Definition
An upward-moving current of air, typically caused by wind striking rising terrain such as a hill, ridge, or mountain slope and being deflected upward.
Plain English
Air that is being pushed upward, usually because wind has run into a slope and had nowhere to go but up.
Context Anchor
Seen in weather and soaring discussions, especially when describing rising air near terrain, waves, or uneven heating of the ground.
Derivation
From 'up' plus 'swell,' meaning to rise or bulge outward. The word pictures air swelling upward against a slope.
Why Pilots Care
Upswells on the windward side of ridges can give a useful lift, but the matching downdraft on the leeward side can be strong enough to exceed an aircraft's climb performance. Recognising one means anticipating the other.
Grounding Statement
Picture a wide sheet of air slowly bowing upward and carrying the airplane with it.
Intuition Check
Do not think of an upswell only as an ocean wave. In aviation weather, it means air rising or bulging upward.
Example Sentence 1
The glider pilot worked the upswell along the windward side of the ridge to gain altitude without using the engine.
Example Sentence 2
The weather report mentioned an upswell over the valley that could affect low-level flight.