AEROGRAPHER'S MATE 3 & 2 



in going from Fahrenheit to Celsius, use the 

 smaller ratio. 



Another method of converting tempsratures 

 from one scale to another is the decimal 

 method. This method uses the ratio 1° C 

 equals 1.8° F. To find Fahrenheit from Celsius, 

 multiply the Celsius value by 1.8 and add 32. 

 To find Celsius from Fahrenheit, subtract 32 

 from the Fahrenheit and divide the remainder 

 by 1.8. 



A third method of temperature conversion 

 is based on the fact that the Fahrenheit and 

 Celsius scales both register the same tempera- 

 ture at -40°; that is, -40° F equals -40° C. 

 This method of conversion, sometimes called 

 the "40 rules," proceeds as follows: 



1. Add 40 to the temperature which is to 

 be converted. Do this whether the given 

 temperature is Fahrenheit or Celsius. 



2. Multiply by 9/5 when changing Celsius 

 to Fahrenheit; by 5/9 when changing Fahrenheit 

 to Celsius. 



3. Subtract 40 from the result of step 2. 

 This is the answer. 



Remember that the multiplying ratio for 

 converting F to C is 5/9, rather than 9/5. 

 Also remember to always ADD 40 first, then 

 multiply, then SUBTRACT 40, regardless of 

 the direction of the conversion. 



To change a Celsius reading to an absolute 

 value, add the Celsius reading to 273° 

 algebraically. For example, minus 35° C is 

 equivalent to 238° absolute, arrived at by adding 

 minus 35° C to 273°. 



To change a Fahrenheit reading to an 

 absolute value, first convert the Fahrenheit 

 reading to its equivalent Celsius value, which 

 is then added algebraically to 273°. Consequently, 

 50° F is equivalent to 283° absolute, arrived at 

 by converting 50° F to 10° C and then adding 

 the Celsius value algebraically to 273°. 



VERTICAL DISTRIBUTION 



The earth's atmosphere is divided into 

 layers or zones according to various dis- 

 tinguishing features, as illustrated in figure 

 12-7. The temperatures shown here are generally 

 based on the latest "U.S. Extension to the ICAO 

 Standard Atmosphere" and are representative 

 of mid-latitude conditions. The extension shown 



in the insert is speculative. These divisions are 

 for reference of thermal structure (Lapse 

 Rates) or other significant features and are 

 not intended to imply that these layers or zones 

 are independent domains. The earth is surrounded 

 by one atmosphere, not by a number of sub- 

 atmospheres. 



Terms 



In discussing vertical distribution of the 

 earth's atmosphere, several terms are used 

 that should be understood by the Aerographer. 



LAPSE RATE. — In general, lapse rate is 

 the rate of decrease in the value of any 

 meteorological element with elevation. However, 

 it is usually restricted to the rate of decrease 

 of temperature with elevation; thus, the lapse 

 rate of the temperature is synonymous with 

 the vertical temperature gradient. The tempera- 

 ture lapse rate is usually positive, which means 

 that the temperature decreases with elevation. 



INVERSION. — Inversions describe the atmos- 

 pheric conditions when the temperature increases 

 with altitude, rather than decreases as is usual. 

 Inversions result from the selective absorption 

 of the earth's radiation by the water vapor in 

 the air, and also from the sinking or subsidence 

 of air, which results in its compression and, 

 therefore, heating. Either effect alone may 

 cause an inversion; combined, the inversion 

 would be stronger. 



Inversions are a frequent occurrence, 

 especially at night, in the Tropics, and in the 

 Polar regions. For night conditions all over 

 the world, for the polar regions, and for the 

 tropical regions, it may be said that inversions 

 in the lower levels are the rule rather than 

 the exception. 



ISOTHEaMAL, — In the isothermal lapse rate, 

 no cooling or warming is noted, and the rate 

 is zero with height. 



The_e three general temperature changes 

 through a given layer of air with height, should 

 not be confused with the rate of cooling of an 

 air parcel ascending through a layer, which 

 will be discussed in the adiabatic processes 

 later in this chapter. 



264 



