Atmospheric Stability
The stability of air is determined by comparing the temperature of a rising parcel of air to that of its surroundings. Stable air is able to resist upward movement. For example, if the rising air is colder than its environment it will be more dense (heavier) and sink back to its original level. However, if the rising air is warmer than its environment it will be less dense (lighter) than its surroundings and will continue to rise until it reaches the same temperature as its environment. This is unstable air.
We will now refer to the lapse rate, the rate at which temperature changes with altitude, as the environmental lapse rate. This is because this is the rate at which the temperature of the air surrounding us will be changing if we climbing up into the atmosphere.
