Atmosphere and Atmosphere and WeatherWeather

AP Environmental ScienceAP Environmental Science

Mark Ewoldsen, Ph.D.Mark Ewoldsen, Ph.D.Dr. EDr. E

www.ai.mit.edu/people/jimmylin/pictures/2001-12-seattle.htm

Origin of Modern Atmosphere• original atmosphere surrounded the homogenous planet

Earth and probably was composed of H and He• second atmosphere evolved from gases from molten

Earth– H2O, CO2, SO2, CO, S2, Cl2, N2, H2, NH3, and CH4

– allowed formation of oceans and earliest life

• modern Atmosphere– evolved after Cyanobacteria started photosynthesizing

– oxygen produced did not reach modern levels until about 400 million years ago

www.degginger.com/digitalpage.html

• compared to the size of the Earth (104 km), the atmosphere is a thin shell (120 km).

Earth’s Atmosphere

http://www.gsfc.nasa.gov/gsfc/earth/pinatuboimages.htm

• Exosphere • Thermosphere• (Ionosphere)• Mesosphere• Stratosphere • Troposphere

AtmosphereLayers

Troposphere• 8 to 14.5 kilometers high (5 to 9 miles)

• most dense

• the temperature drops from about 17 to -52 degrees Celsius

• almost all weather is in this region

Stratosphere

• extends to 50 kilometers (31 miles) high• dry and less dense• temperature in this region increases

gradually to -3 degrees Celsius, due to the absorption of ultraviolet radiation

• ozone layer absorbs and scatters the solar ultraviolet radiation

• ninety-nine percent of "air" is located in first two layers

• every 1000-m 11% less air pressure

Composition

• Nitrogen (N2, 78%)• Oxygen (O2, 21%)• Argon (Ar, 1%)• myriad of other very

influential components are also present which include the Water (H2O, 0 - 7%), "greenhouse" gases or Ozone (O3, 0 - 0.01%), Carbon Dioxide (CO2, 0.01-0.1%),

Importance of the Atmosphere• Physicists

– physical properties and processes that take place between the radiant energy and atmospheric gases

• Chemists – behavior of the chemical materials in the

atmosphere• the ways in which lightning causes the formation

of substances • chemistry of the ozone layer and of chemicals

introduced from industrial processes

• Astronomers and space scientists – the layer through which they must peer

before entering the realms of space

• Meteorologists, climatologists and geographers– lower layers of the atmosphere

• predicting the weather• investigating climatic regions • examine the effects of climate and weather on

human society

REVIEW QUESTIONSWhat gas was originally not in What gas was originally not in the atmosphere?the atmosphere?

A. Carbon dioxideA. Carbon dioxide

B. Water B. Water

C. OxygenC. Oxygen

D. MethaneD. Methane

REVIEW QUESTIONSThe gas that composes 78% of The gas that composes 78% of the gases in the atmosphere is:the gases in the atmosphere is:

A. OxygenA. Oxygen

B. NitrogenB. Nitrogen

C. Carbon DioxideC. Carbon Dioxide

D. OzoneD. Ozone

REVIEW QUESTIONSThe atmosphere layer in which most The atmosphere layer in which most of the weather occurs is the:of the weather occurs is the:

A. TroposphereA. Troposphere

B. StratosphereB. Stratosphere

C. MesosphereC. Mesosphere

D. ThermosphereD. Thermosphere

E. ExosphereE. Exosphere

Seasonal ChangesSeasonal Changes

• Occur because the earth’s axis is tilted

• Creates opposite seasons in the northern and southern hemisphere

• Factor that determines global air circulation patterns

SEASONSSEASONS

• Seasons are short Seasons are short periods of climatic periods of climatic change.change.

• Because the Earth is Because the Earth is tilted, certain areas of tilted, certain areas of Earth receive changing Earth receive changing amounts of radiation amounts of radiation throughout the year.throughout the year.

Earth’s SeasonsEarth’s Seasons

North Pole

Earth

When the north pole tilts toward thesun, it gets more radiation – more warmth

during the summer

SUMMER (Northern Hemisphere)

South Pole

WINTER (Southern Hemisphere)

When the north pole tilts toward thesun, the south pole tilts away

So when it’s summer in the north, it’s winter in the south

Equato

r

Tilt of the Earth’s axis towards or away from the sun creates the seasons

Earth’s Seasons Continued….Earth’s Seasons Continued….

When the north pole tilts away from the sun, it gets less radiation –

So it’s colder during the winter

Earth

WINTER (Northern Hemisphere)

SUMMER (Southern Hemisphere)

When the north pole tilts away from thesun, the south pole tilts toward it…

When it’s winter in the north, it’s summer in the south

North Pole

South Pole

Equator

Ocean CurrentsOcean Currents• Sea-surface temperature influences

air temperature as the ocean exchanges heat with the overlying atmosphere.

• It also influences evaporation rates which are generally higher where sea-surface temperature is higher

Ocean CurrentsOcean Currents• There are two type of Ocean Currents:

• 1. Surface Currents--Surface Circulation

• These waters make up about 10% of all the water in the ocean.

• These waters are the upper 400 meters of the ocean.

Ocean CurrentsOcean Currents• 2. Deep Water Currents• These waters make up the other 90% of the

ocean• These waters move around the ocean basins

by density driven forces and gravity.• The density difference is a function of

different temperatures and salinity• These deep waters sink into the deep ocean

basins at high latitudes where the temperatures are cold enough to cause the density to increase.

Ocean CurrentsOcean CurrentsOcean Currents are influenced by two

types of forces1. Primary Forces--start the water moving

1. Solar Heating2. Winds3. Gravity4. Coriolis

2. Secondary Forces--influence where the currents flow

LATITUDELATITUDE•Latitude is the measure of the distance Latitude is the measure of the distance north and south of the equator. north and south of the equator. –Measured in degrees. Measured in degrees.

•Areas close to the equator, or 0 degrees Areas close to the equator, or 0 degrees latitude, receive the direct rays of the latitude, receive the direct rays of the sun. These direct rays provide the most sun. These direct rays provide the most radiant energy. radiant energy. –Areas near the equator are warm. Areas near the equator are warm. –Polar regions are cold.Polar regions are cold.

HIGH LATITUDESHIGH LATITUDESDuring the year, During the year, the high latitudes the high latitudes near the poles near the poles have great have great differences in differences in temperature and temperature and daylight hours. daylight hours.

Review Question

As latitude ________, the averageannual temperature _________.

0° Latitude 90°

Tem

per

atu

re

A.A. increases; increases; decreasesdecreases

B.B. decreases; decreases; increasesincreases

Air Temperature• As solar energy reaches the Earth, equatorial As solar energy reaches the Earth, equatorial

regions heat up more than the poles. regions heat up more than the poles.

• Warm air and water at the equator travel Warm air and water at the equator travel poleward while cold air and water at the poles poleward while cold air and water at the poles travel equatorward in an attempt to equalize this travel equatorward in an attempt to equalize this temperature contrast. temperature contrast.

• It is the atmosphere's continual struggle for It is the atmosphere's continual struggle for temperature balance that brings us our changing temperature balance that brings us our changing weather. weather.

http://www.usatoday.com/weather/tg/wglobale/wglobale.htm

Coriolis Effect

• The Earth is a spinning globe where a point at the equator is traveling at around 1100 km/hour, but a point at the poles is not moved by the rotation.

• This fact means that projectiles moving across the Earth's surface are subject to Coriolis forces that cause apparent deflection of the motion.

Coriolis Effect• Since winds are just molecules of air, they are also

subject to Coriolis forces.

• Winds are basically driven by Solar heating.

• Solar heating on the Earth has the effect of producing three major convection zones in each hemisphere.

• If solar heating were the only thing influencing the weather, we would then expect the prevailing winds along the Earth's surface to either be from the North or the South, depending on the latitude.

• However, the Coriolis force deflects these wind flows to the right in the Northern hemisphere and to the left in the Southern hemisphere.

Air PressureAir Pressure

• air pressure is caused by the weight of the air air pressure is caused by the weight of the air pressing down on the Earth, the ocean and on pressing down on the Earth, the ocean and on the air belowthe air below

• the pressure depends on the amount of air above the pressure depends on the amount of air above the measuring point and falls as you go higher the measuring point and falls as you go higher

• air pressure changes with weatherair pressure changes with weather

… … and Weatherand Weather

• air in a high pressure area compresses and air in a high pressure area compresses and warms as it descendswarms as it descends

• the warming inhibits the formation of clouds, the warming inhibits the formation of clouds, meaning the sky is normally sunny in high-meaning the sky is normally sunny in high-pressure areaspressure areas

• haze and fog might formhaze and fog might form

• the opposite occurs in an area of low pressurethe opposite occurs in an area of low pressure

http://www.usatoday.com/weather/tg/whighlow/whighlow.htm

HumidityHumidity• relative humidityrelative humidity is the amount of water vapor in is the amount of water vapor in

the air compared with the potential amount at the the air compared with the potential amount at the air's current temperatureair's current temperature– expressed as a percentageexpressed as a percentage

– depends on air temperature, air pressure, and water depends on air temperature, air pressure, and water availabilityavailability

• the Earth has about 326 million cubic miles of waterthe Earth has about 326 million cubic miles of water

• only about 3,100 cubic miles of this water is in the only about 3,100 cubic miles of this water is in the air as water vapor > clouds > precipitationair as water vapor > clouds > precipitation

www.rowcamp.com/photos.htm

Cloud cover• moisture in the atmosphere forms clouds which cover

an average of 40% of the Earth at any given time

• a cloudless Earth would absorb nearly 20 percent more heat from the sun

• clouds cool the planet by reflecting sunlight back into space. This is known as Albedo

However

• clouds reduce the amount of heat that radiates into space by absorbing the heat radiating from the surface and reradiating some of it back down

• the process traps heat like a blanket • “Cloud www.nasm.si.edu/earthtoday/ cloudlg.htm

• -Dec-2002 15:52:11 EST

http://worldbook.bigchalk.com/wbgifs/lr001421.htm

Precipitation• Air containing water vapor cools in atmosphere and

therefore condenses to form droplets of liquid water– Rain: liquid, falls, d >0.5 mm (sphere)– Freezing Rain: occurs when drop touches frozen surface– Sleet: ice pellets, d < 0,5 mm, begins as rain but enters air

below freezing– Snow: water deposits in hexagonal nuclei below freezing– Snow Pellets: grains of ice, d = 2-5 mm– Hail: 5-190 mm in diameter, concentric rings of ice

OTHER FACTORS THAT EFFECT PRECIPITATION:

-Prevailing winds

-Mountain ranges

REVIEW QUESTIONS•Humidity depends on:Humidity depends on:

A. air temperatureA. air temperature

B. air pressureB. air pressure

C. water availabilityC. water availability

D. All of the aboveD. All of the above

Winds• horizontal wind moves from areas of high horizontal wind moves from areas of high

to low pressure to low pressure • vertical wind moves from low to high vertical wind moves from low to high

pressurepressure• speed is determined by differences in speed is determined by differences in

pressurepressure• Coriolis effect causes winds to spiral from Coriolis effect causes winds to spiral from

high pressure zones and into low pressure high pressure zones and into low pressure zoneszoneswww.iiasa.ac.at/Admin/INF/OPT/ Spring98/feature_story.htm

Winds• wind speed is detected by a anemometer

and direction by a weather vane

• wind direction is based on where the wind is coming from: an wind from the east is an easterly

• Beaufort Wind Speed Scale is has a range from 0 for calm to 12 for a hurricane with waves greater than 37 feetwww.mountwashington.org/notebook/ transcripts/1999/07/07.htm

http://wings.avkids.com/Book/Atmosphere/Images/global_press.gif

FrontsFronts• Warm Front Warm Front

– separates warm air from the cooler air it moves into separates warm air from the cooler air it moves into (6 mph, NE)(6 mph, NE)

– rises over cool air massesrises over cool air masses– develops clouds and light precipitationdevelops clouds and light precipitation

• Cold FrontCold Front– cold air advancing into warm (9 to 30 mph, SE)cold air advancing into warm (9 to 30 mph, SE)– pushes under warm air – rising air just ahead of pushes under warm air – rising air just ahead of

frontfront– vertical movement strong and thus thunderstormsvertical movement strong and thus thunderstorms

FrontsFronts• Stationary FrontStationary Front

– boundary of fronts does not moveboundary of fronts does not move– generally due to winds running parallel to each other generally due to winds running parallel to each other

in two areasin two areas

• OccludedOccluded– where cold front overtakes warm frontwhere cold front overtakes warm front

Severe Weather - ThunderstormsSevere Weather - Thunderstorms• occur from equator to Alaskaoccur from equator to Alaska• may have hail, strong winds, lightning, thunder, rain &Z may have hail, strong winds, lightning, thunder, rain &Z

tornadoestornadoes• moist air rises due to frontal zone lifting causing loss of moist air rises due to frontal zone lifting causing loss of

heat leading to cumulus clouds with updraftsheat leading to cumulus clouds with updrafts• at 42,000 feet downdrafts and precipitation startat 42,000 feet downdrafts and precipitation start• may last an hourmay last an hour• severe thunderstorms occur when cold front approaches severe thunderstorms occur when cold front approaches

warm front (which supplies moisture and energy)warm front (which supplies moisture and energy)– winds over 60 mphwinds over 60 mph– hail > 3/4 inchhail > 3/4 inch

Severe Weather - Tornadoes• swirling masses of air with speeds of 300 mph+swirling masses of air with speeds of 300 mph+

• waterspouts occur over waterwaterspouts occur over water

• center of tornado is extreme low pressure which center of tornado is extreme low pressure which causes buildings to implodecauses buildings to implode

• destruction is usually less than 0.5 miles wide destruction is usually less than 0.5 miles wide and 15 miles longand 15 miles long

• tornado alley is from Texas to Indiana (usually tornado alley is from Texas to Indiana (usually trailer homes)trailer homes)

Severe Weather - Hurricanes• cause most property damage and loss of lifecause most property damage and loss of life

• winds speeds greater that 74 mph at the centerwinds speeds greater that 74 mph at the center

• begin over warm oceans of the tropicsbegin over warm oceans of the tropics

• solar insolation (water >80solar insolation (water >80ooF) provides energy F) provides energy for huge evaporation, cloud formation, and for huge evaporation, cloud formation, and atmospheric liftingatmospheric lifting

Thorpe, Gary S., M.S., (2002). Barron’s How to prepare for the AP Environmental Science Advanced Placement Exam

Severe Weather - Hurricanes• stagesstages

– separate thunderstorms over tropical oceanseparate thunderstorms over tropical ocean– cyclonic circulation which causes them to pick up cyclonic circulation which causes them to pick up

more more moisture and heat energy from oceanmore more moisture and heat energy from ocean– winds speeds of 23 to 40 mph lead to winds speeds of 23 to 40 mph lead to Tropical Tropical

DepressionDepression– Tropical StormsTropical Storms have lower pressure and higher have lower pressure and higher

wind speeds (40-75)wind speeds (40-75)

• center is the eye center is the eye

• rainfall may exceed 24 inches in 24 hoursrainfall may exceed 24 inches in 24 hours

The El-Niño The El-Niño Southern Southern OscillationOscillation

• Occurs every few years• ENSO’s occur when

the prevailing westerly winds weaken or cease and surface waters along the South and North American Coasts become warmer

• Upwellings of cold nutrient rich waters are suppressed

• Leads to declines in fish populations

ENSO events result from weakening of tropical Pacific atmospheric and oceanic circulation

Climatic connections carry these climate effects throughoutthe globe (e.g., El Niño creates warm winters in AK and lots of rain in California)

2.19

LA NINALA NINA• The opposite of el Nino is The opposite of el Nino is

La Nina.La Nina.• During La Nina, the winds During La Nina, the winds

blowing across the Pacific blowing across the Pacific are stronger than normal are stronger than normal and warm water and warm water accumulates in the western accumulates in the western Pacific. The water near Pacific. The water near Peru is colder.Peru is colder.

• This causes droughts in the This causes droughts in the southern United states and southern United states and excess rainfall in the excess rainfall in the northwestern Untied States.northwestern Untied States.

REVIEW QUESTIONREVIEW QUESTION• What causes droughts in the southern United What causes droughts in the southern United

states and excess rainfall in the northwestern states and excess rainfall in the northwestern Untied States?Untied States?–A. La NinaA. La Nina–B. El NinoB. El Nino

During which do westerly winds weaken or cease and During which do westerly winds weaken or cease and surface waters along the South and North American surface waters along the South and North American Coasts become warmer?Coasts become warmer?

- A. La NinaA. La Nina- B. El ninoB. El nino

ClimateClimate• Average long term

weather of an area– Seasonal variations

and weather extremes averaged over a long period (at least 30 years)

• 2 Main factors– Temperature– Precipitation

• amount • distribution

CLIMATE CONTINUED…CLIMATE CONTINUED…

Factors that effect temperature:

–Latitude

–Elevation

–Closeness to large bodies of water

ELEVATIONELEVATION

Closeness to Large Bodies of WaterCloseness to Large Bodies of Water

Water Water moderates the moderates the temperature temperature creating cooler creating cooler summers and summers and warmer warmer winterswinters

SHORT TERM CHANGES IN SHORT TERM CHANGES IN CLIMATECLIMATE• Some short-term changes may be the Some short-term changes may be the result of changes in ocean currents result of changes in ocean currents and global winds.and global winds.

• Ocean currents help transfer heat to Ocean currents help transfer heat to the atmosphere. This process the atmosphere. This process generates global winds. The global generates global winds. The global winds help move ocean currents. winds help move ocean currents.

• Any major change in an ocean current Any major change in an ocean current can cause a change in climate. El Nino can cause a change in climate. El Nino is an example. is an example.

THE RAIN SHADOW EFFECT

REVIEW QUESTIONHow does the Rain Shadow How does the Rain Shadow Effect affect climate?Effect affect climate?A.A.•Windward side: warm and dryWindward side: warm and dry

•Leeward side: cold and moistLeeward side: cold and moist

B. B. •Windward side: cold and moist Windward side: cold and moist

•Leeward side: warm and dryLeeward side: warm and dry

Review question

As elevation _________, the averageannual temperature __________.

Elevation

Tem

per

atu

re A.A. increases; increases; decreasesdecreases

B.B. decreases; decreases; increasesincreases