The Atmosphere

Chapter 11Earth Science

2013-2014

Atmospheric Composition

• Ancient Greeks believed that air was an element that could not be broken down.

• We now know that air is made of a combination of many gases.

• These gases form Earth’s atmosphere.

Atmospheric Composition

• 99% of the atmosphere is made of nitrogen and oxygen.

• 1% is everything else: argon, hydrogen, carbon dioxide, water vapor, and other gases

Key Atmospheric Gases

• The amount of water vapor at any given time or place changes constantly.

• The percentage changes with the seasons, the altitude of a particular mass of air, and with the surface features beneath the air.

Atmospheric Composition

• The percentages of nitrogen and oxygen are important for life.– 78% nitrogen– 21% oxygen– 1% everything else

Key Atmospheric Gases

• The level of carbon dioxide and water vapor regulate the amount of energy the atmosphere absorbs.

• Water is the only substance in the atmosphere that exists in three states: solid, liquid, and gas.– When water changes state, heat is absorbed or

released, which leads to weather and climate.

Key Atmospheric Gases

• Dust and salt– Dust is carried into the atmosphere by wind.– Salt is picked up from ocean spray.– Both play a role in cloud formation.

• Ice– Third solid found in the atmosphere in the form of

hail and snow.

Ozone

• A gas formed by the addition of a third oxygen atom to an oxygen molecule.

• Exists in small quantities mainly in a layer well above Earth’s surface.

• Absorbs UV radiation from the sun.

• It is thinning.

Structure of the Atmosphere

exosphere

thermosphere

mesosphere

stratosphere

troposphere

Lower Atmospheric Layers

• Troposphere– Layer closest to Earth’s surface.– Contains most of the mass of the atmosphere.– General decrease in temperature from bottom to

top.– Upper limit – tropopause – varies in height from

around 16 km at the tropics to 9 km or less at the poles.

Lower Atmospheric Layers

• Stratosphere– Made up primarily of concentrated ozone.– Ozone absorbs more UV radiation than air, so the

stratosphere is heated.– Temperature gradually increases to the top of the

layer.– Upper limit – stratopause – located about 50 km

above Earth’s surface.

Upper Atmospheric Layers

• Mesosphere– No concentrated ozone.– Temperature decreases.– Upper limit – mesopause.

Upper Atmospheric Layers

• Thermosphere– Contains a tiny portion of the atmosphere’s mass.– Temperature increases with height to more than

1000°C.– Molecules are so far apart that it would not feel

warm to a human.

Upper Atmospheric Layers

• Exosphere– Outermost layer of Earth’s atmosphere.– Light gases (low mass) are found here – helium

and hydrogen.– No clear boundary between the exosphere and

space.– Fewer and fewer molecules until you are in space.

Solar Fundamentals

• Radiation– The transfer of energy through space by visible

light, UV radiation, and other forms of electromagnetic waves.

– All substances with temperatures above absolute zero emit radiation.

– About 35% is reflected into space.– About 15% is absorbed by the atmosphere.– Only about 50% is absorbed by Earth’s surface.

Solar Fundamentals

• Radiation– Different areas absorb energy and heat up at

different rates.– Does not heat air directly.– Air is heated by conduction and convection.

Solar Fundamentals

• Conduction– The transfer of energy that occurs when molecules

collide.– Example: Put a pot of water on the stove. The

element heats the lower molecules which then heat the molecules above them.

– Substances MUST be in contact with one another.– Affects only a very thin layer near Earth’s surface.

Solar Fundamentals

• Convection– The transfer of energy by the flow of a heated

substance.– Hot air rises, cools, falls, heats, rises.– Over and over again.

Temperature vs. Heat

• Temperature– A measure of how rapidly or slowly molecules

move around.– More molecules or faster-moving molecules in a

given space generate a higher temperature.– Fewer molecules or slower-moving molecules in a

given space generate a lower temperature.

Temperature vs. Heat

• Heat– The transfer of energy that occurs because of a

difference in temperature between substances.– The direction of heat flow depends on

temperature.– Heat flows from hot to cold.

Temperature vs. Heat

• Measuring Temperature– Degrees Fahrenheit (°F)– Degrees Celsius (°C)– Kelvin (K)• SI unit• No negatives. 0 K is absolute zero.

TF 9

5TC 32.0

TC 5

9(TF 32.0)

T TC 273.15

Temperature vs. Heat

• Dew Point– The temperature to which air must be cooled at

constant pressure to reach saturation.• Saturation – the point at which the air holds as much

water vapor as it possibly can.

• Condensation– When matter changes state from a gas to a liquid.– Water falls as rain.

Vertical Temperature Changes

• Temperature is cooler at higher elevations (i.e. mountaintop).

• Lifted condensation level – the height at which condensation occurs.

• Adiabatic lapse rate – rate at which unsaturated air to which no heat is added or removed will cool.

Air Pressure and Density

• Air Pressure– You are used to the pressure that the air exerts on

you.– Fish are adapted to live under the pressure of the

water.– Pressure increases with depth in the ocean.– Pressure decreases with height on land.

Air Pressure and Density

• Density– Proportional to the number of particles of air

occupying a particular space.– Varies with temperature:

Temperature Pressure Density

Increases Increases Decreases

Decreases Decreases increases

Temperature Inversions

• An increase in temperature with height in an atmospheric layer.

• Keeps the warm air lower and allows the cooler air to rise.

• Can lead to pollution problems.

• Has a great effect on weather conditions.

Wind

• Air moves in response to unbalanced heating and cooling of Earth’s surface.

• Imbalances create areas of high and low pressure.

• Wind moves from areas of high pressure to areas of low pressure.

• Changes with height in the atmosphere.

Relative Humidity

• Humidity– The amount of water vapor in the air.

• Relative humidity– The ratio of water vapor in a volume of air relative to how

much water vapor that volume of air is capable of holding.– Varies with temperature– Warm air is capable of holding more moisture than cool

air.– Expressed as a percentage.

Cloud Formation

• Clouds form when warm, moist air rises, expands, and cools in a convection current.

• As the air reaches its dew point, the water vapor in the air condenses around condensation nuclei.– Condensation nuclei – small particles in the

atmosphere around which cloud droplets can form.

Cloud Formation

• Clouds can form when wind encounters a mountain and the air has no place to go but up.– Orographic lifting– Warm air cools, water vapor condenses, and a

cloud forms.

Cloud Formation

• Stability– The ability of an air mass to resist rising.– Determined by how rapidly any given mass of air

cools.– Temperature of surrounding air masses and the air

mass itself also determine cooling rate.

Cloud Formation

• Latent Heat– The energy that is stored in water vapor and is not

released into the air until condensation occurs.– When condensation occurs, latent heat is released

and warms the air.– Water vapor holds lots of energy.

Types of Clouds

• Classified by their altitude and shape.

• Developed by English naturalist Luke Howard in 1803

Types of Clouds

• Height– Cirro• Describes high clouds with bases starting above 6000 m

– Alto• Describes middle clouds with bases between 2000 m to

6000 m.

– Strato• Refers to low clouds below 2000 m.

Types of Clouds• Shape

– Cirrus• Latin meaning: “hair.”• Describes wispy, stringy clouds.

– Cumulus• Latin meaning: “pile or heap.”• Describes puffy, lumpy-looking clouds.

– Stratus• Latin meaning: “layer.”• Describes featureless sheets of clouds.

– Nimbus• Latin meaning: “cloud.”• Describes low, gray rain clouds.

Cloud Formation

• Low Clouds– Stratocumulus or layered cumulus – covers much

or all of the sky in a given area– Stratus – i.e. lifted fog

• Middle Clouds– Altocumulus – resemble white fish scales– Altostratus – dark, but thin veils of clouds

Cloud Formation

• High Clouds– Cirrus – wispy, indistinct appearance– Cirrostratus – continuous layer – transparent to very

dense

• Clouds of Vertical Development– Clouds can grow vertically if the air that makes up a

cumulus cloud is unstable enough.– Cloud is warmer than the air and thus rises.– Can reach 18,000 m with the top part frozen.

Precipitation

• Coalescence– The process in which cloud droplets collide and

join together to form a larger droplet.

• Precipitation– Includes all forms or water, both liquid and solid.– Rain, snow, sleet, and hail.

The Water Cycle

• The constant movement of water between the atmosphere and Earth’s surface.

• Receives its energy from the sun.– Causes liquid water to change into a gas

evaporation.– Evaporated water rises into the atmosphere.– Water vapor cools and condenses to form clouds.– Water droplets combine and falls to Earth as

precipitation.

The Water Cycle

Precipitation

Groundwater

Runoff

Evaporation Condensation