Very much rarer iridescence is that of nacreous or mother-of-pearl clouds. They can glow very brightly and are far higher than ordinary tropospheric clouds. Iridescence is also seen in rocket exhaust trails.

Originally posted by pikypiky
Yes, I am willing to drop the unsubstantiated nonsense behind these normal phenom, called iridescence clouds, if you are willing to believe in the spiritual aspect from a thread, which suggests nacreous clouds as a sign for mankind.

Aircraft flying through such areas during landing
approaches become positively charged in contrast to what is normally
experienced during regular fairweather flights. The explanation is
that if an aluminium fuselage is subject to ventilation of an abnormally
high positive to negative ion ratio, where N+ / N- = 1.3 or more then,
according to Fig. 11, the aircraft must charge positively.

Exhaust charging also plays an important role in geophysical
phenomena such as volcanic eruptions which often produce lightning
and during earthquakes where a glow or earthquake light is emitted
along fissures and cracks

. There is
also a growing interest in planetary atmospheric electricity as a
consequence of data sent back from space probes.

Earthquake light is a rare phenomenon and its existence is still being
questioned by some scientists. It was not before 1965, during the
Matsushiro earthquakes in Japan, that actual photos were obtained of
earthquake light (Yasui, 1968 and 1971). Earthquake light has been
observed as a faint red and white glow for hundreds of miles around
just before the earth begins to shake and crack along a fault zone.
There has been much speculation on what might cause earthquake
light. One fact is certain, that the light must come from atoms that
have been ionized or excited by some mechanism triggered by the earthquake. The light is emitted when a detached or excited electron
falls back again into its stable orbit around the atomic nucleus.
Ionizing collisions in air, between atoms and particles or between
atoms and photons, by far outnumber exciting collisions. Ionization of
air molecules, to the extent where the sky will glow for miles around,
could be caused by corona discharges near the earth's surface or by
ionized exhaust gas escaping from the hot interior below the earth's
crust. It has been suggested that frictional heating of a shear zone will
occur during an earthquake and that the frictional heat will lead to
vaporization of water in and near the shear zone (Lockner et al, 1979).
The result would be a drastic increase in the electric resistivity of the
rock throughout the shear zone coupled with some sort of charge
separation due to the evaporation of water. After enough charge has
been collected in the shear zone, corona discharges along its top edge
would stream into the atmosphere like St. Elmo's fire. One problem,
however, is that corona discharges draw a great deal of current
( 100mA per cm2) and it is difficult to understand how such a current
can be supplied over a highly insulating rock surface. Also, corona is
quite a noisy phenomenon unlike silent earthquake light