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Chapter 15
Atmospheric Science
This lecture will help you understand:
The Earth’s atmosphere
Weather
Outdoor pollution and solutions
Stratospheric ozone depletion
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
The atmosphere
Atmosphere = the thin layer of gases that
surrounds Earth
– Absorbs radiation and moderates climate
– Transports and recycles water and
nutrients
– 78% nitrogen gas, 21% oxygen gas, 1%
other gases
• Water, ozone, carbon dixoide
– Its four layers differ in temperature,
density and composition
Minute concentrations of permanent (remain
at stable concentrations) and variable gases
(varying concentrations)
Human activity is changing the amounts of
some gases
Importance of the Atmosphere
Physicists
– physical properties and processes that take
place between the radiant energy and
atmospheric gases
Chemists
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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
The atmosphere’s composition
Atmosphere
Layers
Exosphere
Thermosphere
(Ionosphere)
Mesosphere
Stratosphere
Troposphere
The first layer of the atmosphere
Troposphere = bottommost layer
– Tropein: to change (Gr)
– Air for breathing, weather patterns
– Temperature declines with altitude
– Tropopause = limits mixing between
troposphere and the layer above it
The first next of the atmosphere
Stratosphere = 11-50 km (7-31 mi) above sea
level
– Drier and less dense, with little vertical
mixing
– Colder in its lower regions
– Contains UV radiation-blocking ozone, 1730 km (10-19 mi) above sea level
• Protects life on Earth’s Surface
The two highest levels of the atmosphere
• Mesosphere = 50-80 km (31-56 mi) above
sea level
– Middle
– Extremely low air pressure
– Temperatures decrease with altitude
• Thermosphere = atmosphere’s top layer
– Extends upward to 500 m (300 mi)
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The atmosphere’s four layers
Atmospheric properties
Atmospheric pressure = measures the force
per unit area produced by a column of air
– Decreases with altitude
Relative humidity = the ratio of water vapor
a given volume of air contains to the amount
it could contain at a given temperature
Temperature = varies with location and time
Solar energy heats the atmosphere
The spatial relationship between the Earth and
sun determines the amount of solar energy
striking the Earth
Energy from the sun
– Heats air
– Moves air
– Creates seasons
– Influences weather and climate
Solar radiation is highest near the equator
Albedo Effect
Surfaces that reflect energy have a high
albedo
– Snow, ice, sand
Surfaces that absorb energy have a low albedo
– Appear dark
– Black soil, pavement, open water, green
vegetation
The fate of solar radiation
Air Circulation in the Atmosphere
More of the sun’s rays strike the equator than
the poles
The tilt of the Earth’s axis
The Coriolis effect
Solar energy creates seasons
• Because the Earth is tilted
– Each hemisphere tilts toward the sun for
half the year
– Results in a change of seasons
– Equatorial regions are unaffected by this
tilt, so days average 12 hours through the
year
– When the Northern Hemisphere is in
summer, the Southern is in winter
– The sun rises and sets just once a year at
the Poles- 6 months of the year are
daytime and 6 are nighttime
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Global wind patterns
The atmospheric cells interact with Earth’s
rotation to produce global wind patterns
– As Earth rotates, equatorial regions spin
faster
Coriolis effect = caused by earth’s
rotational forces
– the north-south air currents of the
convective cells appear to be deflected
from a straight path
– Results in curving global wind patterns
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.
Climate patterns and moisture distribution
The atmosphere drives weather and climate
Weather = specifies atmospheric conditions
over short time periods and within a small
geographic areas
Climate = describes patterns of atmospheric
conditions across large geographic regions
over long periods of time
Mark Twain said “Climate is what we
expect; weather is what we get”
Solar energy causes air to circulate
Air near Earth’s surface is warmer and
moister than air at higher latitudes
• Convective circulation = less dense, warmer
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air rises and creates vertical currents
– Rising air expands and cools
– Cool air descends and becomes denser,
replacing warm air
– Influences both weather and climate
Air Currents
Air currents flow from regions of high
pressure to low pressure
Air masses produce weather
• Front = the boundary between air masses that
differ in temperature, moisture, and density
• Warm Front = the boundary where warm
moist air replaces colder, drier air
• Cold Front = the boundary where colder,
drier air displaces warmer, moister air
Air masses have different atmospheric pressures
• High-pressure system = air that moves away
from a center of high pressure as it descends
– Brings fair weather
• Low-pressure system = air moves toward the
low atmospheric pressure at the center of the
system and spirals upward
– Dew point: the temperature at which water
vapor condenses into liquid water
– Clouds and precipitation
Thermal inversion
• Usually, tropospheric air temperature
decreases as altitude increases
– Warm air rises, causing vertical mixing
• Thermal inversion = a layer of cool air
occurs beneath a layer of warmer air
– Inversion layer = the band of air in which
temperature rises with altitude
– Denser, cooler air at the bottom of the
layer resists mixing
– Sparked London’s “killer smog”
Coriolis Effect and Wind
• 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
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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.
Global Air Circulation and Biomes
Wind patterns
People used these winds to sail their ships
across the ocean
Doldrums = near the equator
– Few winds
– ITCZ: Intertropical Convergence Zone:
produces very heavy precipitation
Trade winds = between the equator and 30
degrees latitude
– Named for their ability to propel trading
ships across the ocean
– Blow from east to west
AKA: “horse latitudes” :30-35 degrees north
and south
– Very weak winds
Westerlies = from 30 to 60 degrees latitude
– Originate from the west and blow east
Polar easterlies= 60 degrees latitude to the
poles
• Jet stream: high-speed currents of wind that
occur in the upper trophosphere that influence
local weather patterns
Earth’s Rotation and Climate
Hadley Cells