This is not a chemtrail! Atmospheric Phenomenen explained

Moreover, it turns out that the initial ice particle concentration and radiative processes are of minor importance in the evolution of contrails, at least during the 30-min simulation period.

Keeping these caveats in mind, the following major results have been obtained from the model simulations described in this paper.

* Long-lived contrails cannot be explained by the amount of water emitted by the aircraft. Although we have not performed a simulation in an atmosphere that is subsaturated with respect to ice, it is quite obvious (in comparing results from runs 3 and 8) that persistent contrails can only form in an atmosphere that is supersaturated with respect to ice.

ams.allenpress.com...(1998)055%3C0796:LESOC%3E2.0.CO%3B2

Long lasting contrails like the ones observed usually occur in parts of the sky that have preexisting patches of cirrus clouds. Since the cirrus clouds are formed of ice crystals like the contrails, cirrus clouds in a region of the sky suggests supersaturation with respect to ice and sufficient heterogeneous nuclei for ice crystals to form (Jenson et al. 1998). The GOES-8 satellite photographs, Figure 3 and Figure 4, taken at approximately at the same time as the contrails were present shows significant cirrus clouds around the Norman area providing a condition necessary for contrail persistence.

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The proposed revisions address two categories of particulate matter: fine particles (PM2.5), which are 2.5 micrometers in diameter and smaller; and inhalable coarse particles (PM10-2.5), which are smaller than 10 micrometers in diameter but larger than PM2.5. EPA has had national air quality standards for fine particles since 1997 and for coarse particles 10 micrometers and smaller (PM10) since 1987

EPA last revised the particulate matter standards in 1997. Under terms of a consent decree, EPA agreed to propose whether to revise the particulate matter standards by December 20, 2005; and committed to finalizing any revisions to the standards by September 27, 2006.

Proposal to Revise the National Ambient Air Quality

Like natural cirrus clouds, contrails can impact
climate through their radiative effects. Persistent
contrails often form in air with relative humidities with
respect to ice (RHI) exceeding 100% but with relative
humidities with respect to water (RH) less than 100%.
Cirrus cloud formation generally requires RH > 100%.
Thus, contrails can form clouds in conditions that would
not support the formation of most natural cirrus. Cirrus
coverage over the USA grew by 0.010/decade between
1971 and 1996, while declining over other land areas
with minimal air traffic 0.017/decade.

The values of RHI at 225 hPa (~12 km) plotted in
Fig. 4 show one supersaturated area over central OH
and Indiana at 1200 UTC and no areas at 1600 UTC.
Over PA, RHI ranges from 90% at the OH border to
50% at the eastern PA border. Over Pittsburgh (PIT)
underneath contrail A at 1200 UTC, the RUC RHI is
80%, while near Aberdeen, MD (ABD), close to C at
1200 UTC, RHI = 55%. A similar value is found over
Dulles, VA (IAD) near contrail D, while RHI = 80% over
Blacksburg, VA (BLK) near the end of E. These values
are too low for sustaining contrails. To determine if
these values are due to the model assimilation process,
the rawinsonde RHI profiles are compared with the
corresponding RUC values at 1200 UTC. in Fig. 5. The
RUC increased RHI at most levels over BLK and PIT
while smoothing or decreasing RHI over ABD and IAD.
No contrails were observed for RHI < 55%.
None of the soundings show RHI > 72%, despite
the fact that the PIT rawinsonde must have passed
through contrail A on its way to the stratosphere. To
support a persistent contrail, the maximum PIT RHI from
the sonde would need to be increased by 35% or more.
Another sounding taken over western OH yielded RHI =
117% at 225 hPa. Natural cirrus clouds were passing
over the Wilmington, OH station at the time. Because it
is theorized that natural cirrus clouds can only form
adiabatically for RHI exceeding 145% or more (Sassen
and Dodd 1989), the dry bias appears to be consistent
in both clear and cloudy skies. To account for the dry
bias, a correction formula was developed by assuming
that most of contrails observed by Sassen (1997; his
Fig. 5b) should have occurred only in supersaturated
conditions. To include most of his contrail observations
above a new line representing RHI = 100%, it is
necessary to specify that RHI = 100% for the sonde
value of RH = 16% at -70°C and RHI = 100% at RH =
72% and -36°C.

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Add to the list of rogues a possible new humanmade factor behind climate change: contrails from high-flying airplanes that spread into larger and longer lasting clouds than researchers had expected. Satellites tracked several contrails over the United States that persisted for up to 17 hours and grew to resemble banks of natural cirrus clouds, according to a report in today's Geophysical Research Letters. If such formations are common, contrails may have a significant impact on climate--especially in areas with heavy traffic overhead.
At high altitudes, particles in jet exhaust become seeds for ice crystals that make up contrails. Ice crystals reflect sunlight during the day, possibly cooling the ground below. They may also trap heat after the sun goes down and make the nights warmer. In the 1960s, scientists proposed that fleets of planes could spawn enough contrails to tweak the climate in industrialized regions. Recent satellite studies over Europe showed that contrails cover about 1% of the sky--seemingly not an important amount. However, those satellites watched only the most obvious contrails: long, narrow streaks, many of which fade quickly. The new research reveals that other contrails can elude detection by mutating into strikingly large, cirruslike clouds.
NASA researchers used geostationary satellites to continuously track three sets of contrails over California and the southern United States in spring 1996. The contrails, floating at altitudes of about 10 kilometers, lasted between 7 and 17 hours and expanded to enormous sizes by catalyzing the growth of a larger cloud with more ice. One cloud reached 35,000 square kilometers--the size of Indiana. At such extents, no satellite or ground-based instrument would recognize the clouds as having arisen from contrails, says atmospheric scientist Patrick Minnis of NASA's Langley Research Center in Hampton, Virginia. If more high clouds that look like natural cirrus are old contrails in disguise, Minnis says, "that could have a strong regional effect on climate." Indeed, other studies point to an increase in cirrus clouds during the last 30 years, possibly due to increases in air traffic.
The contrails' tremendous size surprises atmospheric scientist Brian Toon of the University of Colorado, Boulder. "This may make the number of contrails bigger than we thought, but we don't yet know how to quantify that number," Toon says. He adds that jet exhaust may alter existing cirrus clouds by making them denser or triggering precipitation--another poorly understood link between air travel and climate patterns.

apnet.com/inscight/04151998/grapha.htm
climate.dot.gov...

The RUC model data are representations of the complete 3-dimensional structure of wind, temperature, and humidity over the USA at a resolution of 25 mb and 40 km. The horizontal resolution has been degraded to 1° latitude x 1° longitude to facilitate the computations. Because they are based on a sparse number of actual in situ (balloon sonde) data taken every 12 hours and satellite measurements, the RUC data are not a perfect representation of the various meteorological parameters, especially water vapor. The model humidity at upper levels of the atmosphere is often too low, reflecting the current biases known to exist in our measurement system. Persistent contrails require a relative humidity with respect to ice (RHI) that exceeds 100%. We know that contrails are sometimes observed in areas where estimates of the RHI are less than 100%. The existence of contrails in those locations highlights the "dry-bias" in the humidity fields.

The relative humidity data from the RUC 40km model are suspect since 18 April, 2002. Therefore, all contrail forecasts since April 18, 2002 are suspect.To obtain a better estimate of potential contrail formation, examine the 'Individual level (mb)' results. Select a pressure value between 200 and 250 mb for the best estimate. Relative humidity values above 80% are good indicators of contrails in the new RUC data. You can use any pressure level , but the large values may be too warm for contrail formation.

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The environmental conditions that favor contrail formation and persistence are not well understood primarily due to the limited number of empirical studies. This study presents an empirical model to predict widespread occurrences of contrails (outbreaks), which was developed from a combination of rawinsonde temperature and GOES water vapor information. Environments containing persisting contrails were first identified on Defense Meteorological Satellite Program satellite imagery for the United States for January and April 1987 and then analyzed in more detail using Advanced Very High Resolution Radiometer (AVHRR) satellite digital data. Adjacent clear and cloudy environments not containing contrails were identified to compare with the conditions favorable for contrail persistence. For this purpose, a predictive logistic model was developed through multiple regression analysis.The model performance was evaluated through goodness-of-fit methods and found to be statistically significant across a range of atmospheric conditions. To further evaluate the model and to demonstrate its application on a real-time basis, predictions of the probability of persisting contrails were made for a case day. Comparisons of the predictions to satellite observations of the existing conditions (using AVHRR data) demonstrate good model performance and suggest the utility of this approach for predicting persisting contrail occurrence. Implementation of this model should allow climate researchers to better quantify the influence of contrails on surface climate and natural cloud formation.

adsabs.harvard.edu/abs/1997JApMe..36.1211T

One factor still not completely understood is contrail formation. A condensation trail, or contrail, forms in the wake of an airplane as a result of water vapor and aerosol emissions perturbing the local atmosphere when it is at conditions very close to forming a natural cloud. Although it is apparent that aircraft-emitted particles provide sites for water vapor condensation, and that these particles may well participate in initial condensation processes, field measurements demonstrate that contrail ice particles growing on entrained ambient particles begin to dominate in the contrail relatively soon.
Currently, global contrail coverage is a few tenths of a percent of the global surface or less, and is highly regional. The radiative impact is unclear because of uncertainties in this coverage and in the radiative effects of the contrails. According to estimates, however, their contribution to the total radiative forcing due to aircraft is comparable to that due to CO2, and thus can be considered to have a critical potential impact. Contrails, like high cirrus clouds, have a positive radiative forcing (warming effect), because they trap thermal radiation emitted from the Earth's surface more than they block incoming solar energy.
Equally important is the evolution of persistent contrails into high cirrus clouds that last for significant periods and have a positive radiative impact. Although individual instances of this phenomenon have been observed, the extent to which aviation increases cirrus cloud cover by this process remains highly uncertain. The effect is potentially one of the largest contributors to aviation radiative forcing. The impact on cloudiness from the accumulation of aviation aerosols at flight levels, whether or not a contrail formed initially, is another potential contributor. At present, the connection between airplane emissions and cirrus clouds is not well understood.

www.aiaa.org/aerospace/Article.cfm?issuetocid=14&ArchiveIssueID=5