Atmosphere and Atmosphere and WeatherWeatherAP Environmental ScienceAP Environmental Science

Unit Four Unit Four Chapter SixChapter Six

Climate and Terrestrial BiodiversityClimate and Terrestrial Biodiversity

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

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Blowing in the Wind: A Story of Connections

• 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• Mesosphere• Stratosphere • Troposphere

AtmosphereLayers

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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

• 99% 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 Water (H2O, 0 - 7%), Ozone (O3, 0 - 0.01%), and Carbon Dioxide (CO2, 0.01-0.1%),

Weather: A Brief IntroductionWeather: A Brief Introduction

• Weather is a short-term atmospheric conditions Weather is a short-term atmospheric conditions in an area.in an area.

• Hours or daysHours or days

FrontsFronts• Warm FrontWarm Front

– Boundary between warm mass of air and the cooler Boundary between warm mass of air and the cooler air it replaces. air it replaces.

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

• Cold FrontCold Front– Advancing mass of cold air that stays close to the Advancing mass of cold air that stays close to the

ground ground – 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– Cooler,clear weather is the result.Cooler,clear weather is the result.

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Warm Front

Coolair mass

Warm air mass

Cool air mass

Anvil top

Warm air massCold Cold FrontFront

FrontsFronts• Stationary FrontStationary Front

– boundary of fronts boundary of fronts does not movedoes 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

Air PressureAir Pressure

• Changes in atmospheric pressure also affect Changes in atmospheric pressure also affect weatherweather

• 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

High pressure High pressure

• A high pressure air mass contains A high pressure air mass contains cool, densecool, dense air that warms as it descendsair that warms 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

Low pressure Low pressure

• A low pressure air mass produces A low pressure air mass produces cloudy, cloudy, stormystormy weather. weather.

• The center of the low rises due to the low The center of the low rises due to the low density of air.density of air.

• If condensation nuclei are present with cooler If condensation nuclei are present with cooler conditions, there will be rain.conditions, there will be rain.

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Moist surface warmed by sun

Flows toward low pressure,picks up moisture and heat

Warm,dry air

Hot, wetair

Falls, is compressed, warms Rises, expands, cools

Heat releasedradiates to space

LOWPRESSURE

HIGHPRESSURE

Cool, dryair

Condensationand

precipitation

HIGHPRESSURE

HIGHPRESSURE

LOWPRESSURE

LOWPRESSURE

HumidityHumidity• RelativeRelative humidity 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 expressed as a percentagepercentage

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

• the Earth has about the Earth has about 326 million326 million cubic miles of water cubic miles of water

• only about only about 3,1003,100 cubic miles of this water is in the cubic miles of this water is in the air as water vapor > clouds > precipitationair as water vapor > clouds > precipitation

www.rowcamp.com/photos.htm 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 % 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

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Precipitation• Air containing water vapor cools in atmosphere and

therefore condenses to form droplets of liquid water– Rain: liquid, falls, (sphere)

– Freezing Rain: occurs when drop touches frozen surface

– Sleet: ice pellets, begins as rain but enters air below freezing

– Snow: water deposits in hexagonal nuclei below freezing

– Snow Pellets: grains of ice,

– Hail: 5-190 mm in diameter, concentric rings of ice

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

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

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

pressurepressure• Coriolis effectCoriolis effect causes winds to spiral from 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

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

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)

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Figure 6-3Page 103

Descendingcool air

Severethunderstorm

Tornado forms whencool downdraft andwarm updraft of airmeet and interact

Risingwarm air

Severe thunderstormscan trigger a numberof smaller tornadoes

Risingupdraftof airWarm, moist air drawn in

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

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Figure 6-4Page 104 Rising winds exit

from the storm athigh altitudes.

The calm centraleye usually is about

24 kilometers(15 miles) wide.

Moist surface windsspiral in towards thecenter of the storm

Gales circle the eye at speedsof up to 320 kilometers

(200 miles) per hour.

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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– Average Temperature– Average Precipitation

• amount • distribution

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Climate

the average weather patterns for an area overa long period of time (30 - 1,000,000 years).

is

It is determined by

Average Precipitation Average Temperatureand

which are influenced by

latitude altitude ocean currents

and affects

where people live how people livewhat they

grow and eat

© 2004 Brooks/Cole – Thomson Learning

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

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.

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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

42Fall(sun aims directly at equator)

Summer(northern hemisphere

tilts toward sun)

Spring(sun aims directly

at equator)

23.5º Winter(northern hemispheretilts away from sun)

Solarradiation

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•

                                                                     

Milankovitch cyclesMilankovitch cycles

The basic premise of the The basic premise of the theory is that, as the Earth theory is that, as the Earth travels through space, travels through space, three separate cyclic three separate cyclic movements combine to movements combine to produce variations in the produce variations in the amount of solar energy amount of solar energy falling on the Earth. falling on the Earth.

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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

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Ocean 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.

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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.

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Animation

Click to view animation.

Ocean currents and climate animation.

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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.

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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.

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

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Click to view animation.

Animation

Air circulation interaction.

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The El-Niño The El-Niño Southern Southern OscillationOscillation

• Occurs every few years in the tropical East Pacific

• 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

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Wind

Movement ofsurface water

Diving birds

Nutrients

Upwelling

Fish

Zooplankton

Phytoplankton

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Click to view animation.

Animation

Upwelling along western coasts animation.

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Normal ConditionsCold water

Warm water

Thermocline

SOUTHAMERICAWarm waters

pushed westward

AUSTRALIA

EQUATOR

Surface windsblow westward

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El Niño Conditions Cold water

Thermocline

Warm water

Warm water deepens offSouth America

SOUTHAMERICA

Warm waterflow stoppedor reversed

AUSTRALIA

EQUATOR

Drought inAustralia andSoutheast Asia

Winds weaken,causing updraftsand storms

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El Niño

Unusually warm periods

Unusually high rainfall

Drought

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Natural Greenhouse effect

(a) Rays of sunlight penetratethe lower atmosphere andwarm the earth's surface.

(b) The earth's surface absorbs much of the incomingsolar radiation and degrades it to longer-wavelengthinfrared (IR) radiation, which rises into the loweratmosphere. Some of this IR radiation escapes into spaceas heat and some is absorbed by molecules ofgreenhouse gases and emitted as even longerwavelength IR radiation, which warms thelower atmosphere.

(c) As concentrations of greenhousegases rise, their molecules absorb andemit more infrared radiation, which addsmore heat to the lower atmosphere.

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Click to view animation.

Greenhouse effect interaction.

Animation

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Prevailing winds pick up moisture from an ocean.

On the windward side of a mountain range, air rises, cools, and releases moisture.

On the leeward side of the mountain range, air descends, warms, and releases little moisture.

Moist habitats

Dry habitats

Rain shadow effect

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Cell 3 South

Cold,dry air falls

Moist air rises — rain

Cell 2 South

Cool, dryair falls

Cell 1 South

Moistair rises,cools, andreleasesmoistureas rain

Cell 1 North

Cool, dryair falls

Cell 2 North

Moist air rises — rain

Cell 3 NorthCold,dry airfalls

Polar cap

Arctic tundra

60°

30°

0°

30°

60°

Polar cap

Evergreenconiferous forest

Temperate deciduousforest and grassland

Desert

Tropical deciduous forest

EquatorTropical rain forest

Tropical deciduous forest

DesertTemperate deciduousforest and grassland

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Biomes: Latitude and Altitude

67Dry woodlands and shrublands (chaparral)

Temperate grassland

Temperate deciduous forest

Boreal forest (taiga), evergreen coniferousforest (e.g., montane coniferous forest)

Arctic tundra (polar grasslands)

Tropical savanna,thorn forest

Tropical scrub forest

Tropical deciduous forest

Tropical rain forest,tropical evergreen forest

Desert

Ice

Mountains(complex zonation)

Semidesert,arid grassland

Tropic ofCapricorn

Equator

Tropic ofCancer

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Polar (ice)

Subarctic (snow)

Cool temperate

Warm temperate

Dry

Tropical

Highland

Major upwelling zones

Warm ocean current

Cold ocean current

River

69Temperate deciduous forest(Nashville, Tennessee)