|
The U.S. Standard Atmosphere is an atmospheric model of how the pressure, temperature, density, and viscosity of the Earth's atmosphere change over a wide range of altitudes or elevations. The model, based on an existing international standard, was first published in 1958 by the U.S. Committee on Extension to the Standard Atmosphere, and was updated in 1962, 1966, and 1976. It is largely consistent in methodology with the International Standard Atmosphere, differing mainly in the assumed temperature distribution at higher altitudes. ==Methodology== The USSA mathematical model divides the atmosphere into layers with linear temperature distributions against geopotential altitude. The other two values (pressure and density) are computed by simultaneously solving the equations resulting from: * the vertical pressure variation (which relates pressure, density and geopotential altitude), using a standard pressure of at mean sea level as a boundary condition, and * the ideal gas law (which relates pressure, density, and temperature), at each geopotential altitude. Air density must be calculated in order to solve for the pressure, and is used in calculating dynamic pressure for moving vehicles. Dynamic viscosity is an empirical function of temperature, and kinematic viscosity is calculated by dividing dynamic viscosity by the density. Thus the standard consists of a tabulation of values at various altitudes, plus some formulas by which those values were derived. To allow modeling conditions below mean sea level, the troposphere is actually extended to , where the temperature is , pressure is , and density is . 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「U.S. Standard Atmosphere」の詳細全文を読む スポンサード リンク
|