top of page


Atmospheric Stability

When the temperature decreases with an increase in altitude it is called the lapse rate.

As the air ascends (lowers) through the atmosphere, the rate of temperature changes 2° C per 1,000 feet.

Water vapor is lighter than air, moisture decreases air density, causing it to rise. Since moist air cools at a slower rate, it is generally less stable than dry air. The dry adiabatic lapse rate (unsaturated air) is 3°C per 1,000 feet. The moist adiabatic lapse rate varies from 1.1°C to 2.8°C per 1,000 feet.

If the atmosphere is in a stable state vertical movement is very little or not at all. However, if the atmosphere is unstable, vertical movement increases becoming turbulent. In this lesson, we will cover:

  • Moisture and Temperature

  • Inversion

  • Relative Humidity

  • Temperature/Dew Point

Moisture and Temp.:

The amount of moisture present in the atmosphere is dependent upon the temperature of the air. Water is present in the atmosphere in three states: liquid, solid, and gaseous. All three forms can readily change to another, and all are present within the temperature ranges of the atmosphere.

These changes occur through the processes of evaporation, sublimation, condensation, deposition, melting, or freezing. However, water vapor is added into the atmosphere only by the processes of evaporation and sublimation.

Sublimation is the process when a solid material such as ice, changes directly into a vapor by skipping the liquid stage. An example of sublimation is Dry ice.

Temperature Inversion:

An inversion is when the temperature of the air increases with altitude. Surface based inversions can occur on clear cool nights when the air close to the ground is cooled. The air on the surface becomes cooler than the air a few hundred feet above it.

For example, a current of warm air aloft overrunning cold air near the surface produces an inversion aloft.

Relative Humidity:

Humidity is the amount of water vapor in the atmosphere at a curtain time. Whereas relative humidity is the actual amount of moisture in the air compared to total amount of moisture the air holds at a curtain temperature.

An example of this is if the relative humidity is at 65%. Therefore, it means the air can only hold 65% of the moisture at a curtain temperature.

Temperature/Dew Point:

Dew point, which is given in degrees of Celsius, is the temperature the air can no longer hold any more moisture.

When the temperature and the dew point are the same, the air has become completely saturated with moisture. This means that clouds, dew, fog, rain, snow, etc. is present.


Leave your comments below


bottom of page