temperature inversion
A temperature inversion is an atmospheric condition in which air temperature increases rather than decreases with altitude. It matters in the investigation of UFO phenomena because it changes how light and radar waves propagate.
A temperature inversion is an atmospheric condition in which, within a certain layer, air temperature increases rather than decreases with altitude. Normally the air cools with altitude, but during an inversion a warmer layer of air sits above colder air. It often forms on clear, calm nights when the ground cools quickly, but it can also occur with large, subsiding air masses.
Why does it matter for UFO phenomena?
At the boundary of the inversion layer, the density of the air, and with it its refractive index, changes abruptly, so light and radio waves propagate along a bent path rather than in a straight line. This is one form of refraction. For radio waves, an abrupt change in humidity also plays an important role. Possible consequences:
- distortion, color change or apparent displacement of distant light sources (stars, planets, car headlights, the lights of towns), as well as amplification of the twinkling caused by atmospheric turbulence;
- the appearance of objects below the horizon, mirage-like images (fata morgana);
- the bending of radar waves, which can cause "anomalous reflections" from objects on the ground, meaning that returns can appear on the radar screen with no real flying object behind them.
Official and skeptical position
According to official investigations and skeptics, temperature inversion is a common explanation for UFO reports and radar detections that seem inexplicable at first glance. In July 1952, for example, the Air Force used it to explain the Washington radar sightings. However, this explanation was disputed even at the time, including by Edward J. Ruppelt, who headed the Air Force's UFO program. According to some ufologists, an inversion does not explain every detail, so assessments of individual cases differ.