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Homework Help: Calculating temperature given altitude

  1. Sep 23, 2012 #1
    1. The problem statement, all variables and given/known data
    I am trying to figure out how to calculate the temperature at any given altitude in the troposphere.

    2. Relevant equations
    Let P=air pressure, V=volume of air above a given altitude, n=number of moles of gas, R=the ideal gas constant, T=temperature, and h=height above sea levelX1 and X2 = the value of X at geographic point 1 and point 2.

    PV=nRT (the ideal gas law)
    Volume of a sphere = 4/3*pi*radius3
    Surface area of a sphere = 4*pi*radius2

    3. The attempt at a solution
    P1/ P2 = V1nRT1 / V2nRT2.

    Now, we don't need to know what n and R are, because they are cancelled out of the equation. So ignore them. We are now left with P1/P2 = V1/V2 * T1/T2.

    V = 4/3*pi*radius of troposphere - (4/3 * pi * (6371.5+h))
    V1 / V2 is pretty obvious and can't be simplified.
    Last edited: Sep 23, 2012
  2. jcsd
  3. Sep 25, 2012 #2
    The main problem that I see with this is that fall off in pressure is governed more by the barometric equation p= p0 exp (–h/A) where A is roughly 7 km, than by an increase in available volume at greater height.

    I do not know how meteorologists do this calculation, but the recommendation of the ICAO Standard atmosphere is that the temperature will fall at a constant rate of 0.0065 °C/m up to 11 km altitude in the temperate zone. Obviously that is an "other things being equal" calculation that cannot take account of local atmospheric conditions.
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