Definition
A thermodynamic process in which a parcel of unsaturated air changes temperature solely because it is compressed or expanded, with no heat added to or removed from the parcel and no condensation of water vapor occurring. As the parcel rises, it expands and cools at the dry adiabatic lapse rate of approximately 3 degrees Celsius (5.4 degrees Fahrenheit) per 1,000 feet. As it descends, it compresses and warms at the same rate.
Plain English
When a pocket of dry air rises, it expands and gets cooler. When it sinks, it gets squeezed and warms up. The temperature change comes only from the change in pressure, not from heat moving in or out. As long as no clouds are forming in the air, this happens at a steady rate of about 3 degrees Celsius for every 1,000 feet of altitude change.
Context Anchor
Seen in aviation weather discussions about rising air, sinking air, cloud formation, and how stable or unstable the air may be.
Derivation
Dry means the air is unsaturated, so no water is condensing. Adiabatic comes from the Greek adiabatos, meaning 'not to be passed through' -- the idea being that no heat passes through the boundary of the air parcel. So 'dry adiabatic' literally means: temperature change in unsaturated air, with no heat crossing in or out.
Why Pilots Care
This process determines how temperature and atmospheric stability change with height, directly affecting turbulence, cloud development, and visibility along a flight path.
Grounding Statement
Imagine pumping up a bicycle tire -- the pump gets warm because the air inside is being compressed. The same thing happens to sinking air in the atmosphere. Rising air does the opposite: it expands and cools, like air rushing out of that same tire feeling cool on your hand.
Intuition Check
Dry does not mean “no water vapor.” Here it means the air is not saturated. Adiabatic does not mean “no temperature change.” It means any temperature change comes from expansion or compression, not from heat flowing in or out.
Example Sentence 1
As the unsaturated air parcel rose over the mountain, it cooled at the dry adiabatic rate of 3 degrees Celsius per 1,000 feet.
Example Sentence 2
Forecasters apply the dry adiabatic process to predict the height of the freezing level when no moisture is condensing.