Definition
A slow, broad downward movement of air over a large area. As the air sinks, it is compressed by the higher pressure at lower altitudes, which warms it and reduces its relative humidity. Subsidence is associated with high-pressure systems and typically produces clear skies, stable air, and suppressed cloud development.
Plain English
A wide, gentle sinking of air from higher altitudes toward the ground. As the air sinks it warms and dries out, which is why high-pressure areas usually bring fair, settled weather.
Context Anchor
Seen in aviation weather discussions, especially when describing high-pressure systems, stable air, cloud cover, and visibility trends.
Derivation
From the Latin subsidere, meaning 'to sink down' or 'to settle.' The same root gives us 'subside' — as when floodwaters subside. In meteorology it describes air settling downward over a region.
Why Pilots Care
Subsidence produces stable air that can create temperature inversions, trap moisture near the surface, and reduce visibility through fog or haze.
Grounding Statement
Picture a broad area of air slowly pressing downward; as it sinks, it warms, dries, and makes cloud growth harder.
Intuition Check
Subsidence does not mean the ground is sinking here. In aviation weather, it means air is sinking in the atmosphere.
Example Sentence 1
The forecaster mentioned strong subsidence aloft, which explained the clear skies and the haze layer trapped beneath the inversion.
Example Sentence 2
Subsidence inversions can trap smoke and lower visibility, so the pilot delayed departure until the layer mixed out.