warm, moist air from the sea moves inland

Deflected upwards due to mountains, etc.

Air rises, expands, and cools

Cools at 5.5 deg. / 1000 feet (dry adiabatic rate)

Eventually reaches the dew point

Condensation begins

Releases energy at a rate of 80 cal/cm3 during condensation

This heat is liberated into the atmosphere

Offsets the cooling of the air as it rises

Wet adiabatic rate (3.5 deg. / 1000 feet)

Air mass continues to rise, cool, and precipitate to top of mountain

Descends other side

Warms back up AT THE DRY RATE

Results in warm, dry air on the lee slopes of mountains

This warm dry air is hungry for water - and is capable of holding quite a bit

Evaporates all it can find - adds to desert situation

Therefore, the simple loss of water vapor from the atmosphere results in an energy transfer to the atmosphere

Which results in heating of the air mass


Air Masses and Fronts

Another process which causes air to rise (and cool to the dew point)

Review the interaction between energy and air pressure

The earth is not uniformly heated

Areas of higher and lower temperature

Air masses take on the characteristics of the land they are in contact with

Cold, dry land = cold, dry air (high pressure)

Warm, moist land = warm, moist air (low pressure)

Results in large areas of atmosphere with differing pressure and energy

There are 6 major air masses which affect the U.S. (refer to overhead)

Contacts between air masses are called fronts

Most "climate" occurs at fronts

Cold front vs. Warm front (see overhead)

Both result from the meeting of a cold air mass and a warm air mass

Both result in the warm air rising over top of the cold air

Main difference:

Cold front: the cold air is moving and "invades" the warm air

Forcing it up and over the cold air

Warm front: the warm air is moving and slide up and over the cold air

Both form low pressure areas due to rising air

Which may lead to condensation and precipitation

Results in some great frontal battles in the mid-west!

More on this later when we discuss thunderstorms and tornados


The Local Climate Situation

Been here over 20 years

Always worked hard and hoped for great time off

Noticed 2 things early on

Summer work - hot as blazes for 2 weeks (also very dry)

Then cool down 'til the next heat wave

Maybe even a bit of rain

DIGRESS TO: redwood roof of Selma house

Winter's off - lots of time but also lots of fog

Lived in Grants Pass

Either raining, or cold & foggy

Cold/foggy come in 2 week stretches

This 2 week pattern seems to hold - watch for it

Both summer (hot & dry) & winter (cold & foggy)

Associated with high pressure systems in both cases

Talked to National Weather Service meteorologist about this

Confirmed the 2 week pattern for the high pressure systems

Cause is very uncertain - it just happens?

Look what has happened in our area over Christmas / New Year (1997)

Storm after storm leading to an approx. 50 year flood

Then the high settles into the area

Cold and foggy indeed!

Consider this: It really wasn't that cold (it was January, after all)

Lows were in mid-high 20's

It could have been much colder

With the heavy rain and saturated ground (saturated everything!)

What would happen if we'd had a 50 year freeze following the flood?

Relate O'Brien cabin wet/freeze story


Severe Storms

El Niño

El Niño Home Page (PEML/NOAA)

El Niño: University of Illinois

El Niño Index: USA Today

Information about El Niño: USA Today


Thunderstorm information index: USA Today

Supercells have unique characteristics


Tornado information index: USA Today

How tornadoes are classified: Fujita Scale

Index to information on tornadoes



Guide to hurricane science and technology: USA Today

Latest Hurricane information