Important gases in atmosphere as they relate to atmospheric pressure

State Change of water Humidity and dew points affecting weather Explain motion of hot and cold particles

› Heat stored in water vapor

Condensation of clouds Processes that lift air and cause cloud formation Cloud classification Precipitation processes Air pressure, barometer, annemometer Wind factors

Precipitation – any form of water that falls from a cloud› Rain, fog, snow, sleet, hail

Water vapor is the most important gas in the atmosphere› Only makes up a small fraction

3 states of water ? , ? , ? Solid, liquid, gas

Temperatures and pressure allow for the changes

Allows water to freely leave oceans as a gas & return as a liquid (water cycle)

All water passes through the atmosphere as water vapor.

Solid to Liquid› Energy is transferred in the form of heat› Latent heat – “hidden” heat

Ice melting

Liquid to Gas› Evaporation – motion of molecules enables

escape the surface of the liquid and become a gas (pool/tub – cooling)

Condensation – water vapor changes to a liquid state.

› Water molecules release their stored heat› Clouds and fog

Solid to a Gas› Sublimation – solid directly to a gas

No liquid state – dry ice› Deposition – vapor directly to a solid

Frost on car window

Humidity – general term for the amount of water vapor in the air

Saturation – number of vapor molecules leaving the surface equals the number returning› Saturated warm air contains more water

vapor than saturated cold aid› dew, fog & clouds require saturation

Relative Humidity – ratio of air’s actual water-vapor content compared with the amount of water vapor air can hold at that temperature.› How near saturation air is

› Can be changed in 2 ways Adding or removing water vapor Temperature

When water vapor content of air remains constant, lowering air temperature causes and increase in relative humidity, and rising air temperature causes a decrease in relative humidity

Dew Point – important measure of humidity› Temperature to which a parcel of air would

need to be cooled to reach saturation

High dew point temperatures indicate moist air

Low dew point temperatures indicate dry air

Hygrometer –› measures humidity

Heat can be quickly exchanged between the ground and the air above.› Night – surface radiates heat causing cooling

When air is compressed gas molecules increase movement and air temperature increases.

When air is allowed to expand, it cools.

Adiabatic Temperature Changes – temperature changes when no heat is added or subtracted. › adiabatic cooling

As molecules spread out with increase height and decreased pressure, they become less agitated and vibrate slower.

As a result, the temperature drops

› adiabatic warming- as air cools down, it begins to fall towards the Earth’s surface As it sinks, the pressure pushes air

molecules closer together, causing them to become more agitated and heating them up again.

As a result, their temperature rises, even though no heat has been added.

Processes that lift air – › 4 mechanisms –

frontal wedging convergence orographic lifting localized convection lifting

› Frontal Wedging – masses of warm air rise and collide with cold air. The colder air acts as a barrier and less dense air rises

Convergence – air in the lower atmosphere flowing together resulting in an uplift. (clouds and adiabatic cooling)

› Orographic lifting: elevated terrains act as a barrier to air flow

› Localized convection lifting – unequal heating may cause warmed pockets of air to be heated more than the surrounding air. Air moves upwards causing thermals

Clouds – form of condensation best described as visible mixtures of tiny droplets of water of tiny crystals of ice.› Show what is going on in the atmosphere› Classified based on form and height

Cirrus Cumulus Stratus

› Cirrus – high clouds, white and thin, whispy fibers, feathery

› Cumulus – rounded individual cloud masses “cauliflower “ structure

› Stratus – sheets or layers; no distinct individual cloud unit

3 levels of clouds› High – above 6000 meters› Middle – 2000-6000 meters› Low - below 2000 meters

High Clouds – thin and white often made up of ice crystals› Not precipitation makers› 3 clouds

Cirrus - Cirrostratus - flat Cirrocumulus - fluffy

Middle Clouds › Large and dense› White to grayish sheet covering› Infrequent light snow or drizzle› Altocumulus – rounded masses

Low Clouds › May produce light precipitation› Scalloped bottom› “rainy cloud”› 3 members

Stratus Stratocumulus nimbostratus

Vertical Development › Clouds not fitting in other categories› Bases in low height range and extent

upward› Cumulonimbus – rain and thunderstorms

Fog – clouds with base very near the ground› Radiation cooling or the movement of air

over a cold surface› Appearance and structure almost identical

to clouds

Fog Types› Caused by cooling

Earth’s surface cools rapidly by radiation

› Caused by Evaporation Cool air moves over warm water Rising water vapor meets cold air –

condenses and rises

To form – could droplets must grow in volume by roughly one million times

Types – depends on the temperature of the atmosphere

› Rain, snow, sleet, glaze, hail

2 precipitation processes:› Bergeron process› Collision-coalescence process

Bergeron Process› Supercooling and supersaturation

Readily freezes if impacts a solid surface Ice crystals grow until they are large enough to

fall

Collision-Coalescene process› Rain drops in warm clouds › Smaller droplets collide with smaller slower

droplets