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Chapter 4Moisture in the AtmosphereChapter 4Moisture 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 Change Heat Transfer Type of Heat
Liquid to Vapor 540-590 cal absorbed
Latent heat of vaporization
Solid to liquid 80 cal absorbed Latent heat of fusion
Solid to vapor 680 cal absorbed Latent heat of sublimation
Vapor to liquid 540-590 cal released Latent heat of condensation
Liquid to solid 80 cal released Latent heat of fusion
Vapor to solid 680 cal released Latent heat of sublimation
Rain, ice, snow
The water cycleThe water cycle
Distribution of water within the hydrological cycle
Atmospheric moisture• Water in the atmosphere
• Requires
- vapor pressure- the amount of pressurecontributed by any volatile substance > e.g., water
- air capable of "holding" vapor> dependent on temperature
• Evaporation-
- more water is becoming vapor than iscondensing (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 aircan "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, orincreasing amount of water being vaporized
• usually have to have something for the waterto condense onto...such as:
- aerosols -dust particles and large molecules
Condensation FactorsReleases latent heat stored during vaporization
Environmental lapse rate6.5° 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 (TS) and at the top of the troposphere (TT) and the elevation difference between surface and troposphere (HST)
(( TS - TT ) / (HST))
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 byexchanging with air that has different
characteristics-
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 ratesAdiabatic lapse rates
Means of lifting• Heating (aka convectional lifting)
- warmed air rises (can also havea lot of water vapor)
• Orographic Lifting (mountains)
- air encouters a barrier andgoes over the top of it
• Frontal Lifting (air masses withdifferent densities
- cool air is more dense thanwarm air> slides underneath warm air,lifting it
Frontal lifting
• Warm Front
• Cold Front
Cloud terminology is descriptiveCloud terminology is descriptiveBased on cloud form or shapeBased on cloud form or shape
• • Cirrus = feathered or wispyCirrus = feathered or wispy
• • Stratus= layeredStratus= layered
• • Cumulus=puffyCumulus=puffy
also linked to elevationalso linked to elevation• • low, middle, high, and vertically developedlow, middle, high, and vertically developed
- - Alto = middleAlto = middle
also linked to precipitationalso linked to precipitation• • nimbo (-us) = rainnimbo (-us) = rain
sometimes linked to temperaturesometimes linked to temperature• • warm vs. cold cloudswarm vs. cold clouds
Cirrus Clouds - High CloudsCirrus Clouds - High Clouds• • "Feathers" or "Wisps" or small "Puffs""Feathers" or "Wisps" or small "Puffs"
• • almost always High cloudsalmost always High clouds
• • Usually Ice crystalsUsually Ice crystals- - a "mackerel"a "mackerel"sky with small,sky with small,puffed, cirruspuffed, cirrus
clouds known asclouds known ascirrocumuluscirrocumulus- - and almostand almostlayeredlayeredcirrostratuscirrostratuscloudsclouds
Perspective is everythingPerspective is everything• • from below, the low clouds look like stratusfrom below, the low clouds look like stratus
• • from above they look like cumulusfrom above they look like cumulus
• • in reality they are some combination of both!in reality they are some combination of both!
• • from below, the low clouds look like stratusfrom below, the low clouds look like stratus
• • from above they look like cumulusfrom above they look like cumulus
• • in reality they are some combination of both!in reality they are some combination of both!
- - three layersthree layersare visibleare visibleherehere- - cirrus cirrus > > v. highv. high- - altocirrusaltocirrus> > middlemiddle- - stratocumulusstratocumulus> > lowerlower
- - three layersthree layersare visibleare visibleherehere- - cirrus cirrus > > v. highv. high- - altocirrusaltocirrus> > middlemiddle- - stratocumulusstratocumulus> > lowerlower
Stratus clouds• layered clouds
• occur at all elevations
• can be thick and rain/snow producing
- Stratusclouds looklike a graysky
- these areNimbostratusclouds whichproduce rain
Cumulus• puffy clouds with somevertical development
- these cumulus cloud examplesdeveloped due to heating ofland which caused the air toheat and rise into cooler air
Cumulonimbus Clouds• continued vertical development will eventually lead to
Cumulonimbus clouds
- these produce heavy local rains, strong winds, andthunderstorms
• Characterized by a tall, often flat-topped, puffycloud form
Orographic lifting creating a lenticular cloud
Precipitation • includes rain,drizzle, freezing rain, snow,hail, ice pellets etc.
• occurs when the weight of the water whichhas condensed in the air overcomes theinfluences of the winds keeping it aloft
- falls under the influence of Earth's Gravity- velocity doesn't continue to increase
> air resistance slows it down as it falls- Max Velocity called Terminal Velocity
> varies with size of the water droplet
Precipitation • includes rain,drizzle, freezing rain, snow,hail, ice pellets etc.
• occurs when the weight of the water whichhas condensed in the air overcomes theinfluences of the winds keeping it aloft
- falls under the influence of Earth's Gravity- velocity doesn't continue to increase
> air resistance slows it down as it falls- Max Velocity called Terminal Velocity
> varies with size of the water droplet
• most precip forms by a processes known as
Bergeron process
• most precip forms by a processes known as
Bergeron process
Precipitation (2:2)• Rain = drops > 0.5 mm
• Drizzle = droplets ~ 0.2 & 0.5 mm
• Freezing rain = liquid water(sometimes supercooled) which fallsonto freezing (or near freezing)surfaces
• Snow = ice crystal in dendrites,plates, columns, or needles form
• Pellets = aka, sleet; water dropletsfreeze
• Hail = big ice pellets that have been"recycled" through a cloud severaltimes
• Rain = drops > 0.5 mm
• Drizzle = droplets ~ 0.2 & 0.5 mm
• Freezing rain = liquid water(sometimes supercooled) which fallsonto freezing (or near freezing)surfaces
• Snow = ice crystal in dendrites,plates, columns, or needles form
• Pellets = aka, sleet; water dropletsfreeze
• Hail = big ice pellets that have been"recycled" through a cloud severaltimes
Dew/Frost• saturated air near the ground gets cooledto the saturation point, and water collectson any surface available
- Frost is frozen condensation- Dew is liquid condensation
• Dewpoint is the temperature that the air mustbe cooled to (under constant pressure) to reachsaturation and cause condensation
• Dewpoint is the temperature that the air mustbe cooled to (under constant pressure) to reachsaturation and cause condensation
Fog• Essentially low level clouds
• created when air is heated orcooled in contrast to land or water
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