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Integrated Science—Ch 17 Notes—The Weather
The Atmosphere
-relatively thin shell of gases that surround the solid Earth
-more gas molecules found near the surface
-atmosphere thins rapidly as the altitude/height increases
-Composition of the Atmosphere
-composed mostly of 3 gases
-Nitrogen—78%
-Oxygen—21%
-Argon—1%
-contains varying amounts of water vapor
-enters by evaporation and leaves as
precipitation
-N, O, Ar, and water vapor make up about 99.97% of the
volume
-remaining gases mostly CO2and traces of inert gases
-Carbon dioxide--.03%
-in addition to gases the atmosphere also contains particles of
dust,smoke,salt crystals, and
tiny solid or liquid particles called aerosols
-larger particles are not suspended as the aerosols are
and settle out of the atmosphere as dust or soot
-Atmospheric Pressure
-pressure decreases as altitude increases
-equalize pressure via the eustachian tube
-measured using a barometer
-Warming the Atmosphere
-radiation from sun must pass through the atmosphere
-atmosphere filters, absorbs, and reflects
incoming radiation
-on average Earth reflects about 30% of the total radiation
back to space
-about 2/3 due to clouds
-only about ½ of incoming radiation reaches Earth’s
surface
-reflection and selective filtering by atmosphere allow
global average of 240 watts per square meter
to reach surface
-wide variations occur with latitude
and season
-radiation that reaches surface is absorbed
-rocks, soil, water and ground become warmer
-emit absorbed solar energy as
infrared radiation (wavelengths
longer than visible light spectrum)
-infrared absorbed by water vapor and
Carbon dioxide causing increased
kinetic energy of molecules causing
increased temperature
-the more CO2 in the atmosphere the
more energy that will be redirected
back to Earth increasing the temp. near the
surface
-Greenhouse Effect--process of
heating the atmosphere by absorption of solar
radiation and reemission of infrared radiation
-Structure of the Atmosphere
-temperature decreases as altitude increases
-an average temperature decrease of 6.5 C for
every 1 km increase in height
-applies only to air not rising or
sinking
-Inversion--layer where temperature increases with
height
-often occur on calm winter days after arrival of
cold front
-stagnant mass of cold air may settle over an
area
-also occur on calm,clear , and cool
nights when surface rapidly loses radiant energy to
space
-results in a “cap” of cooler more dense air
overlying the warmer air beneath
-often leads to increased air pollution
because it prevents dispersion of pollutants
-temperature decreases with height until about
11 km (6.7 miles)
-Troposphere--layer from surface to where
temperature stops decreasing
-almost all weather occurs here
-Stratosphere--2nd layer above troposphere
-temperature increases with height
-less turbulent than troposphere—better for planes
-temperature gradually increases to about
48 km (30 miles)
http://www.foxnews.com/science/2013/10/23/antarctic-ozone-hole-hits
-Ionosphere--outermost layer
-where molecules merge with vacuum of space
-electrons and ions here responsible for reflecting
radio waves around Earth and for the
northern lights
-The Winds
-Troposphere heated from the bottom up as surface
of Earth absorbs sunlight
-Uneven heating of Earth’s surface sets stage for convection
-As local region of air becomes heated it expands and
becomes less dense
-less dense air is pushed upward by nearby cooler more dense
air
-Results in 3 general motions of air
1. Upward movement of air over a region of
greater heating
2. The sinking of air over a cooler region
3. Horizontal movement of air is wind
-direction is defined as the direction from
which it blows
-air in troposphere rises, moves as wind, and sinks
-all 3 movements related and all occur at the same
time over regions of the landscape
-during a day with gentle breezes on the surface, the
individual fluffy clouds form over areas where the air
is moving upward
-the clear are between the clouds is over areas where
the air is moving downward
-Local Wind Patterns
-2 factors important for understanding local wind patterns
1. The relationship between air temperature and
air density
-cool air has a greater density than a warm air
mass
-warm air is buoyed up by cool air
-results in upward,downward, and
horizontal movement of air called
a convection cell
2. The relationship between air pressure and
the movement of air
-upward movement of air produces a “lifting”
effect on the surface results in an area of lower
pressure
-downward movement produces a “piling up”
effect on the surface resulting in an area of
higher pressure
-air generally moves from an area of high
pressure to an area of low pressure
-Local wind patterns where land is next to water
-land and water have different heating rates and may
have different surface temperatures
-3 principle reasons for difference
1. The specific heat of water is greater
than that of soil
-equal masses of soil and water exposed to
sunlight—soil heats about 1 C while
water heats about ½ C
2. Water is a transparent fluid that is easily
mixed and spreads out the heating effect
-sunlight warms a relatively thin layer of
soil concentrating the heating effect
3. Water is cooled by evaporation, which
helps keep the body of water at a lower temp.
-results in warm air mass over land and a cooler
air mass over water
-cool air moves in from the ocean to the land
-Sea Breeze
-at night land cools more rapidly and the wind
direction reverses blowing out toward sea
-Local wind pattern due to Mountains
-mountain slope heated more than the valley because
it receives more direct sunlight
-cooler air from valley blows up the mountain slope
-Cold dense air can collect in valleys
-a weather disturbance or front can disturb
accumulation of cold air and cause it to pour
out of its resting place through canyons and
lower valleys
-air moving from high altitude to lower
altitude becomes compressed increasing its
kinetic energy and thus its
temperature
-Chinook wind—common to
mountainous regions—has sharp temp.
increases that can melt snow in a day
Global Wind Patterns
-apparent when records analyzed for long period of time
-Temperature imbalances drive global circulation of the
Atmosphere
-Earth receives more direct sunlight at equitorial regions than at
Higher latitudes
-temps. Of lower troposphere generally higher at
equitorial region and lower with latitude toward both poles
-the lower troposphere from 10 degrees N to 10 degrees S of
The equator is heated,expands, and becomes less dense
-hot air rises in this belt around the equator
-Intertropical Convergence Zone
-rising air cools resulting in heavy average
precipitation
-Tropical rainforests here
-the now dry, rising air reaches upper parts of the
troposphere and spreads north and south sinking back towards
the surface
-descending air reaches the surface to form a high
pressure belt that is centered about 30 N and 30 S of
the equator
-air moving away from this high pressure belt
produces the prevailing northeast trade
winds and the prevailing westerly winds
of the Northern hemisphere
-great deserts of Earth also located in
this high-pressure belt of descending dry air
-Poleward of the belt of high pressure the
atmosphere circulation is controlled by a powerful belt of
wind near the top of the troposphere called the jet stream
-Jet Stream--sinuous, meandering loops of
winds that tend to extend all the way around the Earth,
moving generally from the west in both
hemispheres at speeds up to 100 mi/h (160 km/h) or
more
-may occur as a single belt, or loop, of wind
but may divide into 2 or more parts
-develops North and South loops of
waves much like waves on a long rope
-waves vary in size
-waves bulge toward the poles(crests)
or toward the equator(troughs)
-warm air masses move toward poles
ahead of a trough and cool air masses
move toward the equator behind a
trough as it moves eastward
-the Intertropical Convergence Zone, the 30 degree belt of
high pressure, and the meandering jet stream all shift
toward or away from the equator during
different seasons of the year