text: the proportion of the ambient air temperature 
  and the standard sea level air temperature. 
  This temperature ratio is assigned the short- 
  hand notation of 0 (theta). 
  Temperature ratio 
  
  percent water vapor, argon, carbon dioxide, 
  etc. For the majority of all aerodynamic con- 
  is considered as a uniform 
  siderations air 
  mixture of these gases. The usual quantities 
  used to define the properties of an air mass are 
  as follows: 
  
  Ambient air temperature 
  =Standard sea level air temperature 
  
  STATIC PRESSURE. The absolute static 
  pressure of the air is a property of primary 
  importance. The static pressure of the air 
  at any altitude results from the mass of air 
  supported above that level. At standard sea 
  level conditions the static pressure of the air 
  is 2,116 psf (or 14.7 psi, 29.92 in. Hg, etc.) 
  and at 40,000 feet altitude this static pressure 
  decreases to approximately 19 percent of the 
  sea level value. The shorthand notation for 
  the ambient static pressure is “p” 
  and the 
  standard sea level static pressure is given the 
  subscript “a” 
  for zero altitude, pa. A more 
  usual reference in aerodynamics and perform- 
  ance is the proportion of the ambient sta~tic 
  pressure and the standard sea level static 
  pressure. This static pressure ratio is assigned 
  the shorthand notation of 8 (delta). 
  
  @=TITtl 
  ,+273 
  
  288 
  
  Many items of compressibility effects and jet 
  engine performance involve consideration of 
  the temperature ratio. 