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2.3.1: Hypotheses

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    78094
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    Hypothesis 2.1 (Standard atmosphere)

    The basic typotheses of ISA are:

    • Complies with the perfect gas equation:
      \[p = \rho RT, \label{eq2.3.1.1}\]
      where \(R\) is the perfect gas constant for air (\(R = 287.053 [J/kg\ K]\)), \(p\) is the pressure, \(\rho\) is the density, and \(T\) the temperature.
    • In the troposphere the temperature gradient is constant.
      \[\begin{array} {c} {\text{Troposphere } (0 \le h < 11000 [m])} \\ {T = T_0 - \alpha h,} \end{array}\]
      where \(T_0 = 288.15 [K], \alpha = 6.5 [K/km]\).
    • In the tropopause and the inferior stratosphere the temperature is constant.
      \[\begin{array} {c} {\text{Tropopause and inferior stratosphere } (11000 [m] \le h < 20000 [m])} \\ {T = T_{11}} \end{array}\]
      where \(T_{11} = 216.65[K]\).
    • The air pressure at sea level (\(h = 0\)) is \(p_0 = 101325 [Pa]\). In Equation (\(\ref{eq2.3.1.1}\)), the air density at sea level yields \(\rho_0 = 1.225 [kg/m^3]\).
    • The acceleration due to gravity is constant (\(g = 9.80665 [m/s^2]\)).
    • The atmosphere is in calm with respect to Earth.

    2.3.1: Hypotheses is shared under a CC BY-SA 3.0 license and was authored, remixed, and/or curated by Manuel Soler Arnedo via source content that was edited to conform to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.

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