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Lesson 01 Atmospheric Structure

Lesson 01 Atmospheric Structure. Composition, Extent & Vertical Division. Composition. By Volume Nitrogen (N 2 ) 78% Oxygen (O 2 ) 21% Others (1%) Carbon Dioxide (CO 2 ) 0.035% Ozone + Others(Neon, Xenon etc) Water Vapour (variable from 0 - 4% locally). Composition con’t.

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Lesson 01 Atmospheric Structure

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  1. Lesson 01Atmospheric Structure • Composition, Extent & Vertical Division

  2. Composition • By Volume • Nitrogen (N2) 78% • Oxygen (O2) 21% • Others (1%) • Carbon Dioxide (CO2) 0.035% • Ozone + Others(Neon, Xenon etc) • Water Vapour (variable from 0 - 4% locally)

  3. Composition con’t • Analysis reveals no variation in its composition up to at least 60km • except for increasing concentrations of Ozone in the upper Stratosphere. • At higher altitudes, the force of gravity being less causes the proportions to change.

  4. Composition con’t • None of these gases changes its state within the normal temperature range of the atmosphere so dry air remains invisible. • Only water vapour changes its state • water  gas solid

  5. The water cycle, illustrating evaporation, condensation & precipitation

  6. The 3 M’s:- • Moisture • Mass • Movement

  7. Properties of the Earth’s Atmosphere • The earth’s atmosphere varies both vertically and horizontally in terms of: - Pressure - Temperature - Density - Humidity

  8. Properties of the Earth’s Atmosphere, contd. • The atmosphere is also a poor conductor of heat and being a gas is extremely fluid and only supports life in the lower levels. Fifty percent of the atmosphere is below the 500mb pressure level (about 18,000 feet).

  9. Vertical Division • The atmosphere extends to about 1000 km above the earth’s surface and • consists of several layers, each with its own properties. • The layers are defined by the temperature profile as shown in the following diagram..

  10. Vertical Division Ionosphere

  11. Troposphere • Layer in contact with surface • Contains 80% of atmosphere • Temperature decreases with height • Until Tropopause reached • Zone of vertical mixing by convection and turbulence • Contains most of water vapour • Zone of clouds and weather • Heated from below

  12. Tropopause • Indicated by marked change in lapse rate • Upper limit of cloud and weather • Lowest tropospheric temperatures at this level • Strongest winds aloft just below it • Height varies according to season and latitude • H2O decreases, O3 increases

  13. Typical Average Tropopause Heights and Temperatures

  14. Variation in Height of Tropopause • The thickness of the Troposphere will vary according to temperature. • Lower when the air is cold (i.e. polar latitudes) • Higher when air is warm (i.e. equatorial latitudes) • Height therefore depends on season and latitude • Coldest tropopause temperatures over the equator • Breaks in tropopause caused by jet streams

  15. Variation of Surface Pressure with Height of Tropopause • High tropopause • high air column • high surface pressure • more prevalent in summer • near equator • Low tropopause • low air column • low surface pressure • more prevalent in winter • near polar latitudes

  16. Height/temperature graph for tropopause JA, JB, JC = Jetstreams

  17. Layered structure defined by the temperature profile (ELR) through the atmosphere. (Radio sounding)

  18. Radio Sonde

  19. Stratosphere • Temperature increases with height to about 50 km. • Contains warm Ozone region in upper levels at 40-50 km. • Weather does not penetrate but some severe CB’s may penetrate several 1000’s of feet. • Nacreous clouds form at about 20-30 km

  20. Nacreous Clouds

  21. Stratopause • Marks upper limit (50 km), of the stratosphere. • Maximum temperature just below freezing.

  22. Mesosphere • Region of decreasing temperature • Noctilucent clouds form at approximately 80 - 85 km. • Usually visible in summer in Northern sky near midnight.

  23. Noctilucent Cloud North Ayrshire Scotland 1988 July 02-03 00005 UTC

  24. Mesopause • Marks the upper limit of the Mesosphere. • Height approximately 80-90 km. • Temperatures between -120°C (summer) & -50°C (winter) at high latitudes

  25. Thermosphere • Zone of increasing temperature • Upper limit undefined. • Merges into the Exosphere/Ionosphere.

  26. 90% of Ozone found here. Absorbs harmful Ultra Violet (UV) radiation. UV Radiation causes skin cancers. destroys DNA molecules. Ozone filters in aircraft Strongly absorbs IR earth radiation Absorbed energy re-radiated back to earth Helps maintain the thermal balance in the atmosphere Ozone in the Stratosphere

  27. Ozone Production • Ozone produced by interaction of molecular O2 and UV radiation • O2 + UV  O + O • O2 + O  O3 • Ozone forms mainly above 25 km but drifts down producing a peak concentration at 25 km.

  28. Ozone Destruction • Ozone is also destroyed by UV radiation. • O3 + UV  O2 + O • O3 + O  2O2 • Ozone is also destroyed by the collision between two ozone molecules. • O3 + O3  3O2

  29. Ozone Balance • Ozone between 25 and 35 km is maintained by a delicate natural balance • Ozone can be reduced by natural events e.g. solar flares and cosmic rays. • Pollutants such as fluorocarbons also destroy ozone.

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