Definition
An atmospheric condition in which a radar or radio beam bends less than it would under standard atmospheric refraction, causing the beam to travel in a path closer to a straight line and dip below the normal coverage area. This reduces the effective range at which targets near or below the horizon can be detected.
Plain English
A weather condition that makes radar and radio signals bend downward less than usual, so they reach less far around the curve of the earth and can miss low targets that would normally be picked up.
Context Anchor
Seen in discussions of radar coverage, radio reception, and how weather conditions affect signal travel.
Derivation
From the Latin 'sub' meaning 'under' or 'less than,' combined with 'refraction,' the bending of a wave as it passes through different mediums. So 'subrefraction' literally means 'less bending than expected' — bending below the standard amount.
Why Pilots Care
Can shorten effective radar and radio ranges, reducing detection or communication distance below expected values.
Grounding Statement
Picture a radar beam that normally curves gently downward to follow the earth's surface — under subrefraction, the beam stays straighter and shoots out into space sooner, leaving a gap close to the ground.
Intuition Check
Subrefraction does not mean the signal stops bending completely. It means the signal bends less than normal.
Example Sentence 1
Subrefraction conditions that morning shortened the radar's effective range, and controllers lost low-level returns earlier than usual.
Example Sentence 2
Subrefraction reduced VHF range, so the pilot switched to a higher altitude for better contact.