ATMOSPHERE

ATMOSPHEREChapter 11

Section 11.1Atmospheric BasicsAtmospheric Composition

The Earth’s atmosphere extends from Earth’s surface to outer space. It is a blanket of gases that surround the Earth

The atmosphere is composed of gases:78% Nitrogen21% Oxygen1% Other Gases (Argon, Hydrogen, Carbon Dioxide, Water Vapor)

The amount of water vapor in the atmosphere is constantly changing based on the season, altitude, and features on the ground

Solids (dust and salt) combine with water vapor to create clouds

Ozone (O3) is a gas formed by the addition of a third oxygen atom to the diatomic oxygen that we breathe. It absorbs ultraviolet radiation from the Sun.

Structure of the AtmosphereTroposphereStratosphereMesosphereThermosphereExosphere

Troposphere… Lower Atmospheric LayerLayer closest to the Earth

Contains most of the mass of the atmosphere

Weather takes place here

Air pollution collects here

Temperatures decrease as you go up, the highest point is between 9-16km (Tropopause)

StratosphereLower Atmospheric Layer

Contains the ozone layer

Absorbs most of the ultraviolet radiation

Temperature increases from bottom up

Highest point is 50km (Stratopause)

MesosphereUpper Atmospheric LayerThere is no ozone in this layer

Temperature decreases as you rise within the level

The top of the layer is at 80km (Mesopause)

ThermosphereUpper Atmospheric LayerHas only a tiny portion of the mass

Extremely hot – more than 1000o C

You can’t feel the temperatures because the molecules are so far apart (so it wouldn’t feel warm to humans)

The Ionosphere is found within this layer, which contains electrically charged particles and layers of progressively lighter gases.

ExosphereUpper Atmospheric LayerOutermost layer of the atmosphere

Layer where Hydrogen and Helium are found

This layer will gradually turn into outer space There is no clear boundary between the

atmosphere and space, there are fewer and fewer molecules as you increase in altitude until eventually, there are none.

Solar FundamentalsThe Sun is the

source of all energy in the atmosphere

Energy transfers to Earth in one of three ways:1. Radiation2. Conduction3. Covection

RadiationThe transfer of energy through space by

visible light, ultraviolet radiation, and other forms of electromagnetic waves

All substances that have temperatures above absolute zero emit radiation

The Higher the temperature of a substance, the shorter the wavelength it emits

ConductionThe transfer of energy that occurs when molecules

collide

For conduction to occur, substances must be in contact with one another

Energy is transferred from particles of air near the Earth’s surface to the particles of air in the lowest layer of the atmosphere

Conduction affects only a thin atmospheric layer near the Earth’s surface

Convection The transfer of energy by the flow of a heated

substance

Pockets of air are heated, become less dense than surrounding air, and rise. As the war air rises, it expands and starts to cool. When it cools, it increases in density and sinks. The process then continues with constant rising and falling of air.

These convection currents are responsible for vertical motions of air, which causes weather.

Section 11.2State of the Atmosphere

When people discuss the weather, they’re describing the current state of the atmosphere.

Atmospheric properties are given to describe weather conditions, such as:

• Temperature• Air Pressure• Wind speed• Amount of moisture in the air

Temperature vs. HeatTemperature Heat

A measurement of how rapidly or slowly molecules move around

Faster molecules have a higher temperature

Slower molecules are cooler

Can be measured in degrees Fahrenheit, degrees Celsius, or Kelvin.

The transfer of energy that occurs because of a difference in temperature between substances

Heat flows from higher temperatures of an object to areas of lower temperature

Dew PointThe dew point is the temperature to which air must

be cooled at constant pressure to reach saturation

Saturation is when the air holds as much water vapor as possible.

Without saturation, condensation cannot occur.

Condensation occurs when matter changes state from a gas to a liquid.

Vertical Temperature ChangesIn general, as you go up in the troposphere,

the temperature goes down 10 degrees C for ever 1000m increase in altitude.

Lifted Condensation Level (LCL) is the height at which condensation occurs.

The height of LCL often corresponds to the base of clouds.

Air Pressure and DensityTemperature is proportional to pressure

Higher temperature higher pressureLower temperature lower pressure

Temperature is inversely proportional to density Higher temperature lower densityLower temperature higher density

There is an exception to this rule, known as temperature inversion, because the temperature increases with heigth in an atmospheric layer

The concepts of Wind and Relative Humidity

Wind Relative HumidityCool air is more dense than

warm air so it sinks, forcing warm air upward. The differences in density and pressure causes wind

Ultimately, wind is a rush of air that makes an attempt to relieve an imbalance between warm (less dense) air and cool (more dense) air

Wind is faster and stronger at higher altitudes where there are fewer structures to provide friction

The ratio of water vapor in a volume of air relative to how much water vapor that volume of air is capable of holding

Expressed as a percentage 100% is holding all of the water

vapor it can (saturated) 50% is holding half of the water

vapor it canVaries with temperatureThe warmer the air, the more

moisture it can hold because there is more space between the air molecules

Section 11.3Moisture in the Atmosphere

Cloud FormationWarm (less dense) air rises and cold (more dense) air

sinks. Clouds will 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 (small particles in the atmosphere around which cloud droplets can form), they combine with millions of others to form a cloud.

Clouds can also form when wind encounters a mountain and has no choice but to go up. This is referred to as orographic lifting.

When two different air masses meet, this too can create uplift and clouds will form (warm air is pushed up).

How quickly an air mass cools is based on its resistance to rising (stable air stays put). This is referred to as stability.

The energy that is transferred to the gas during the change of state is stored in the water vapor and will not be released until condensation occurs. This is referred to as latent heat.

Within a cloud, the process by which cloud droplets collide and join together to form a larger droplet is called coalescence. As this process continues, the droplets become too heavy and gravity eventually takes over… leading to precipitation.

Types of CloudsClouds are generally

classified according to a system developed in 1803.

Low clouds form below 2000m

Middle clouds form between 2000m and 6000m

High clouds form above 6000m

Types of CloudsClouds are named based on their shape:1. Cirrus – Wispy, stringy

clouds2. Cumulus – white, puffy

clouds3. Stratus – layered sheets

of clouds4. Nimbus – gray rain

clouds, low in the sky5. Fog – cloud that forms in

contact with Earth’s surface

PrecipitationWhen cloud droplets collide and join together to form a larger droplet it is referred to as coalescence

Once droplets become too heavy, they fall to the Earth as precipitation.

Precipitation is all forms of water that fall from the clouds.Four main types:1. Rain2. Snow3. Sleet4. Hail