PREPARATION OF CHARTS Boz 2 
temperature 20.4° 
raob temperature at 500 mb. -7.5° 
computed condensation temperature 4.2° 
temperature on pseudo-adiabatic curve at 500 mb -4.8° 
The stability index is then: 
-7.5° - (-4.8°) = -2.7° or -3° to the nearest whole degree and 
entered 
13.2 When not to Compute Stability Index. The stability index will not 
be computed when the relative humidity is missing at the base level, or 
when the temperature is missing or doubtful at the base level or at the 
500 mb. level. 
14, Determination of Tropopause Level for Transmission Purposes. 
The tropopause is defined in terms of temperature lapse rate change, 
pressure level, and thickness of strata as described below. 
14,1 Criteria for Selecting Tropopause Level. 
a. At pressures of 500 mb or less: 
(1) The lowest level, with respect to altitude (at or between 
500 and 30 mbs), at which the temperature lapse rate de- 
creases to 2°C/km or less. 
(2) The average lapse rate from this leveltoany point within 
the next higher two km doesnot exceed 2°C/km. 
(3) The flight must extend at least two km above the tropo- 
pause level. 
b. At pressures greater than500 mb (onlyifno tropopause found 
at pressures of 500 mb or less). 
(1) The highest level, with respect to altitude, at which the 
temperature lapse rate decreases to 2°C/km or less. 
(2) The average lapse rate from this level toany point within 
the next higher two km doesnot exceed 2°C/km. 
1-1-69 FMH#3 
