Transcript Understanding Weather and Climate Ch 1

Part 1. Energy and Mass
Chapter 1.
Composition and Structure of the
Atmosphere
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Introduction
The Atmosphere
A mixture of gas molecules, suspended
particles, and falling precipitation
The atmosphere strongly affects our day-today lives
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Meteorology
The study of the atmosphere and the processes
that cause “weather”
Climatology
Examines weather elements over long time
periods
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Variable Gases
Water Vapor
Most abundant variable gas
Added/ removed to air through the hydrologic
cycle
Concentrations = nearly 0% to nearly 4%
Important to energy balance and many
atmospheric processes
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Carbon Dioxide
A trace gas
• 0.038% of atmosphere’s mass
• Important to Earth’s energy balance
Added through biologic respiration, volcanic
activity, decay, and natural and human-related
combustion
Removed through photosynthesis
Increasing at a rate of 1.8 ppm/year
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Temporal increases due to human activities
Seasonal variations related to biological activity
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Ozone
Tri-atomic form of oxygen
Absorbs ultraviolet radiation
Chlorofluorocarbons (CFCs) destroy ozone
Destruction peaks over southern hemisphere
Antarctic circumpolar vortex limits latitudinal
mixing
• Leads to an O3 “hole”
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Vertical Structure of the Atmosphere
Density
Mass (kg) per unit volume (m3)
• Sea level average = 1.2 kg/m3
Near surface air is more dense
• Compressibility
• Mean free path
– At surface = 0.0001 mm
– At 150 km = 10 m
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Compressibility of
gases relates to
density
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Thermal Layers of the Atmosphere
Four distinct atmospheric layers
• Troposphere
• Stratosphere
• Mesosphere
• Thermosphere
Each has particular temperature characteristics
with height.
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Troposphere
Lowest layer
Steady temperature decrease with height
• -6.5oC/km (-3.6oF/1000ft)
Virtually all weather processes
• Contains 80% of atmospheric mass
Tropopause = top of troposphere
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Violent updrafts may
penetrate cloud tops
into the
stratosphere. The
flattened
top of this
cumulonimbus
cloud is in the
stratosphere.
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Stratosphere
Little actual “weather”
Temperature inversion
• Caused by absorption of UV radiation by O3
Stratopause = top of stratosphere
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Mesosphere and Thermosphere
Combined = 0.1% of total mass
The mesosphere
• Decreasing temperatures with height
• Coldest layer
The thermosphere
• Slowly merges into space
• Increasing temperatures with height
– “Temperature” = molecular kinetic
energy
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Some Weather Basics
Weather information is abundant
Pressure and wind
Wind = horizontal movement of air
• Caused by unequal pressures
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Pressure units
• Millibar (mb), Kilopascal (kPa)
• Isobars
Station Models
• Portray weather information
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Temperature
Most obvious weather component
• Fronts
Humidity
May be expressed as relative humidity
• Dew point temperature
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