Chapter 1 - Weather Underground

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Chapter 1: The
Earth’s Atmosphere
What is Meteorology?
 Weather vs. climate
 Earth’s atmosphere
overview

What is Meteorology?
• First defined by Aristotle in Meteorologica
• Meteors used to be everything that fell from the sky
• Now, meteorology is the study of the atmosphere and its
phenomena
Weather and Climate
• What is weather?
• What is climate?
What Is Weather?
• Weather is the condition of the atmosphere at any
given time
• The temperature is 86°F
• The sky was cloudy this morning
• Remember in 1983 when it poured at the baseball
game?
Elements of Weather






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Air temperature
Air pressure
Humidity
Clouds
Precipitation
Visibility
Wind
• Certain weather elements, like
clouds, visibility and wind, are
of particular interest to pilots.
What Is Climate?
• The study of weather over a long period of time
• The average temperature for today is 86°F
• San Francisco is usually cloudy in August
• It usually rains during 15 baseball games a year
Climate


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Average weather
Extremes
“What usually happens”
Weather and Climate in Our
Lives

Wind chill, cold weather
Fig. 1-16, p. 19
Weather and Climate in Our
Lives

Crop damage from cold weather, freeze
Weather and Climate in Our
Lives

Hot weather, drought, heat stroke
Weather and Climate in Our
Lives

Hot weather, drought, heat stroke
Weather and Climate in Our
Lives

Severe thunderstorms, tornadoes, flooding
Weather and Climate in Our
Lives

Severe thunderstorms, tornadoes, flooding
Overview of the
Earth’s Atmosphere
Credit: NASA
Composition of the
Atmosphere

•
Two category of gases
Permanent
•
•
Output balanced by input
Variable
•
Output and input not always balanced in time
and place
Table 1-1, p. 3
Source and Removal of
Nitrogen (N )
2



Abundant because mainly inert
Removed by soil bacteria, ocean plankton
Source is from decaying plants and
animals, volcanoes
Source and Removal of
Oxygen (O )
2




Removed when plant and animals decay
Removed in chemical processes when
oxygen combines with other stuff
Removed during breathing
Source is from plants during
photosynthesis (CO2 + water = sugar and
oxygen)
Source and Removal of Water
Vapor (H O vapor)
2


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Very, very important
Varies greatly in place and time
Only substance in lower atmosphere as
gas, liquid, and solid
Removed when precipitation falls to
surface
Source is from evaporation, sea wind
Source and Removal of
Carbon Dioxide (CO )
2

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Occupies small portion of atmosphere
Removed during photosynthesis. CO2 is
stored in roots and branches
Removed by the oceans (massive storage
- 50 times atmospheric content)
Source is burning of fossil fuels (stored
CO2), deforestation, vegetation decay,
exhalation, volcanoes
Past measurements come from ice cores
Fig. 1-4, p. 5
Two-faced Ozone (O )
3

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Largest concentration in the stratosphere
(above 10 km)
Forms when oxygen atoms combine with
oxygen molecules
Good in upper atmosphere, absorbs
ultraviolet radiation
Bad near the surface, irritates eyes and
throats. Main ingredient of photochemical
smog
Other Stuff in the Atmosphere

Aerosols
•
•
•

Ash from volcanoes
Salt from wind blown saltwater
Dust from wind (dust devils)
Pollutants
•
Nitrogen dioxide, carbon monoxide,
hydrocarbons, sulfur dioxide
A Changing Atmosphere

The earliest atmosphere
•
•

Most likely made of of hydrogen and helium
So light they escaped to space
Subsequent atmosphere
•
•
Volcanoes put gas, outgassing, (water vapor,
CO2, and some Nitrogen) into environment
Water vapor produced rain for thousands of
years, CO2 into oceans, Nitrogen abundant
A Changing Atmosphere
•
Oxygen increased due to the development
of plants
How Is the
Atmosphere
Structured?

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What is above our heads?
Vertical temperature profile
Where does the weather
happen?
Air Pressure and Air Density

Air density (weight per volume)
•

Air pressure (force per area)
•
•

Gravity holds molecules to surface (most
dense near surface)
Always decreases with height
Air pressure changes with changing air
density
Sea-level pressure
•
Atmospheric standards (14.7 lbs per square
inch=1013.25 mb=29.92 inch Hg)
Fig. 1-7, p. 8
Fig. 1-8, p. 9
Layers of the Atmosphere

Temperature vertical profile more
complicated
Troposphere

Temperature generally decreases
with height
Cools due to sun heating surface
Temperature increasing with
height is called an inversion
Contains all weather we know

Great vertical movement
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Stratosphere
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Is characterized by increasing air
temperature
Height of tropopause varies in
height
Ultraviolet light is absorbed in the
stratosphere, warming the layer
Very limited vertical development
Mesosphere

Temperature decreases rapidly
once again

Air very thin
Thermosphere

Air temperature warms
once again due to
absorption of the sun by O2

Just a small amount of
absorption leads to warming
The Ionosphere


Electrified regions of the atmosphere
D, E, and F regions
D region is efficient at absorbing AM radio
waves, thus these waves don’t travel very far
 But, at night, the D region dissipates, allowing
for AM waves to bounce off the E and F
regions

Fig. 1-11, p. 13
A Satellite’s View of the
Weather

Geostationary satellites
• Atmospheric observation
from satellites was an
important technological
development in
meteorology. Other
important developments
include computers, internet,
and Doppler radar.
Storms of All Sizes
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Mid-latitude cyclonic storms – storms that
occur outside the tropics
Hurricanes and tropical storms – very
powerful storms that feed off of warm
water
Thunderstorms – very common during
Spring
Tornadoes – spawned from “Supercell
Thunderstorms”
A Look at a Weather Map

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Wind speed and direction
Cyclones and anticyclones
Fronts
• Wind direction is defined in the opposite way as
ocean currents: a southerly current means water is
moving towards the south.
Fig. 1-13, p. 17
A Satellite’s View of the
Weather

Current view
• Satellite view
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