What determines stratiform/cirrustratiform or cumuliform contrails?

[calm_days]

I recently saw that one type of large airliner again that produces the cumuliform contrails that we remember from when we were younger, and so i checked on wikipedia to see if there is any meteorological explanation for what determines the cloud form resulting from condensation trails. 

Quote

Persistent contrails are of particular interest to scientists because they increase the cloudiness of the atmosphere. The resulting cloud forms are formally described as homomutatus, and may resemble cirrus, cirrocumulus, or cirrostratus, and are sometimes called cirrus aviaticus.

So, there is just partial information on wikipedia, but i am sure some people on here might be able to explain or accurately speculate!! 

A slight tangent that is also highly relevant to all of us as actual professional and amateur meteorologists:

Because persistent contrails are the cause of claims of you-know-what-trails, I continue to sincerely wish that NASA would help to put an end to that conspiracy theory, which negatively impacts the mental health of potentially 100,000s of people, by revisiting the Atmospheric Effects of Aviation Project suite of information, and producing a modern "explainer" about the persistent clouds!! 

https://web.archive.org/web/20000520093129/http://hyperion.gsfc.nasa.gov/AEAP/AEAP.html

It is definitely time to update this for the 21st century, as it is one of the more interesting NASA atmospheric science inquiries that has ever existed. 

[calm_days]

I guess this could be part of it?

https://web.archive.org/web/20000608111808/http://hyperion.gsfc.nasa.gov/AEAP/gandrudabs.html

 

Contrail Microphysical Comparisons For HI/LO Sulfur During Success

Bruce Gandrud, Cynthia Twohy and Darrel Baumgardner

During the NASA SUCCESS campaign different levels of fuel sulfur were burned in the NASA 757. The contrails from the 757 were sampled with the suite of instrumentation on the NASA DC8. A counterflow virtual impactor (CVI) was flown with water content and condensation nuclei routinely monitored.

The results clearly show higher Total Ice Conc and higher Ice Conc-Volatile nuclei in the high sulfur fuel case. These results along with Ice water content and complimentary particle measurements will be presented.

Another submitted paper titled "Ice-forming Particles in Aircraft Exhaust" by Twohy and Gandrud is closely related to this work.

[calm_days]

this seems partially relevant as well, adding some details and context to the above, and trying to answer my own question!!

 

The Role of Fuel Sulfur in Controlling Aircraft Emissions of Volatile Aerosol Species

B. Anderson, W. Cofer, G. Gregory, H. Wallio, D. Bagwell, and G. Nowicki
NASA Langley Research Center
Hampton, VA 23681
 

We report measurements of total and nonvolatile (at T ž 290°C) aerosol emission indices made 0.1 to 15 km downstream of the NASA Langley B757 aircraft alternately burning fuels containing ~70 and ~700 ppm sulfur. The flights were conducted as part of the NASA-sponsored Subsonic Assessment: Cloud and Contrail Effects Special Study, held in Salina, Kansas during April - May 1996. Data were obtained from aboard the NASA Wallops Flight Facility T-39 Sabreliner aircraft which had been instrumented with a suite of meteorological and trace gas/aerosol sensors, including capability for CO2 determination and coarse sizing of particles in the 4 nm to 3,000 nm size range. To obtain fuels with identical hydrocarbon matrices, the ~700 ppm sulfur fuel was created by introducing a sulfur additive to the ~70 S fuel. The resulting low and high sulfur content fuels were loaded in the B757 left and right wing tanks, respectively. Then, with the B757 fuel flow system, both engines could be fed from either wing tank or the individual engines could be fed with fuel from their respective wing tanks, thus making it possible to burn low and high sulfur fuel simultaneously. Exhaust plume measurements were recorded on two separate flights at altitudes ranging from the surface to > 13 km and under a variety of atmospheric conditions.

Although nonvolatile aerosol (presumably soot) production was essentially equivalent, very distinct, engine independent differences in volatile aerosol emission indices were observed in combustion of the low and high sulfur fuels. These differences were most pronounced in the ultrafine size range (4 to 20 nm diameter particles) where a 10 to 20 times greater normalized number density of particles were observed in the high S plume. Indeed, only in contrail-producing situations were exhaust plumes from combustion of the two fuels distinguishable based on emission indices of larger particles (>20 nm). At cruise altitude and under contrail-forming conditions, we estimate, based on an inferred size distribution and assuming the particles are composed of 70:30 w/w sulfuric acid:water, that on the order of 15% and 8% of the fuel sulfur was converted to aerosols in the near-field aircraft exhaust plume in high and low sulfur fuel cases, respectively.

i've not been able to find this online yet but based on the title, i do think it also would have some information relevant to this topic!! 

A. Ackerman

Secondary Ice Nucleation in Persistent Contrails

[calm_days]

This one is really interesting also, presented at the 1998 AEAP conference: i do not want to post every single relevant study, but, this is definitely a valid contribution to this overall topic!!

 

A Numerical Study of Aircraft Wake Induced Ice Cloud Formation

 

Klaus Gierens and Johan Stroms
DLR, Institut Physik Atmosph
D-82234 Oberpfaffenhofen, Germany
Department of Meteorology, Stockholm University,
S-10691 Stockholm, Sweden

Aircraft condensation trails are usually thought to form mainly from condensation of ambient water vapor onto soot and other aerosol particles that originate from the fuel combustion in the jet engines (e.g. K\"archer et al.1996). However, aircraft are also able to produce large concentrations of ice crystals without involving exhaust particles. An example of such a phenomenon, termed APIP (Aircraft Produced Ice Particles; see e.g. Rangno and Hobbs, 1983; Sassen, 1991; Foster and Hallett, 1993) occurs when an aircraft moves through a super-cooled cloud. The mechanisms thought to be responsible are splintering on leading surfaces and adiabatic cooling near the aircraft and propeller tips.

It is interesting to note that the mere disturbance of the air by the aircraft is able to form cloud particles. Aerodynamic cloud formation might not be restricted to temperatures warmer than -30~\Celsius, for which the APIP phenomenon has been studied so far. In the temperature range between -30 and -60~\Celsius\ which corresponds to the crusing altitudes of commercial airtraffic, the most important ice nucleation process seems to be freezing of haze droplets at relative humidities near water saturation (i.e. above ice saturation). Thus, is it possible that the turbulence alone from an aircraft flying through a metastable atmosphere, with reference to humidity, can form an APIP trail? The magnitude of the vertical air motion caused by the trailing vortices behind a big airliner can be on the order of meters per second, which results in very strong turbulence (evident to anyone who have been flying close behind an other aircraft). If an airparcel in the wake of the aircraft is lifted to the point where the humidity is increased enough for homogeneous freezing to occur, a cloud would rapidly form.

To test the hypothesis: that it is possible for an aircraft to form a contrail by the aerodynamic effects from the aircraft alone, we have performed numerical simulations of ice cloud formation in the wake of an aircraft flying at cruise altitude. The engine exhaust has been excluded from the simulations in order to study cloud formation due to aerodynamic effects. The ice is formed via homogeneous freezing nucleation of ambient haze droplets in the upwelling limbs of the vortex pair behind the aircraft. Properties of wake ice clouds are compared with properties of contrails obtained with in situ measurements and recent simulations. In particular, we find that aerodynamically induced ice clouds are similar in microphysical and radiative respects to contrails that are formed from the nucleation of exhaust particles. The results show that significant fractions of contrails as young as 2 to 5 minutes may originate from aerodynamic effects and not only from nucleation of the exhaust particles.

 

Spreading and Growth of Contrails in a Sheared Environment

Eric Jensen, Andrew S. Ackerman, and Owen B. Toon

The evolution of persistent contrails has modeled over time-scales of 15-180 minutes using a large-eddy simulation model with detailed microphysics. Model results have been compared to satellite and in situ measurements of persistent contrails from the SUCCESS experiment. In particular, we simulated the evolution of the persistent contrail observed on May 12, 1996. In simulations with large ambient supersaturations and moderate wind shear, crystals with lengths > 200 microns are generated within 35 minutes by depositional growth. In situ measurements in the May 12 contrail case showed that these large crystals did in fact form. The large crystals fall rapidly and the contrail horizontal extent increases due to the wind shear. Strong radiative heating (with rates up to 30 K/day) drives a local updraft and lofts the contrail core several hundred meters. The observed rate of contrail spreading and maintenance of optical depths larger than 0.1 can be explained simply by growth and precipitation of ice crystals nucleated during the initial contrail formation if the environmental humidity is high enough (relative humidity with respect to ice > 125%). This result is consistent with observed high humidities in regions where the persistent contrails formed on May 12. Also, the simulations indicate that the humidity must be high throughout a depth of at least several hundred meters below the contrail to allow the crystals to continue growing as they fall.

 

this is from the 1999 AEAP conference!!

 

OBSERVED CONTRAIL-CIRRUS FORMATION CONDITIONS AND IMPLICATIONS

Ulrich Schumann,

Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Physik der Atmosphäre,

Oberpfaffenhofen, 82230 Wessling, Germany, email: [email protected]

 

According to the Schmidt-Appleman criterion, contrails form below a threshold temperature or above a threshold altitude in the troposphere. The threshold temperature is engine dependent. The extended Schmidt-Appleman criterion accounts for the so-called „h -effect" where h is the overall propulsion efficiency of the engine/aircraft combination (Schumann, 1996, Meteor. Z., 5, 4-23), i.e. the fraction of combustion heat used to provide the work to propel the aircraft against its drag. For large h , the engine exhaust temperature-/humidity-excess ratio is small and mixing with ambient causes contrails at higher ambient temperature than for low h , since only the fraction (1-h ) of the heat but all of the H₂O from the fuel combustion leaves the engine with the exhaust gases. The efficiency h of present engines is expected to increase with better technology in the future, and future aircraft cause contrails over a larger altitude range. Persistent contrails form in ice-supersaturated air masses. Aircraft induce cirrus in weakly ice-supersaturated air masses where no cirrus would have formed otherwise.

These findings, as discussed in chapter 3 (with D. W. Fahey et al.) of the forthcoming IPCC report, are of importance in assessing the climatic impact of contrails, and caused considerable debates. This paper reviews the arguments and provides new data to support the findings.

Recent contrail observations with ambient temperature and humidity measured (with J. Ovarlez) during the POLINAT 2 project provide further evidence for the importance of engine efficiency for contrail formation. The observed contrails can be explained only when the theory includes the „h -effect". Engines with high propulsion efficiency cause contrails where engines with low efficiency would cause no contrails.

A spiral contrail observed in NOAA-AVHRR-satellite data of more than 1500 km length and more than 1.7 hours age provides evidence that contrails form in regions where otherwise no cirrus clouds form.

Statistics of upper tropospheric humidity derived (with K. Gierens) from data obtained within the MOZAIC project (Marenco et al., 1999; Helten et al., 1999) show that airliners fly about 15% of their time in ice supersatured air masses. The ice supersaturation is often too low for natural cirrus particle nucleation. Direct intercomparison of MOZAIC and POLINAT measurements support each other (Helten et al., submitted, 1999). Ice supersaturation occurs frequently in the upper troposphere in the North Atlantic flight corridor, at least during the September/October 1997 POLINAT-2/SONEX experimental period.

The MOZAIC data and the POLINAT data imply that the ice water content of contrails raises about exponentially with temperature. Hence, contrails forming at lower altitude and higher ambient temperature are optically thicker and radiatively more effective than contrails at higher altitudes.

Preference for Presentation: oral

Topic Area: Contrails might deserve a special session, but this paper could fit to the session „Atmospheric Observations".

 

also from 1999, a short abstract but with some helpful context!!

 

Perturbation of the aerosol layer by aviation-produced aerosols:

A parametrization of plume processes

 

B. Kärcher, DLR Institut für Physik der Atmosphäre, Germany

S.K. Meilinger, Max-Planck-Institut für Chemie, Germany

 

 

The perturbation of the sulfate surface area density (SAD) in the tropopause region and the lower stratosphere by subsonic and supersonic aircraft fleets is examined. The background aerosol surface area, the conversion of fuel sulfur into new sulfate particles in aircraft plumes, and the plume mixing with ambient air control this perturbation.

 

The background aerosol surface area is enhanced by the addition of ultrafine aerosol particles at cruise altitudes. The study includes recent findings concerning the formation and development of these particles in aircraft plumes. Large-scale SAD enhancements become relevant for background SAD levels below about 1-10 mm²/cm³, even for moderate sulfate conversion fractions of 5%.

 

Results from an analytic expression for the surface area changes are presented which contains the dependences on these parameters and can be employed in large-scale atmospheric models.

 

[calm_days]

Here is a recent study from last year!!  i think this is helpful too, and i'm glad to know that many people here will be interested in reading about these phenomena. 

Again as professional and amateur meteorologists, we have been seeing the differences in clouds including persistent contrail clouds for some time, and have been aware the additions to the cloud atlas relating to them, and have not assigned pseudoscientific concepts to them, but were also are lacking scientific context as far as what the changes might be!!

Importance of Secondary Ice Production to Ice Formation and Phase of High-Latitude Mixed-Phase Clouds during SOCRATES and MARCUS

 

atmospheric sciences

cloud physics

• Xi Zhao,
• Xiaohong Liu,
• Vaughan Phillips,
• Sachin Patade,
• Minghui Diao,
• Ching Yang,
• Neel Desai

Abstract

Measured ice number concentrations are often much higher than the number concentrations of ice nucleating particles (INPs) in moderately cold mixed-phase clouds, suggesting the potential importance of secondary ice nucleation (SIP). However, the occurrence frequency and importance of SIP relative to primary ice nucleation for ice formation and mixed-phase cloud properties are largely unknown. Representing the SIP processes in weather and climate models is equally challenging. In this study, we present a process-level understanding of SIP in high-latitude mixed-phase clouds based on integrated model-observational analyses of the NSF SOCRATES aircraft and DOE ARM MARCUS ship-borne data. We run the Community Earth System Model version 2 (CESM2) nudged towards the MERRA2 Reanalysis and output the modeled clouds and aerosols along the aircraft flight and ship tracks for direct model-observation comparisons. We found that CESM2 with a physical representation of SIP processes (e.g., ice-ice collisional break-up, droplet shattering during rain freezing) better capture the observed ice crystal number concentrations (ICNCs) and cloud properties. SIP often dominants the ice formation in the moderately cold mixed-phase clouds, and transforms ~30% of pure liquid-phase clouds simulated in the model into mixed-phase clouds. We also compare modeled ice enhancement ratio due to SIP to ICNC and INP number concentrations observed during SOCRATES and MARCUS.

[calm_days]

Cirrus Cloud and Climate Modifications due to Subsonic Aircraft Exhaust

 

Key Investigators: Eric J. Jensen, Owen B. Toon

 

NASA has recently initiated a program to evaluate the potential effects of current and future commercial aircraft fleets on atmospheric chemical processes and climate. As part of this program, we are modeling the effects of subsonic aircraft exhaust on upper tropospheric cirrus clouds. Using sophisticated computer programs, we have developed a detailed ice cloud microphysical model here at NASA Ames Research Center. The model simulates cloud processes such as ice crystal formation, growth, and transport. The formation and evolution of aircraft-generated contrails is simulated to determine what processes and environmental conditions control the growth, spreading, and dissipation of contrails. In addition, the formation of natural cirrus is simulated with and without aircraft exhaust soot particles to predict the impact of commercial air traffic on the frequency of cirrus occurrence and their impact on climate.

Recent observations of cirrus clouds have shown that clear air in the upper troposphere is often supersaturated with ice. Cirrus do not always form in these regions due to the lack of natural nuclei to provide a foundation on which ice crystals form. If aircraft exhaust soot particles are efficient ice nuclei (as shown in Fig. 1) ,

then the frequency of cirrus may be significantly enhanced in regions with heavy air traffic (see Fig. 2) .

 

As a result, the aircraft exhaust may increase the frequency of cirrus occurrence and increase the number of ice crystals in cirrus. As cirrus clouds absorb infrared radiation emitted by the Earth's surface and reflect sunlight, changes in cirrus properties would produce heating of the upper troposphere and cooling at the surface. Also, precipitation of cirrus ice crystals removes upper tropospheric water vapor. Because water vapor is a very important greenhouse gas, changes in cirrus and the upper tropospheric water vapor budget due to aircraft exhaust may substantially influence climate.

 

Currently, the properties of soot generated by aircraft exhaust are not well understood. We do not know how effective these particles are as ice nuclei. We are using our cirrus cloud microphysical model to simulate the impact of soot particles on cirrus cloud frequency and climate for a wide range of assumptions about the soot properties. We are evaluating these effects for a range of environmental conditions, including cirrus anvils generated by strong convective storms and thin cirrus generated in fair-weather conditions. A final determination of the exhaust impact on cirrus and climate will require aircraft observations of natural and anthropogenic upper tropospheric particles, laboratory studies of ice nucleation on soot particles, and numerical modeling of the formation of cirrus altered by exhaust soot particles.

 

Figure 2. Image courtesy of Steve Baughcum (Boeing Aircraft Co.), Don Maiden (Langley Research Center), and M. Metwally (McDonnell-Douglas Aircraft).

 

i partially remembered reading this many years ago.  (Although this is old information, it would be very relevant in NASA et al figuring out how to produce a new suite of information that would help people to know why clouds do what they do, including the new types of clouds and activity. 

I think on some level the complexity of the PR (eg. would the airlines themselves be involved?) is simply not something that NASA et al necessarily previously had the time to do.  However, i think their social media teams at this point and forward, are very much able to figure it out, with some patience and problem-solving.) 

[Stormchaserchuck1]

The worst I've ever seen them was Sedona, Arizona. +2,000 in the sky

[calm_days]

Yes, eventually i learned that contrails are more likely to become persistent in between weather systems and there are various interstitial areas between systems that cover a lot of area. 

This is part of what causes humans to say that it's chemtrails, because the likelihood of persistents has increased, and they do often look unusual and due to variations/differences in condensation nuclei for a variety of reasons, the cloud matter often has the appearance of the sun's brightness instead of stopping the progression of the sunlight.

~~

Regarding the Atmospheric Effects of Aviation Project, i do think it's important on some level, not likely exceeding this thread's existence, to consider that supersonic civilian aircraft were a real consideration back then (mid to late 1990s).  Supersonic civilian transport aircraft are possibly returning at some point in the 2030s.  What types of contrails and thus also cloud formations might result from their return??  As far as teleconnections, due to their higher altitude, would the effects be neutral or distinct?? 

It isn't something that i find to be of concern, but, it seems like it would be something that would be noticable whether it is addressed in any official press releases preceding the return of supersonic air travel. 

NASA Goddard was studying the climatological effects of supersonic planes' contrails at the full level of their collective knowledge back then, indicating that it would not be an insignificant potential in the future as well.