 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 – 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