The Yellow Table

The Yellow Table aka persistent but not spreading contrails and threshold for cirrus cloud existence. Anything less humid is to dry.
"Persistent-contrails" is BS ( see my opinion about it ) but here it is:

Frost Point:

Contrails persist if the ambient humidity is larger than saturation humidity over ice surfaces (relative humidity over ice
RHi larger than 100 %)
see link ... or www link:
RHi is large enough to let contrails persist and develop into cirrus but not large enough to
let cirrus clouds form naturally. Since contrail persistence requires at least ice saturation, a sky full of
contrails but without natural cirrus shows that cases occur with humidity above ice-saturation but be
-low the threshold for cirrus formation.
Measurements on modern airliners [51] indicated that such aircraft fly in ice-supersaturated air masses about 15 % of the flight time
Water vapour and particles emitted from aircraft engines induce contrails which grow to
larger-scale clouds (
) if the ambient atmosphere is so humid that the humidity exceeds
Since atmospheric regions with ice supersaturation are not very thick (typically 500 m with large
variance) [47], it often would suffice to fly a few hundred meters higher or lower to avoid such regions
Many aspects of contrail formation are well understood. Contrails from for thermodynamic reasons
when the ambient air is cold enough. Persistent contrails form in ice-supersaturated air masses. In such
cases often contrail cirrus forms where no cirrus would form otherwise because ice supersaturation is
often too low for natural cirrus particle nucleation. Airliners fly on average about 15 % of their time in
ice-supersaturated air masses
< from the Schumann_Contrails.pdf >
Back to Index...