24854 hydrology lecture 2

7/25/2019 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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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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CompositionComposition


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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.

24854 hydrology lecture 2

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