One of the “hot” areas of atmospheric research these days is in the study of the phenomena of ice supersaturation. Ice supersaturation is when the relative humidity with respect to ice in the atmosphere exceeds 100%. Under these conditions, the sky is clear with no clouds.
Cirrus clouds in the upper troposphere have only a loose relation to ice saturation. They do not typically form at saturation and once formed they are not very strongly attracted by the equilibrium state. Thus, there is plenty of ice supersaturated, yet clear air in the upper troposphere.
Google the term ice supersaturation and you will find hundreds of research papers by scientists from all over the globe studying this phenomena.
Here is an interesting abstract of a research paper on contrail formation
This study examines how jet aircraft contrails develop precipitation trails, using data collected on 12 May, 1996 during SUCCESS. The DC-8 sampled the precontrail conditions, produced a contrail largely in clear air at -52°C, and sampled the contrail and developing trails for over an hour. The environment was highly ice-supersaturated, reaching nearly water saturation in some locations. Inside the contrail core, almost all ice particles remained small (∼ 1 to 10 μm) due to high crystal concentrations (∼ 101 to 102 cm-3) which reduced the vapor density to saturation. Mixing of moist environmental air and vapor-depleted contrail air produced localized regions of supersaturation along the contrail periphery, where crystals grew to several hundred microns at about 0.1 μm s-1. These particles could then fall from the contrail into the vapor-rich, undepleted, supersaturated environment below. As heavier crystals left the contrail, others moved into the regions of ice supersaturation. Precipitation trails developed as this process continued over time.
Abstract. During the European heat wave summer 2003
with predominant high pressure conditions we performed a
detailed study of upper tropospheric humidity and ice particles
which yielded striking results concerning the occurrence
of ice supersaturated regions (ISSR), cirrus, and contrails.
Our study is based on lidar observations and meteorological
data obtained at Lindenberg/Germany (52.2_ N, 14.1_ E)
as well as the analysis of the European centre for medium
range weather forecast (ECMWF). Cirrus clouds were detected
in 55% of the lidar profiles and a large fraction of
them were subvisible (optical depth <0.03). Thin ice clouds
were particularly ubiquitous in high pressure systems. The
radiosonde data showed that the upper troposphere was very
often supersaturated with respect to ice. Relating the radiosonde
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. The ECMWF cloud
parametrisation reproduces the observed cirrus clouds consistently
and a close correlation between the ice water path in
the model and the measured optical depth of cirrus is demonstrated.
Does that help your understanding of the issues at all?
We are not talking about cloud seeding, we are talking about contrails.
Contrails form due to combustion exhaust.
Liquid CO2 can not form in combustion exhaust, nor can it form from human exhalations as you claimed.
No, I am talking about Chemtrails. You, are protecting you beloved government. Pathetic fool.
Fortunately the coldest cirrus have the highest ice supersaturation due to the dominance of homogeneous freezing nucleation. Seeding such cirrus with very efficient heterogeneous ice nuclei should produce larger ice crystals due to vapor competition effects, thus increasing OLR and surface cooling. Preliminary estimates of this global net cloud forcing are more negative than –2.8 W m–2 and could neutralize the radiative forcing due to a CO2 doubling (3.7 W m–2). A potential delivery mechanism for the seeding material is already in place: the airline industry.
The Effects of Aircraft Wake Dynamics on Contrail Development
Results of large-eddy simulations of the development of young persistent ice contrails are presented, concentrating on the interactions between the aircraft wake dynamics and the ice cloud evolution over ages from a few seconds to 30 min. The 3D unsteady evolution of the dispersing engine exhausts, trailing vortex pair interaction and breakup, and subsequent Brunt–Väisälä oscillations of the older wake plume are modeled in detail in high-resolution simulations, coupled with a bulk microphysics model for the contrail ice development. The simulations confirm that the early wake dynamics can have a strong influence on the properties of persistent contrails even at late times. The vortex dynamics are the primary determinant of the vertical extent of the contrail (until precipitation becomes significant); and this together with the local wind shear largely determines the horizontal extent. The ice density, ice crystal number density, and a conserved exhaust tracer all develop and disperse in different fashions from each other. The total ice crystal number can be significantly reduced due to adiabatic compression resulting from the downward motion of the vortex system, even for ambient conditions that are substantially supersaturated with respect to ice. The fraction of the initial ice crystals surviving, their spatial distribution, and the ice mass distribution are all sensitive to the aircraft type, ambient humidity, assumed initial ice crystal number, and ambient turbulence conditions. There is a significant range of conditions for which a smaller transport such as a B737 produces as significant a persistent contrail as a larger transport such as a B747, even though the latter consumes almost five times as much fuel. The difficulties involved in trying to minimize persistent contrail production are discussed.
This seeding modified the mid and low level temperature profiles, glaciated the low level clouds, and produced light snow for several hours in the foothills and northwest piedmont. Snowfall amounts were not large in RAH's CWFA, ranging from ½ to 1 inch in the northwest piedmont, and were overshadowed by the larger scale icing event which evolved shortly thereafter. It is clear, however, that the seeder-feeder mechanism alone could easily produce an "advisory-scale" event, consisting of either frozen or freezing precipitation.
The feeder-seeder mechanism can be diagnosed by carefully examining the entire depth of the soundings. Very small changes in the vertical temperature profile can profoundly affect the p-type, and models often cannot resolve these details