Persistent Contrail

I wanted to know the difference between contrail ( fades with 5 seconds to 2 minutes ) and persistent contrails ( can be in the sky for many hours. Up to 14 hours )
In order for a contrail to spread and become a persistent contrail the air surounding the contrail must be supersaturated with regards to ice.
So I wanted to know: What is saturated and what is supersaturated.
Saturated with regards to ice is the frost point. So I used the Vaisala humidity calculator to calculated the frost point aka saturated air with regards to ice.
It also depends on temperature.
Here are the results:
Frost point aka saturated with regards to ice. Add 10% to the figures to get  the formation of ice particles by heterogeneous
Take figures and divide by 10 and multiply with 11. See here #01 01
Frost Point:

contrail-cirrus supersaturated ice
<backup here: acp-8-1689-2008>
radiosonde data showed that the upper troposphere was very
often supersaturated with respect to ice. Relating the ra-
diosonde profiles to concurrent lidar observations reveals that
the ISSRs almost always contained ice particles. Persistent
contrails observed with a camera were frequently embedded
in these thin or subvisible cirrus clouds.
<backup here: WN3E_Session_special_Burkhardt>
In ice supersaturated air
contrails are persistent
weakly ice supersaturated -
only ice in secondary wake
is persistent
strongly ice supersaturated
- ice in primary and
secondary wake persistent
Contrail cirrus evolve in supersaturated area
<backup here: Schumann_Contrails>
Condensation trails (c
ontrails) are aircraft induced cirrus clouds, which may persist and
grow to large cirrus cover in ice-supersaturated air, and may cause a warming of the atmosphere.

Contrails persist if the ambient humidity is larger than saturation humidity over ice surfaces (relative humidity over ice
RHi larger than 100 %). <how much larger than 100%>
In such ice-supersaturated air masses, the ice particles
within the contrails grow by deposition of water vapour molecules from the ambient air. Contrails may
persist as long as the ambient air in which the contrail forms stays ice-supersaturated [

Contrails form and persist also in weakly ice-supersaturated air.  < how much is weakly ice-supersaturated? More than 100% anyway>
However, the formation of cirrus
requires higher relative humidity than for contrail persistence: Ice particles form from the abundant
small droplets by homogeneous freezing only at high relative humidity with respect to ice-saturation,
at RHi of the order 145 to 165 % or higher

See here #02 02
 [39]. Also the formation of ice particles by heterogeneous
nucleation often requires
RHi of 110 % or more
I guess this anwers my questions.
Since I never saw a "persistent-contrail" in my life the first 50 years of my life my guess is that that time we had only homogeneous freezing only at RHi of 145% to 165% or higher.
At -40 Celsius 148.3 RHi is the same as 100% RH with regards to water. 145% RHi would be about 98% RH with regards to water. No wonder I never saw a "persistent-contrail" in Europe prior to 9/11 in 2001.
Now lets look at the heterogeneous nucleation of 110% RHi or more. I think this is related to cloud seeding and silver iodide.
110% RHi is 10% than the frost point in the yellow table higher up. Will add a new table for this in a day or two.

(with few exceptions such as desert dust particles). Often,
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
3.4.1. Cirrus and Contrails
 For instance, supersaturations in excess of 40-50% with respect to ice are needed for sulfuric acid particles to freeze homogeneously
supersaturations in excess of 40-50% with respect to ice =
140-150% RHi
Use the figures in the table on the left and add 2- 5- or 10% for RH values with regards to water.

(Tabazadeh et al., 1997) at temperatures above 200 K. Observations of relative humidity with respect to ice at the leading edges of wave clouds are consistent with the requirement of large ice supersaturations for nucleation of ice on the bulk of the atmospheric aerosol (Heymsfield et al., 1998a; Jensen et al., 1998c). Hence, there is a large supersaturation range in which heterogeneous nuclei could lead to cirrus formation before the bulk of the atmospheric particles freeze (DeMott et al., 1997). This potential for heterogeneous nuclei to cause ice formation at ice supersaturations that are relatively low compared to those needed to freeze sulfate particles leads to concern about the role of aircraft exhaust in modifying ambient clouds (Jensen and Toon, 1997).
Contrails spread and persist in ice supersaturated air masses. Contrails are visible also for several minutes or even longer when the relative humidity is slightly below saturation, in particular at low temperatures.
The life-time of contrail clusters should be similar to the lifetime of ice supersaturated regions
<backup here: Schiller-3>
Homogeneous / heterogeneous ice nucleation
homogeneous ice nucleation 140-170%  RHi (ice)
heterogeneous ice nucleation 100-150% RHi (ice)
<100% RHi = see yellow table higher up>
<backup here: 169-216>
in the wake of the air-
craft. If the surrounding air is ice-supersaturated these contrails
become persistent
and transform
into cirrus clouds and can pers
ist for several hours (IPCC,1999)
This implies that in a substantial fraction of the upper
troposphere, contrail cirrus can persist in supersaturated air that is
Of the flight distance, only
a fraction (given by the supersaturated area fraction) results in persistent contrails.
CCMod simulates the life cycle of those persistent contrails. Contrails are advected
by the wind field and remain in (and are limited by) the ice-supersaturated
fraction of a grid box, assuming that persistent contrail cirrus predominantly
form in large persistent ice-supersaturated areas, such as prefrontal areas, in
which they remain for a long time.
<backup here: fusina_etal07>
By constructing an
idealized profile from the measurement data the radiative properties of ISSRs and thin
cirrus containing ice supersaturation were studied. The impact of ISSRs on the surface
forcing is negligible but locally, within the vertical profile, changes in the heating rates up
to 1 K d1
for typical values of 130% relative humidity with respect to ice compared to the
saturated profiles are found. This is also important for the local dynamics within the
supersaturated layers
or homogeneous nucleation,
 which is prob
ably the dominant mechanism for forming ice crystals at low temperatures
T<38C) relative humidities in the range 140–170% RHi, depending on temperature
<see my above Turquoise table>
[Koop etal., 2000], are required. For heterogeneous nucleation, the
freezing thresholds are smaller, probably in the range 110–140%RHi
< see my yellow table and add 10% to those figures or more. Divide figures by 10 and multiply with 11 >
 [e.g.,Mohler et al., 2006;DeMott et al., 2003].
[3] The properties and global distributions of ice super-
saturated regions (ISSRs) were discovered during the last
years [e.g.,Gierens et al., 1999, 2000;Spichtinger et al.
,2003a, 2003b;Gettelman et al., 2006].
<backup here: Global Modeling of Contrail>
Contrails form and persist in air that is
ice saturated, whereas natural cirrus usually requires
high ice supersaturation to form (Jensen et al. 2001).
This difference implies that in a substantial fraction
of the upper troposphere contrail cirrus can persist
in supersaturated air that is cloud free,
110% RHi or more. I will now calculate 110% RHi
Click here to go one level up or here for the index page.

It's a jpg pictures. Download it.
Adding further data with sources. You can download the pdf files from here......
If you don't want to download the pdf file from my site, copy paste the name and add pdf and search in google with the name.
supersaturation mentioned:
Ice supersaturations exceeding 100% at
the cold tropical tropopause: implications
for cirrus formation and dehydration
Recent in situ measurements at tropical tropopause temperatures as low as 187 K indicate
supersaturations with respect to ice exceeding 100% with little or no ice present.
In contrast, models used to simulate cloud formation near the tropopause assume a
5 supersaturation threshold for ice nucleation of about 65% based on laboratory measurements
of sulfate aerosol freezing.
Previous in situ measurements of ice satu15
rations ratios ranging from 1.1–1.7 (i.e. supersaturations of 10–70%)
The ice saturation ratio
15 (si ) at the tropopause indicated by the water vapor and temperature measurements
is about 2.3–2.4 (i.e. about 130–140% supersaturation with respect to ice).
Atmos. Chem. Phys. Discuss., 4, 7433–7462, 2004
SRef-ID: 1680-7375/acpd/2004-4-7433
İ European Geosciences Union 2004
Previous studies of in-cloud and clear sky water vapour
measurements in the upper troposphere reveal high supersaturations with respect to ice
occasionally exceeding even water saturation.
1.2.2 Supersaturation inside and outside of cirrus clouds
In the complete
absence of aerosols, cloud droplets could not form without supersaturations of several
hundred percent.
Consequently aerosols largely affect the initial cloud droplet number
concentration, cloud lifetime and albedo (Giannakaki et al., 2009).
As described by IPCC (2007), uncertainties about the aerosol effects for mineral dust
are particularly high.
The solid curve where all solutions freeze is the freezing temperature threshold. For
example, at temperatures lower than 233 K (-40◦C) this process requires airmasses in a
state of substantial supersaturation which is generally larger than 40% (Spichtinger et al.,
presented by
Dipl. Geogr., University of Zurich
born 16 March 1978
citizen of Switzerland
accepted on the recommendation of
Prof. Dr. T. Peter, examiner
Dr. F. G. Wienhold, co-examiner
Dr. H. V¨omel, co-examiner
At saturation,
the relative humidity (RH) is defined to be 100%. An RH value
greater than this corresponds to supersaturation. Saturating
water vapour pressure over ice is less than that over water, and
therefore supersaturation with respect to ice is attained earlier
than with respect to water.
The formation of cirrus clouds in environments with moderate
to strong upward draughts or few germs is dominated
by homogeneous nucleation, as elaborated by Tompkins et al.
[5]. The relative humidity with respect to ice increases up to a
critical threshold RHcrit of supersaturation as high as 150%,
before nucleation begins under conditions of low temperature
and large difference between the vapour pressures of liquid
water and ice saturation.
P. Mahapatra, M. Milz and S. Buehler
Satellite Atmospheric Science Group, Department of Space Science, Luleċ University of Technology, Kiruna, Sweden
\tracking\Heymsfield et al GRL 1998.pdf
Earlier findings are supported that RH,• in
mid-latitude, continental environments decreases from
water-saturation at temperatures above-39ĝC to 75%
RH at-55ĝC.  <table>
data indicate that RH•,,c below-55ĝC is between 70
and 88%. RH,•,c may also dependo n characteristics of
the aerosol
Andrew J. Heymsfield, Larry M. Miloshevich, and Cynthia Twohy
National Center for Atmospheric Research, Boulder, CO
Glen Sachse
NASA Langley Research Center, Hampton, VA
Samuel Oltmans
NOAA Climate Monitoring and Diagnostics Laboratory, Boulder, CO
Liquid droplets to ice crystals
- not difficult if T < -40°C, relative humidity (RH) > 100% <see table>
- all droplets freeze instantaneously if T < -40°C

Patrick Minnis
NASA Langley Research Center
Hampton VA, USA
Aircraft measurements made in cirrus during FIRE II show highly ice-supersaturated
regions in clear air, placing a lower bound on the RH required for cirrus formation
approximately equal to (RHlm-10)%.
Space Vehicles Directorate
29 Randolph Rd.
-40C = 100% RH with respect to water. 148.3% with respect to ice
After a short (about 1 s)
initial growth stage (Ka¨rcher et al. 1996), the contrail
will evaporate within tens of seconds if the air is dry.
In contrast, contrail growth will continue in background
air that is supersaturated with respect to ice
. Eventually,
the line-shaped contrail may transform into a cirrus
cloud, as demonstrated by satellite observations (Schumann
andWendling 1990; Minnis et al. 1998; Mannstein
et al. 1999). T
* Institut fu¨r Physik der Atmospha¨re, DLR, Oberpfaffenhofen, Germany
1 Laboratoire de Meteorologie Physique, Universite´ Blaise Pascal, Clermont-Ferrand, France
# Meteorologiska Institutionen, Stockholms Universitet, Stockholm, Sweden
& Institut fu¨r Stratospha¨renchemie, ICG-1, Forschungszentrum Julich, Germany
(Manuscript received 9 September 1998, in final form 2 March 1999)

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