| kind | characteristics | conditions | best seen from … |
|---|---|---|---|
| inferior-mirage flash | Joule's “last glimpse”; oval, flattened below; lasts 1 or 2 seconds | surface warmer than the overlying air | close to sea level |
| mock-mirage flash | indentations seem to “pinch off” a thin, pointy strip from the upper limb of the Sun; duration 1 or 2 sec. | atmospheric inversion layer below eye level; surface colder than air | the higher the eye, the more likely; flash is most obvious when the eye is just above the inversion |
| sub-duct flash | large upper part of an hourglass-shaped Sun turns green for up to 15 sec. | observer below a strong atmospheric inversion | in a narrow height interval just below a duct (can occur at any height) |
| green ray | green beam of light that seems to shoot up from a green flash, or is seen immediately after sundown. Usually only a few degrees long; lasts no longer than a couple of seconds | hazy air and a bright green flash of one of the kinds named above that acts as a light source | ?? |
Remarks: Most (about 2/3 or 3/4) of all observations involve inferior-mirage flashes. The rest are for the most part mock-mirage flashes. The two other kinds are rare and constitute only about 1 per cent of all reports. Not all kinds are named here — there are also some that are not understood, such as the cloud-top flash (which usually is seen as the Sun sinks into the coastal fog, but sometimes also at distant cumulus clouds). And Alistair Fraser's flashes, which are seen in hilly country, and are a variant of the mock-mirage flash in places where inversions are pushed up over hills.
(An earlier version of this sidebar accompanied my Zenit article.)
© 1999, 2000, 2005, 2006, 2012 Andrew T. Young