ch.17 notes mc neely 2009

The AtmosphereCh. 17

Earth-Space Science

Bremen High School

Teacher: Aaron McNeely

Weather and Climate(Sec 17.1)

Earth’s Atmosphere: The gases that surround the earth Where weather occurs

Weather: The state of the atmosphere at a given place or time

Climate is based upon observations of weather over many years

Climate helps describe a place or region

Composition

Air is a mixture of different gases and particles

Contents: Nitrogen (78%) Oxygen (21%) Argon and others (1%)

Slice of Atmosphere?Nitrogen 78%

Oxygen 21%

CO2, Argon, Others

1%

Other Components

Water vapor, source of all clouds and precipitation

Ozone, form of oxygen (O3) that protects surface from sun’s ultraviolet light

Pollution

Artificial gases and particles placed into the atmosphere

About half consists of automobile exhaust

Height of the Atmosphere

Thins rapidly with height, also pressure Atmospheric pressure is the actual

weight of the atmosphere resting over your head

Rapid change in elevation can create uncomfortable pressure changes (ear popping)

Pressure vs. Altitude (height)

Pressure lies along the bottom axis, altitude along the vertical

Below how many miles is roughly half of the atmosphere?

Atmospheric Layers

The atmosphere is divided into four vertical layers based upon temperature changes

4 Layers: Troposphere Stratosphere Mesosphere Thermosphere

http://www.epa.gov/air/oaqps/eog/course422/images/fig-1.gif

Troposphere

Bottom layer Temperature decreases with height Height: 0-7 miles Tropopause: Boundary between

troposphere and stratosphere Where most of our weather occurs

Stratosphere

Second layer Temperature remains constant, then

increases with height Height: 7-30 miles Stratopause: Boundary between the

stratosphere and mesosphere The “ozone layer” lies at a height of 15 miles

within the stratosphere

Mesosphere

Third layer of the atmosphere Temperature decreases with height Height: 30-50 miles Mesopause: Boundary between the

mesosphere and Thermosphere

Thermosphere

Lat layer, gradually merges into outer space

Temperature increases with height Height: 50-90 miles The aurora or northern lights occur in

the thermosphere

Atmospheric Temperature Change

Temperature lies along the bottom axis, height along the vertical

The behavior of temperature defines each of the atmospheric layers

Layers Summary

Select the appropriate letter in the figure to the right that identifies each of the following layers of the atmosphere:

_____ mesosphere _____ troposphere _____ thermosphere _____ stratosphere

Earth-Sun Relationships

Earth’s Motions: Earth has two principal motions: Rotation: Earth’s 24 hour spin on its axis,

results in the day Revolution: Earth’s 365 day journey

around the sun, results in the year

Rotation & Revolution

http://geography.uoregon.edu/shinker/geog101/lectures/lec02/lec02_figs/Earth-revolution-and-rotation-fig2-13.gif

Earth’s Seasons

http://www.uwsp.edu/geo/faculty/ritter/images/atmosphere/energy/earth_orientation_small.jpg

Northern hemisphere directed towards the sun

Northern hemisphere directed away from the sun

Seasons

The seasons begin with events named solstices and equinoxes

Winter and Summer, the most extreme of the seasons, are solstices

Spring and Autumn, the “middle” seasons, are equinoxes

Season Summary

Event Season (North & south)

Sun Overhead (latitude)

Mar 21 Equinox

Spring (N)

Autumn (S)

Equator (0)

June 21 Solstice

Summer (N)

Winter (S)

Tropic of Cancer (+23.5)

Sept 21 Equinox

Autumn (N) Spring (S)

Equator (0)

Dec 21 Solstice

Winter (N)

Summer (S)

Tropic of Capricorn (-23.5)

Seasons Summary

Select the appropriate letter in the figure below that identifies each of the following months:

_____ March _____ June _____ December _____ September

Earth’s Orientation & Seasons

Earth tilted 23.5° compared to the sun Earth’s axis tilted compared to its orbit Tilt results in the northern and southern

hemispheres of earth each being directed toward the sun at different times during the year

Tilt is cause of earth’s seasons Axis will always point to the star Polaris

(North Star) in our lifetimes

Earth’s Tilted Axis

Geography: Seasons

Length of Day & Night

Changes due to earth’s tilt and revolution

Equinoxes, both day and night are 12 hours

Summer solstice, more hours of day, less of night

Winter solstice, less hours of day, more of night

Day & Night Hours

http://odin.physastro.mnsu.edu/~eskridge/astr101/day_night.jpg

Midnight

Noon

Days

Earth’s Tropics

The two Tropics lie 23.5° north and south of the equator

Latitudes where the noon sun is directly overhead during summer and winter

At the equinoxes, the noon sun lies directly overhead at the equator

Arctic & Antarctic

Arctic and Antarctic circles both lie 90°-23.5° = 66.5° north and south

Areas greater in latitude of the circles can experience 24 hours of day and night depending on the seasons

Tropics and Circles

Equinoxes

Planetary Positions

In elliptical orbits Perihelion: Position closest to sun Aphelion: Position farthest from sun Earth

Perihelion: Jan 02 Aphelion: July 04

Elliptical Orbit (Keplerian)

Sun

Earth

Oval in diagram is very exaggerated,

earth’s orbit is close to circular

Earth’s Revolution

At perihelion, earth revolves faster in its orbit, slower at aphelion

Sun’s apparent size changes slightly as a result

Close and Far

Climate Factors(Sec 17.3)

The main determinant of climate is latitude

Closer to equator, warmer climate Other:

Large bodies of water Altitude Cloud cover Ocean currents

Land and Water

Land heats rapidly and to higher temperatures compared to water

Land also cools rapidly and to lower temperatures than water

Marine locations have a nicer climate Southern Hemisphere: More ocean

than land creates moderate climates

Ocean vs. Land

Hemispheres

N

SE

W

Altitude

Higher elevations experience a cooler climate compared to locations near sea level

High and Low Altitude

Cloud Cover

Albedo: The fraction of total radiation that is reflected by a surface

Clouds have high albedos Cloud cover creates a cooler day, a

warmer night In day, clouds provide shade At night, clouds prevent the heat from

escaping into space

Cool Days, Warm Nights

Cloudy skies create cooler days and warmer nights

Urban Heat Islands

Cities are often 6-8º warmer than surrounding countryside

Reasons: Less green plants Concrete structures and roads absorb

heat, release slowly at night

Wash DC Urban Heat Island

Urban Heat Island Profile

World Temperatures

Isotherms are lines on a weather map connecting points of equal temperature

Temperatures generally range east to west, parallel to latitude

Temps decrease from equator to poles

Isotherms

•The lines generally trend west to east, and cooler from south to north

http://www.learner.org/jnorth/images/graphics/u-z/weather_isotherm030201.gif

Ocean Isotherms

https://www.fnmoc.navy.mil/products/OTIS/US058VMET-GIFwxg.OTIS.glbl_sst.gif