Definition 1 of 2
Definition
Long-wavelength infrared energy radiated from the surface of the earth back into the atmosphere, primarily after the surface has been warmed by solar radiation during the day. Terrestrial radiation is the main mechanism by which the earth loses heat, and is a major driver of nighttime cooling, surface temperature inversions, radiation fog, and frost.
Plain English
Heat that the ground gives off back into the air, especially at night after the sun has gone down. The ground soaked up heat from the sun during the day; now it's releasing that heat upward, which cools the surface and the air just above it.
Context Anchor
Seen in aviation weather discussions about nighttime cooling, fog formation, low clouds, and temperature changes near the ground.
Derivation
From Latin terrestris, meaning 'of the earth or land.' So 'terrestrial radiation' literally means radiation coming from the earth itself — as opposed to solar radiation, which comes from the sun.
Why Pilots Care
Helps predict rapid surface cooling that forms radiation fog and affects visibility and temperature forecasts.
Analogy
Think of asphalt on a summer evening. Long after the sun has set, you can still feel heat radiating up off the pavement. That's terrestrial radiation — the ground returning the heat it absorbed during the day.
Grounding Statement
On a clear, calm night, the ground radiates its stored heat upward into space, cooling itself and the air just above it — which is why the coolest air is often right at the surface by dawn.
Intuition Check
Terrestrial radiation does not mean dangerous nuclear radiation. Here, it means ordinary heat energy released by the Earth’s surface.
Example Sentence 1
After a clear, calm night, terrestrial radiation cooled the surface enough to form a thin layer of radiation fog over the runway.
Example Sentence 2
The forecast mentioned strong terrestrial radiation so we expected early morning visibility restrictions.