Chapter 18

 Water vapor  Precipitation  Condensation  Latent heat  Heat is added but there is no temperature change because the heat is instead breaking bonds  Latent heat of evaporation  The energy required to change a liquid to a gas  Latent heat of condensation  Stored heat energy is released as a gas changes to liquid  Sublimination  Solid to vapor (dry ice)  Deposition  Vapor to solid (frost)

 Amount of water vapor in the air  Air is saturated when as much water is entering the air as is leaving it  Warm air can hold more water than cold  Relative humidity – how much water is in the air compared to how much it could hold (how close is it to being saturated)  If you change the temperature you change the relative humidity

 Dew Point  Temperature to which the air would need to be cooled to reach saturation (below that point you get condensation making dew)  High dew point temperature means moist air  Low dew point temperature means dry air  Hygrometer  Measures relative humidity

 Adiabatic Temperature Changes  When air expand it cools  When air is compressed it warms  Increasing in elevation means expansion and decreasing in elevation means compression  Water condenses as it cools (rises) making clouds  The wet adiabatic rate has a slower temperature change than the dry adiabatic rate because of condensation

 Orographic lifting  Air has to go over a physical barrier (mountain)  Results in a rain shadow on the leeward side  Frontal Wedging  Warm air and cold air collide (a front)  Warmer air rises over the colder air  Convergence  Air flowing in different directions meets and some goes up  Localized convective lifting  Unequal heating creates warm pockets and that air moves up

 Unstable air rises and stable air stays put  Environmental lapse rate – rate of change of air temperature with height  Stable air has a gradual decrease in temperature as altitude increases  Temperature inversion – temperature increases as altitude increases (colder closer to land)  Stable air forced up creates thin wide-spread clouds  Unstable air forced up result in storms and tornados

 Air has to be saturated  The water needs a surface  Grass or objects on the land  Condensation nuclei  Particulates in the air  Dust  Smoke  Salt  Makes clouds

 Cirrus clouds  High, white, thin  Cumulus  Rounded masses  Stratus clouds  Sheets of clouds covering the sky  High Clouds  meters  Cirrus, cirrostratus, and cirrocumulus  Include ice crystals  Middle Clouds  meters  Prefix of alto (Altocumulus)  Grey or white cover sometimes with drizzle or snow  Low Clouds  Stratus, stratocumulus, nimbostratus (make most of the rain)  Below 2000 meters  Nimbostratus usually forms when stable air is forced up

 Cloud – air cools and water vapor forms in higher elevation  Fog – air cools and water vapor forms near land  Warm air flows over a cooler ocean current then is blown over land  Earth cools rapidly on cloudless nights making a cooler layer near the surface  Cold air moves over warmer water

 Cold cloud precipitation  Bergeron process  Supercooling  Water suspended in air freezes at -40 o C so 0 o C to freezing is supercooled  Will freeze if it impacts a substance (freezing nuclei)  Supersaturation  Ice forms rapidly and makes water around them become ice = snowflakes  Warm Cloud precipitation  Collision-coalescence process  Water absorbing particle (salt) collects water vapors making large drops

 Rain  Snow  Usually will melt as they fall unless ground temperature is below 4 o C  Sleet  Falling ice  rain freezes near the surface  Glaze  Rain is supercooled and becomes ice when it impacts an object  Hail  Cumulonimbus clouds  Ice pellets collect supercooled water as it goes through the cloud