Science 010 - Fall, 1995

Lecture 3 - Sept 19

Physical Structure and Regions of the Atmosphere

  1. Pressure decrease with height

    a) Ignore the fact that the atmosphere is made up of a variety of gases and water vapour

    b) Treat atmosphere as an ideal gas - Ideal Gas Law

    c) Gas molecules tend to distribute uniformly to reduce pressure differences

    d) Gravity opposes this uniform distribution

    e) Balance of forces leads to pressure decreasing exponentially from the earth's surface to interstellar space.

    f) Consideration of gases of different molecular weights leads to distribution of constituents, in higher elevations. Convection at low elevations leads to homogeneity. Can broadly classify these two regions as heterosphere and homosphere.


  2. Temperature variations with height

    a) Another basis of classification - complicated behavior due to properties of the different regions

    b) In troposphere, temperature decreases linearly

    c) Explain this in terms of adiabatic expansion of an ideal gas


  3. Other regions

    a) Troposphere - location of weather phenomena. Contains 4/5 of total air mass. In this region, temperature decreases linearly with height.

    b) Stratosphere - ozone is produced here (more later) and protects us from UV rays from sun (more later). Temperature increases gradually through this region due to absorption of radiation.

    c) Mesosphere - temperature decreases here

    d) Thermosphere - temperature increases here as short wavelength radiation from the sun is absorbed by atoms or molecules that become ionized or dissociated

    e) Upper levels are also called the ionosphere due to large amounts of ionized particles. Concentration increases during the day, impairing radio reception as radio waves are absorbed by the ions rather than reflected.


    Assignment for Lecture 3 - September 19

    1. Calculate the number of gas molecules in one cubic meter at

      (a) sea level

      (a) 1 km above sea level, and

      (a) 10 km above sea level

    2. Compare the mass of the atmosphere located within 1 km of sea level to that of the entire atmosphere.

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    Modified: 12/09/1995 by goddyn@sfu.ca (Luis Goddyn)