24854 Hydrology Lecture 2
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Transcript of 24854 Hydrology Lecture 2
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EarthsAtmosphere
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ATMOSPHEREATMOSPHERE
CompositionCompositionNitrogen - 78%Nitrogen - 78%
Dilutes oxygen and prevents rapid burning at theDilutes oxygen and prevents rapid burning at the
earth's surface. Living things need it to make proteins.earth's surface. Living things need it to make proteins.
Nitrogen cannot be used directly from the air. The NitrogenNitrogen cannot be used directly from the air. The NitrogenCycle is nature's way of supplying the needed nitrogen forCycle is nature's way of supplying the needed nitrogen for
living things.living things.
Oxygen - 21%Oxygen - 21%Used by all living things. Essential for respiration. ItUsed by all living things. Essential for respiration. It
is necessary for combustion or burning.is necessary for combustion or burning.
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ATMOSPHEREATMOSPHERE
CompositionComposition
Argon - 0.9%Argon - 0.9%Used in light bulbs.Used in light bulbs.
Carbon Dioxide - 0.03%Carbon Dioxide - 0.03%
Plants use it to make oxygen. Acts as a blanket andPlants use it to make oxygen. Acts as a blanket and
prevents the escape of heat into outer space. Scientists are afraidprevents the escape of heat into outer space. Scientists are afraidthat the burning of fossil fuels such as coal and oil are addingthat the burning of fossil fuels such as coal and oil are addingmore carbon dioxide to the atmosphere.more carbon dioxide to the atmosphere.
Water Vapor - 0.0 to 4.0%Water Vapor - 0.0 to 4.0%
Essential for life processes. Also prevents heat loss fromEssential for life processes. Also prevents heat loss fromthe earththe earth
Trace gases - gases found only in very small amounts. TheyTrace gases - gases found only in very small amounts. Theyinclude neon, helium, krypton, and xenon.include neon, helium, krypton, and xenon.
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ATMOSPHEREATMOSPHERE
CompositionComposition
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ATMOSPHEREATMOSPHERE
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Earths atmosphere is made upEarths atmosphere is made up
of 5 different layersof 5 different layers
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Why is the atmosphere dividedWhy is the atmosphere divided
into 5 different layers?into 5 different layers? Any guesses?Any guesses?
The atmosphere is divided intoThe atmosphere is divided intofive different layers because thefive different layers because the
atmosphere is not uniform, itsatmosphere is not uniform, itsproperties change withproperties change withaltitude.altitude.
Two properties change withTwo properties change with
altitude, the AIR PRESSUREaltitude, the AIR PRESSUREand the AIR TEMPERATUREand the AIR TEMPERATURE
Lets look at each layerLets look at each layer
individually.individually.
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The first layer of the atmosphere isThe first layer of the atmosphere is
thethe
The troposphere is the layer of the atmosphere nearest toThe troposphere is the layer of the atmosphere nearest toearth.earth.
The troposphere goes from 0km to 16km.The troposphere goes from 0km to 16km. All weather happens in the troposphere.All weather happens in the troposphere. More than half the air in the total atmosphere is in thisMore than half the air in the total atmosphere is in thislayer.layer.
The temperature drops as the altitude increases.The temperature drops as the altitude increases.
Harmful ozone is found hereIT CREATES SMOG!Harmful ozone is found hereIT CREATES SMOG!
TROPOSPHERETROPOSPHERE
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What is OZONE?What is OZONE?
A gaseous layer in the upperatmosphere that protects theearth from harmful ultravioletradiation. At lower levels, ozonebecomes a major pollutant.
What is SMOG?What is SMOG? Pollution formed by the
interaction of pollutantsand sunlight(photochemical smog),usually restrictingvisibility, and occasionallyhazardous to health.
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The second layer of theThe second layer of the
atmosphere is theatmosphere is the The stratosphere goes fromThe stratosphere goes from16km to 50 km.16km to 50 km.
The temperature goes upThe temperature goes upwith altitude.with altitude.
Most jets fly in this layer.Most jets fly in this layer. The protective ozone is atThe protective ozone is atthe top of the atmosphere (Itthe top of the atmosphere (Itprotects us from theprotects us from theultraviolet radiation of theultraviolet radiation of thesun.)sun.)
Rivers of air, called JetRivers of air, called JetStreams, can be found at theStreams, can be found at the
base of this layer.base of this layer.
STRATOSPHERESTRATOSPHERE
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The third layer of the atmosphereThe third layer of the atmosphere
is theis the
The Mesosphere goes fromThe Mesosphere goes from50km to 90km.50km to 90km.
In the mesosphere, theIn the mesosphere, thetemperature drops withtemperature drops withaltitude.altitude.
The mesosphere is the coldestThe mesosphere is the coldestlayer of the atmosphere.layer of the atmosphere.
Meteors burn up in this layer.Meteors burn up in this layer. Radio waves are reflected backRadio waves are reflected backto earth in the mesosphere.to earth in the mesosphere.
MESOSPHEREMESOSPHERE
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The fourth layer of the atmosphereThe fourth layer of the atmosphere
is theis the
The thermosphere goes from 90km to 300km.The thermosphere goes from 90km to 300km. In the thermosphere the temperature goes up withIn the thermosphere the temperature goes up with
altitude.altitude. The thermosphere is the hottest layer of the atmosphere.The thermosphere is the hottest layer of the atmosphere. Curtains of light called auroras occur in this layer.Curtains of light called auroras occur in this layer. The Ionosphere is found in the thermosphere. This is theThe Ionosphere is found in the thermosphere. This is the
component of the thermosphere that makes the auroras.component of the thermosphere that makes the auroras.
THERMOSPHERTHERMOSPHER
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The last layer of the atmosphere isThe last layer of the atmosphere is
thethe
The exosphere is theThe exosphere is the
outermost layer of theoutermost layer of theatmosphere.atmosphere. The temperature inThe temperature inthe exosphere goes upthe exosphere goes up
with altitude.with altitude. Satellites orbit earthSatellites orbit earthin the exosphere.in the exosphere.
EXOSPHEREEXOSPHERE
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CLOUD PHYSICSCLOUD PHYSICS
Cloud physicsis the study of thephysical processes that lead to theformation, growth and precipitation ofclouds. Cloud formations are composedof microscopic droplets of liquid water(warm clouds), tiny crystals of ice (cold
clouds), or both (mixed phase clouds).
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FORMATIONFORMATION
The amount of water that can existas vapor in a given volume
increases with the temperature.When the amount of water vapor isin equilibrium above a flat surface
of water the level of vaporpressure is called saturation andthe relative humidity is 100%.
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FORMATIONFORMATION
At this equilibrium there are equalnumbers of molecules evaporating from
the water as there are condensing backinto the water. If the relative humiditybecomes greater than 100%, it is called
supersaturated. Supersaturation occursin the absence of condensation nuclei,for example the flat surface of water.
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FORMATIONFORMATION
Since the saturation vapor pressure isproportional to temperature, cold air
has a lower saturation point than warmair. The difference between these valuesis the basis for the formation of clouds.
When saturated air cools, it can nolonger contain the same amount ofwater vapor.
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FORMATIONFORMATION
If the conditions are right, theexcess water will condense out of
the air until the lower saturationpoint is reached. Anotherpossibility is that the water stays in
vapor form, even though it isbeyond the saturation point,
resulting in supersaturation.
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Supersaturation
Supersaturation of more than 12%relative to water is rarely seen in the
atmosphere, since cloudcondensation nuclei are usuallypresent. Much high degrees of
supersaturation are possible inclean air, and are the basis of
the cloud chamber.
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Supercooling
Water droplets commonly remain as liquidwater and do not freeze, even well below 0oC, because of the high surface tension of
each microdroplet, which prevents themfrom expanding to form larger ice crystals.Without ice nuclei supercooled liquid water
droplets can exist down to about 40C (40 F), at which point they willspontaneously freeze.
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Collision-coalescence
Droplets suspended in the air willinteract with each other, either by
colliding and bouncing off eachother or by combining to form alarger droplet. Eventually, the
droplets become large enough thatthey fall to the earth as
precipitation.
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Bergeron process
The Bergeron process notes thatthe saturation vapor pressure of water,
or how much water vapor a givenvolume can hold, depends on what thevapor is interacting with. Specifically,
the saturation vapor pressure withrespect to ice is lower than thesaturation vapor pressure with respect
to water.
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Bergeron process
Water vapor interacting with a water dropletmay be saturated, at 100% relative humidity,when interacting with a water droplet, but
the same amount of water vapor would besupersaturated when interacting with an iceparticle. The water vapor will attempt to
return to equilibrium, so the extra watervapor will condense into ice on the surfaceof the particle. These ice particles end up as
the nuclei of larger ice crystals.
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Bergeron process
The Bergeron process relies on supercooledliquid water interacting with ice nuclei toform larger particles. If there are few ice
nuclei compared to the amount of SLW,droplets will be unable to form
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Bergeron process
. A process whereby scientists seed a cloudwith artificial ice nuclei to encourageprecipitation is known as cloud seeding.
This can help cause precipitation in cloudsthat otherwise may not rain. Cloudseeding adds excess artificial ice nuclei
which shifts the balance so that there aremany nuclei compared to the amount ofsupercooled liquid water.
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Bergeron process
An overseeded cloud will form manyparticles, but each will be very small. Thiscan be done as a preventative measure for
areas that are at risk for hail storms.
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Dynamic phase hypothesis
The second critical point in the formation ofclouds is their dependence on updrafts. Asparticles group together to form water
droplets, they will quickly be pulled down toearth by the force of gravity. The dropletswould quickly dissipate and the cloud will
never form. However, if warm air interactswith cold air, an updraft can form. Warm airis less dense than colder air, so the warm airrises.
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Dynamic phase hypothesis
The air travelling upward buffers the fallingdroplets, and can keep them in the air muchlonger than they would otherwise stay.