Angel
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Angel
A radar
echo caused by a physical phenomenon not discernible
to the eye.
Angels are usually
coherent echoes and sometimes
of great signal strength (up to 40 decibels above the noise level).
They have been ascribed to insects flying through the radar beam,
but have also been observed under atmospheric conditions which
indicate there must be other causes. Studies indicate that a fair
portion of them are caused by strong temperature or moisture gradients,
or both, such as might be found near the boundaries of bubbles
of especially warm or moist air (see
blob). They frequently
occur in shallow layers at or near temperature inversions within
the lowest few thousand feet of the atmosphere.
References
This article is based on NASA's Dictionary of Technical Terms for Aerospace Use