Chapter 12 — THE GOVERNING FUNDAMENTALS OF METEOROLOGY 



BALL IN BOWL 



FORCE MOVES BALL 



REMOVED BALL OSCILLATES 



BALL EVENTUALLY 



RETURNS TO ORIGINAL 



POSITION 



(A) ABSOLUTE STABILITY 



A 



BALL BALANCED ON BOWL RELEASE OF FORCE 



PERMITS BALL TO MOVE 



o> 



BALL CONTINUES 

 TO MOVE 



BALL WILL CONTINUE 

 TO MOVE 



(B) ABSOLUTE INSTABILITY 



BALL RESTING ON TABLE 



FORCE MOVES BALL 



FORCE REMOVED, 

 BALL STOPS 



BALL REMAINS IN 

 NEW POSITION 



CO NEUTRAL STABILITY 



209.364 



Figure 12-9. — Analogy depiction of stability. 



pressure, its temperature increases at the rate 

 of 1° C per 100 meters, or 5 1/2° F per 1,000 

 feet. This is known as the dry adiabatic lapse 

 rate. 



Saturation Adiabatic Lapse Rate 



When a mass of air is lifted, it cools at 

 a practically constant rate of 5 1/2° F per 

 1,000 feet as long as it remains unsaturated 

 (relative humidity below 100 percent). If the 

 original moisture is being carried along with 

 the mass as it ascends, it cools to its saturation 

 temperature, and the relative humidity is then 



100 percent. Condensation takes place with any 

 further cooling. For each gram of water con- 

 densed, about 597 calories of heat are liberated. 

 This latent heat of condensation is absorbed by 

 the air, and the adiabatic cooling rate is 

 decreased to 2° to 3° F per 1,000 feet instead 

 of 5 1/2° F per 1,000 feet. The process during 

 the saturated expansion of the air is called 

 the saturation adiabatic, the moist adiabatic, or 

 the pseudoadiabatic process. The pseudoadiabatic 

 process assumes that moisture falls out of the 

 air as soon as it condenses. 



How the temperature of a parcel of air 

 changes in response to these processes can be 



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