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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
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