1. The Atmosphere – Overview (Text Pg 4-14, 20-24)
Learning Outcomes:
Describe the constituents and the characteristics of the atmosphere along with common terms used to describe its features.
Describe the layers of the atmosphere based on temperature and why such a temperature structure exists.
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2. The Atmosphere - Characteristics
no specific top, 99 % below 30 km
moves and changes in time
expand, compress, cool, warm
most Wx in lower km
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3. Some Standard Definitions/Units
Weather (Wx): state of the atmosphere at a given time and place
Climate: represents accumulated Wx events over a period of time
Wind (Speed and Direction)
1 kts = 1.85 km/h = 0.51 m/s
South wind: wind blowing from South
Pressure (force/area) or (weight of air/area)
@sea level = 14.7 lb/in2 = mb = hPa (hectoPascals)
Density (mass of air molecules/volume)
Temperature (measure of molecule speed)
ºC = ºK (0 ºC = 273 Kelvin: absolute scale)
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4. Composition of Air Permanent Nitrogen (N2): 78% (by volume)
Creation: decaying bio matter,
Removal: bio procress (soil bacteria, plankton, plants)
Oxygen (O2): 21%
Creation: photosynthesis,
Removal: oxides, decaying bio matter, respiration
Argon<1%, Neon, Helium, Krypton, Hydrogen
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5. Composition cont’d Variable CO2 : 0.037%
Creation: veg decay, exhalation, combustion,
Removal: photosynthesis, dissolves in oceans
Methane (CH4), Ozone (O3), CFC’s, Aerosols (dust, soot, etc).
Water Vapour (H2O gas) : very important
Greenhouse Gases: CO2, H2O vapour, CH4, nitrous oxide, CFC’s
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6. CO2 Concentrations (Fig 1
CO2 Concentrations (Fig 1.4): Increasing (Natural Sources + Human Caused) CO2 Cycle (Fig 1.3) (Balance of Sources and Sinks)
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7. Composition cont’d - Aerosols
tiny particles, solid or liquid – sizes in microns (=micrometers) 1 m = 1/1000 th millimeter
Natural sources: volcanoes, fires, windblown dust
Human caused: combustion
dust ( m or larger)
PM2.5 : from combustion (< 2.5 m)
viruses (about < 0.01 m)
diameter of human hair (10 – 200 m)
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8. Water in the Atmosphere: Important
Water Vapour (H2O – gas): up to 4%, varies depending on time and location
Water: only substance in 3 states in atmosphere
Major influence on Wx
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9. Air Pressure and Height (Figure 1.7) and Figure 1.8

10. Layers of the Atmosphere (Temp – General Characteristic) (Fig 1.9)
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11. Vertical Structure of Atmosphere (Temperature) - Troposphere
lowest 11 km (average): most Wx
Temp decreases with height: ave of 6.5 C/1000 m in elevation (Environmental Lapse Rate)
warmest at surface: why?
capped by Tropopause (isothermal layer : Temp does not change with height)
transition layer, sometimes not evident
Tropopause height: lower at poles, higher at equator and varies seasonally: why?
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12. Vertical Structure of Atmosphere (Temperature) - Stratosphere
km ASL: O3 created here (O3 25 km)
temperature inversion – Temp increases with height
suppresses upward movement from Troposphere
O3 : absorbs Ultra Violet (UV) radiation (from Sun) - warms stratosphere– creates inversion
capped by Stratopause (isothermal layer)
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13. Vertical Structure of Atmosphere (Temperature) - Mesosphere
between km
air very thin (99.9% of mass is below)
little O3, so no UV absorbtion,
Temp decreases with height - why?
capped by Mesopause
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14. Vertical Structure of Atmosphere (Temperature) - Thermosphere/Exosphere
Thermosphere > 90 km
“Temp” increases with height
lots of energy input, few air molecules
molecules becomes very energetic,
Exosphere > 500 km
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15. Summary Atmospheric pressure:
at any level represents the total mass of air above that level
always decreases with increasing height above surface
Atmosphere: a mixture of gases, some of fixed amounts, others vary (H2O important)
Atmosphere: divided into layers (or regions) based on temperature structure
Troposphere: where the Wx happens
Stratosphere: O3 created - absorbs UV radiation which results in an inversion
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16. Websites of Interest – Wx Information
Balloon (Radiosonde) Soundings – Profile of Atmosphere
General Wx Info
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