Chapter 4 Moisture in the Atmosphere Chapter 4 Moisture in the Atmosphere Water on the Earth has three common states solid, liquid, and vapor Each with its own unique properties Earth is the only planet we know of that has all three forms Water on the Earth has three common states solid, liquid, and vapor Each with its own unique properties Earth is the only planet we know of that has all three forms

Phase ChangeHeat TransferType of Heat Liquid to Vapor cal absorbed Latent heat of evaporation (vaporization) Solid to liquid80 cal absorbedLatent heat of melting Solid to vapor680 cal absorbedLatent heat of sublimation Vapor to liquid cal released Latent heat of condensation Liquid to solid80 cal releasedLatent heat of fusion Vapor to solid680 cal releasedLatent heat of sublimation

Rain, ice, snow The water cycle

Distribution of water within the hydrological cycle

Atmospheric moisture ･ Water in the atmosphere ･ Requires -vapor pressure- the amount of pressure contributed by any volatile substance > e.g., water -air capable of "holding" vapor > dependent on temperature ･ Evaporation- -more water is becoming vapor than is condensing (becoming liquid) ･ Condensation -opposite effect

Relative humidity (RH) Water in atmosphere is dependent on temp. Saturation Vapor Pressure= -the maximum amount of water vapor that air can "hold" -temperature dependent -warm air "holds" more than cold air RH = Vapor Pressure Saturation Vapor Pressure measured by a number of devices

Saturation vapor pressure vs temperature

Condensation phenomena As RH goes to 100% water vapor condenses -i.e., it changes from vapor to liquid or solid forms clouds, rain, snow/ice, fog, dew must get air mass to reach saturation (approx) -accomplished by lifting & cooling, cooling, or increasing amount of water being vaporized usually have to have something for the water to condense onto...such as: -aerosols -dust particles and large molecules Condensation Factors Releases latent heat stored during vaporization

Environmental lapse rate 6.5° C per 1000 m = Avg. lapse rate dependent upon the local environmental conditions i.e., empirical = derived by measuring the avg temp of the air mass at the surface (T S ) and at the top of the troposphere (T T ) and the elevation difference between surface and troposphere (H ST ) (( T S - T T ) / (H ST )) Different from another more important lapse rate called Adiabatic lapse rate

Cloud formation (1:2) lifting of an air mass cooling due to adiabatic process -ADIABATIC - no energy lost or gained by exchanging with air that has different characteristics - explain this process...

Dry lapse rate (not at saturation) > -10° C per 1000 meters (-5.5 F / 1000 ft) -Wet lapse rate (at saturation point) >Heat (latent) gained as water condenses >air does not cool as fast > -6° C per 1000 meters (-3.3 F / 1000 ft) Adiabatic lapse rates (2:2)

Means of lifting Heating (aka convectional lifting) -warmed air rises (can also have a lot of water vapor) Orographic Lifting (mountains) -air encounters a barrier and goes over the top of it Frontal Lifting (air masses with different densities -cool air is more dense than warm air >slides underneath warm air, lifting it

Frontal lifting Warm Front Cold Front

Cloud terminology is descriptive Based on cloud form or shape Cirrus = feathered or wispy Stratus= layered Cumulus=puffy also linked to elevation low, middle, high, and vertically developed - - Alto = middle also linked to precipitation nimbo (-us) = rain sometimes linked to temperature warm vs. cold clouds Divided into 10 cloud Genera with corresponding species within each Genus

Cirrus Clouds - “ hair-like ” High Clouds "Feathers" or "Wisps" or small "Puffs" always High clouds- may be used a prefix Composed of Ice crystals - - a "mackerel" sky with small, puffed, cirrus clouds known as cirrocumulus - - and almost layered cirrostratus clouds

Perspective is everything from below, the low clouds look like stratus from above they look like cumulus in reality they are some combination of both! from below, the low clouds look like stratus from above they look like cumulus in reality they are some combination of both! - - three layers are visible here - - cirrus > > v. high - - altocirrus > > middle - - stratocumulus > > lower - - three layers are visible here - - cirrus > > v. high - - altocirrus > > middle - - stratocumulus > > lower

Stratus Clouds Layered clouds Can occur at all altitudes Can produce precipitation Stratus clouds produce dull gray looking skies These clouds are nimbostratus - layered and producing rain

Cumulus Puffy clouds with vertical development Clouds on the right -lifting due to a cold front Those on the left lifting due to heating and orographic effects

Cumulonimbus Clouds continued vertical development will eventually lead to Cumulonimbus clouds -these produce heavy local rains, strong winds, and thunderstorms Characterized by a tall, often flat-topped, puffy cloud form

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Orographic lifting creating a lenticular cloud Turbulance creating a lenticular cloud

Virga- rain that evaporates before reaching the ground Rainbow- rain acts as a prism, splitting white sunlight into its spectral colors

Mammatus clouds

Wall Cloud with lightning

Noctilucent Clouds “night glow” clouds Altocumulus Castelanus- aka “jellyfish” clouds

Precipitation Includes rain, drizzle, freezing rain, snow sleet hail, ice pellets, etc. Occurs when the weight of the condensed water becomes too great to keep it aloft Falls under the influence of Earth’s gravity Velocity doesn’t continue to increase as it falls Air resistance (friction) slows it down Achieves a stable speed called the terminal velocity Varies according to the size of the droplet/crystal Most precip forms by a process called the Bergeron Process

Dew/Frost Saturated air near the ground gets cooled to the saturation point Water collects (condenses) onto any surface available Frost means the temp is below freezing point (32°F Dew means temp is above freezing Dew point is the temp to which the air must be cooled in order to force condensation to occur happens under CONSTANT PRESSURE