Definition
A line on a thermodynamic chart showing how the temperature of a parcel of unsaturated (dry) air changes as it rises or descends, cooling or warming purely due to expansion or compression, with no heat added or removed and no condensation occurring. Dry air following this line cools at approximately 3 degrees Celsius per 1,000 feet as it ascends, and warms at the same rate as it descends.
Plain English
A line on a weather chart that shows how fast a pocket of dry air cools as it rises, or warms as it sinks, just from changing pressure. The standard rate is about 3 degrees Celsius for every 1,000 feet up or down.
Context Anchor
Seen in aviation weather study when comparing rising air, cloud formation, and atmospheric stability.
Derivation
Dry refers to unsaturated air -- air that has not yet reached the point where its moisture condenses into cloud. Adiabat comes from the Greek 'adiabatos,' meaning 'not to be passed through,' referring to a process where no heat passes in or out of the air parcel. The temperature change comes entirely from the air being squeezed or allowed to expand.
Why Pilots Care
Knowing the dry adiabat helps determine atmospheric stability, which affects turbulence, cloud formation, and aircraft performance at different altitudes.
Analogy
Think of a sealed, insulated balloon of dry air floating upward: it cools at a fixed rate simply because it expands, with nothing added or removed.
Grounding Statement
Picture a balloon of dry air pushed upward: as the surrounding pressure drops, the balloon expands and cools at a steady, predictable rate -- that rate is the dry adiabat.
Intuition Check
“Dry” does not mean desert air or air with no water at all. Here it means air that is not saturated, so cloud droplets have not started forming.
Example Sentence 1
The forecaster traced the dry adiabat upward from the surface temperature to estimate the height at which rising air would form clouds.
Example Sentence 2
During the weather briefing the instructor showed how following the dry adiabat from the surface temperature helped predict the height of the cloud base.