What is Air?What is Air?

• It’s a GAS!

• Mostly Nitrogen= 78%

• Oxygen = 21%

• Argon = about 1%

• Trace amounts of other gases

Composition of Earth’s Atmosphere

VolumeVolume Define system

Molar Volume of any gas at STP = 22.4 L

Amount of GasAmount of Gas

1 Molar Volume (22.4 L) =

6.02 x 1023 particles (Avogadro’s number)

1 Mole

PressurePressure The force exerted by the weight of air molecules

Atmospheric pressure = 14.7 lbs/in2

Behavior of Behavior of GasesGases

Parameters Definition

Amount of gas Number of particles, mass

Volume Amount of space occupied

Temperature Average kinetic energy of the particles

Pressure Force exerted

Principles of Principles of MeteorologyMeteorology

• Foldable

• Envelope fold

• Add information at each of 4 stations

Station 1Station 1Temp vs. VolumeTemp vs. Volume

Charles’ Law (closed system, constant P)

As temperature decreases, volume decreases

As the air cools it condenses.

Station 2Station 2Temp Vs. DensityTemp Vs. Density

When temperature decreases, density increases

As cooler air condenses it becomes more dense and sinks forcing warmer air upwards.

Station 3Station 3Volume and PressureVolume and Pressure

Boyle’s Law (closed system, constant T)

As volume increases, pressure decreases

As warm air rises, it expands (volume inc). As volume increases, pressure it exerts decreases

Warm fronts = low pressure

Cold fronts = high pressure

Station 4 – Station 4 – Pressure and Pressure and TemperatureTemperature

Gay-Lussac’s Law

As pressure decreases, temperature decreases

As the pressure of the rising air decreases, the air cools. The moisture in the air condenses to form clouds.

When 3 factors When 3 factors change…change…

• Combined Gas law

• P1V1 = P2V2

T1 T2

• VOLUME increases (rising air)

• PRESSURE decreases (Boyle’s Law)

• TEMPERATURE decreases (Gay-Lussac’s Law)

FrontsFronts

Cold FrontCold Front

Cold air mass advances toward warm air mass

Cold air mass slides under warm air mass

Forces warm air to rise and cool rapidly

Can produce rapid temperature drops and severe weather

Forms cumulus clouds

Strong cold front forms cumulonimbus clouds, storms, tornado, snow squalls

Low humidity

Warm FrontWarm Front Warm air advances

toward cold air mass

Warm air slides over cold air

Front moves more slowly with a gentle rise in temperature

Produces less severe weather, steady precipitation lasting for days

Leading edge forms high cirrus clouds at first, then cirrostratus, altostratus, and nimbostratus later

High humidity

CondensationCondensation

Cool air causes water VAPOR to condense Cool air causes water VAPOR to condense - contains less moisture than warm air- contains less moisture than warm air

Relative humidity - a measurement of the amount of water Relative humidity - a measurement of the amount of water vapor in the atmosphere compared to the amount of vapor in the atmosphere compared to the amount of moisture that can be in gas form at a given temperature. moisture that can be in gas form at a given temperature.

Dew point - the temperature to which air would have to be Dew point - the temperature to which air would have to be cooled to become “saturated”. Once the air is cooled cooled to become “saturated”. Once the air is cooled enough, the water vapor condenses to form a liquid. enough, the water vapor condenses to form a liquid.

Rain and CloudsRain and Clouds

There is a fine There is a fine line line

• Precipitation and cloud formation is all about states of matter

When water evaporates at the surface, it is an invisible gas.

As the water vapor (gas) rises, it cools and condenses to a liquid droplet. Clouds are liquid! (condensed water vapor)

Rain is larger droplets of liquid that fall to the ground.

Careful explanationCareful explanation• Air does not “hold” water.

• So what can we say:

• Air is a mixture. Water vapor is commonly found in air. If the air is cold enough, water cannot remain in gas state and becomes liquid. The size of the drops and amount of water will determine if it can stay aloft or if the force of gravity is enough to pull the liquid to the ground.

AtmosphereAtmosphere Exosphere

Ionosphere

Thermosphere

Mesosphere

Stratosphere

Troposphere

AtmosphereAtmosphere

AtmosphereAtmosphereMisconceptions: The atmosphere traps radiation. The atmosphere “re-radiates” the radiation back to Earth.

The atmosphere works like a greenhouse, blanket or car.- NO!

True Statement- Radiation is absorbed by the atmosphere and radiates back to the Earth.

Two times more heat comes from our atmosphere than the Sun.

The atmosphere promotes convection instead of preventing convection.

Misconception?Misconception?

Weather StationWeather Station Temperature Barometric pressure Relative humidity Light Anemometer UVA/UVB