Photo C: What mechanisms most likely account for the dense trails following the plane, and the rainbow spectrum in between?
The dense trails: Highly favorable upper-troposphere meteorological conditions in which the plane is flying (e.g., moist air that is supersaturated with respect to ice, unusually low temperatures, wind shear to help spread the persisting contrails); the jet has 4 engines, so extra emissions of carbon particulates and water vapor around which contrails can form; the aviation fuel may have a higher sulfur content than newer fuels, etc.
thin layers of ice or water particles caused by contrails off of the tail. simple optics.
This is obviously a combustion contrail.
Ambient air very near 100% saturation. Rainbow spectrum due to an optical effect from spherical liquid droplets of appropriate size.
temperature, possibly amount of sulphur in the jet fuel, light scattering from ice or other crystals
the aircraft is flying through a very moist region of the atmosphere (RHice >100%) and generating very heavy condensation trails. Moisture levels are so high that uniform-sized ice crystals are forming in the pressure wake of the aircraft fuselage and are scattering solar radiation to produce the atmospheric optics seen in the photo.
The rainbow is a feature of light scattering through droplets and depends in part of the size and number density of the particles. It is a single-scattering phenomenon that breaks down when there is multiple scattering, meaning lots of droplets (thicker clouds). The dense trails would indicate, to my anyway, that the exhaust contains a lot of particles upon which droplets form when injected into a cold, relatively humid environment.
Engines are producing a dense contrail due to high water vapor content of exhaust and ambient air producing mixing supersaturation. Aerodynamic contrail is formed by the wing. These are probably producing liquid droplets which a refracting light like a rainbow.
Wing induced vortices role up most of exhaust from left wing and right wing engines, respectively.
Vortices shed some particles that fill the gap between, solar scattering form less optically dense ice particles produce a rainbow.
When the vortices in the wake of the aircraft role up all exhaust gases (Water vapour (H2O), Carbon Dioxide (CO2), Nitrogen Oxides (NOx), etc. are concentrated in these vortices until they become instable (Crow-Instability) and dissolve. The rainbow spectrum can be explained by very evenly sized water or ice particles.
The dense trails are persistent contrails. The rainbow spectrum in between is an example of Iridescent aerodynamic contrails (AerC). AerC can be differentiated from jet contrails as soon as they display iridescence which requires an angular distance from the sun of less than about 30°.
Contrail formation in relatively humid air. The rainbow is probably an optical phenomenon due to the presence of nearby ice crystals.
As can be seen below the aircraft, there are wide spread clouds, indicating that this is already a region of high humidity. The contrails are particularly dense because not only are most of the emissions particles forming ice crystals, but the thermodynamic and dynamic forcing caused by the aircraft emissions and wake turbulence are activating natural aerosols as well. As can be seen by the reflection on the aircraft fuselage, the sun is to the upper left and is causing a rainbow to form by refraction from the light passing through the evaporating ice crystals between the contrails.
This picture is taken close to the aircraft, whereas the previous pictures are taken from the ground, a few thousand feet away. It perhaps could be the type of jet fuel that is not burning clean. The water droplets happen to be at favorable sun and view angles where rainbows are seen.
Very high gradient between temperature and moisture of exhaust and that of ambient atmosphere. This causes explosive condensation and even convection along the boundaries of the trail. The rainbow is simply caused by sunlight refraction through the edges of the trails passing through to the middle area. (I have this photograph on my wall in my office)
The jet aircraft is flying through a region that is already at very near saturation, and thus, very dense contrails were formed. The "rainbow spectrum" of colors is caused by the geometry of the sun angle and view angle of the observer, and is very much a similar phenomenon as seen in halos, rainbows, sun dogs, etc.
Angle of illumination, photo-manipulation of contrast
Atmospheric conditions such that the cooling exhaust jets (which contain water from the fuel combustion) become rapidly supersaturated with respect to liquid water produce the dense contrails (with the sulfur or soot content of the exhausts playing a contributing role by increasing the number of water droplets produced). Nearly spherical ice crystals of appropriate size can lead to the "rainbow spectrum" just as raindrops lead to rainbows.
I am actually more intrigued by the interaction of the engine contrails with the wake vortex that causes the inboard and outboard contrails to wrap around each other. Back to the issue at hand. I tend to think of contrails as composed of ice, but there are some made of ice and some made of water and some that appear to have components of both. I would speculate that the iridescent region between the contrails may be the same phenomenon that produces rainbows. The refraction (and near retroreflection) of light through roughly spherical water droplets spectrally resolves sunlight into its components. Given my estimate of the direction of the apparent sunlight, however, this may be related to a halo that originates with ice crystals rather than water droplets.
The dense trails are contrails, line shaped clouds forming behind an aircraft if the ambient air is cold enough. The rainbow spectrum are due to the formation of Iridescent aerodynamic contrails.
the same phenomenon as a rainbow, sunlight is refracted by water droplets
always the same answer. Presence of trail is due to the humidity of ambient air at the flight level. Hear probably, humidity of ambient air is very close to 100%. All water from Kerosene combustion become cloud. Impossible to discuss about the rainbow without information concerning alteration of original picture. Cloud colors below are also unusual
the quality of the photo is insufficient to see the full rainbow spectrum
Possible that the air in the jet exhaust is wet enough to nucleate water droplets, contributing to the colored glory between trails.
My guess is that this plane is flying at a level that is supersaturated, so that once condensation nuclei are activated, the clouds grow.
The dense trail is a normal exhaust contrail formed by the water vapour from the engines, the rainbow-coloured trail in between is likely due to aerodynamic effects (aerodynamic contrails).
Standard contrail formation, and probably optical refraction for the rainbow.
The air must be very humid to support the persistent dense contrails. I'm not certain about the origin of the thin layer of ice crystals between the contrails, but most likely the colors are refraction of light that separates the colors, similar to a rainbow. Actually, the most closely related common example is probably when one looks at the moon through very thin cirrus cloud, and a rainbow of concentric rings is seen as the moonlight is refracted to the observer's eye by passing through hexagonal ice crystals where each color is refracted by a different angle (called a "moondog") This is sort of like how rainbows form, except rainbows are reflected light in liquid water drops, whereas the moon phenomenon is light passing through ice crystals.
Very thin "subvisual cirrus" is very common in the upper troposphere (that is, very low concentrations of ice crystals in highly ice-supersaturated air). My guess is that there is a layer of not-very-obvious optically-thin cirrus throughout this scene, but it only becomes apparent between the contrails in the photo because the contrails are highly reflective and throw extra light onto the cirrus ice crystals so that their reflected light is visible at the location of the camera.
Most of the trails is water vapor, the colors resulting from scattered sun light. The back of the aircraft is lit by sunlight so the light colors are caused by forward scattering.
Aircraft exhausts provide cloud condensation nucleii that form cloud droplets. Some droplets evaporate to a size that is not identifiable by eye. These droplets are still optically active at visible wavelength and create the observed spectra.
These are contrail forming in the wake of the aircraft engines, from aircraft emitted and the ambient water vapour. The coloured structures between the contrails are likely to be aerodynamically formed contrails of less ice water content but different crystal structure. The are well investigated examples of this kind in the literature.
Large ice crystals has 22 degree rainbows. Notice the red-edge starts cutting across the contrail where the large ice particles are falling out. The angle is because of the sun angle.
I don't see a rainbow spectrum in the photo. I see a blueish region and a pink region. The pink region appears to more or less of the same color as the surface of the underlying cloud deck. The sun is at a rather high altitude, but located "behind" the aircraft on the photo. What we "see" is a rather small section of a glory, which is an optical phenomenon well described for cloud decks. The rather complicated pattern of the cloud droplet layer between the 2 pairs of sub-contrails lead to the funny shape of the glory.
Very high humidity, much greater than ice supersaturation, in the layer results in formation of dense contrails. The faint flat trail in the middle is likely the secondary contrail formed by the detrainment of part of the wake vortices. The small particles and thinness of the center contrail together with the viewing and illumination angles can result in a "rainbow" effect. formation of an airframe contrail induced by the reduced air pressure on top of the wing.
Different types of contrails: spectrum contrails from Aerodynamic effect, others from normal Schmidt Appleman formation
The dense trails are due to ice nucleation in a region of supersaturation with respect to ice. The rainbow is an optical effect due to the formation of hexagonal shaped ice crystals
contrail are ice crystals and under the right angles on light act like a prism.
The contrails from the four aircraft engines are aerodynamically combined to two main contrails. The thickness and the persistence is again dependent on the atmospheric ice supersaturation.
Amount of ice crystals
diffraction of light
Air was supersaturated.
The environmental conditions are humid and cold and the engines are generating turbulence. The rainbow is the result of sunlight being dispersed (separated into its component wavelengths) via its interactions with ice crystals in the exhaust.
Plane is flying in nearly saturated air with insufficient condensation nuclei. The colors result from light scattering by small cloud particles that develope in the turbulent wake of the plane.
High humidity and the distribution of temperature and vapor behind the engines, respectively. The rainbow might indicate a less dense suspension of water droplets, as it normally forms during rains or next to waterfalls
Not convinced that the photograph is not retouched.
Formation of liquid droplets and ice crystals. Both droplets and ice crystals can act as "prisms" that can give the rainbow spectrum
The phot shows 4 exhaust contrails forming from engine emissions and in addition a thin ice cloud forming because of low pressure over the wings in ambient air that is very humid and cool (so-called aerodynamic contrails)
See publications by Gierens et al. (2009) dn Kärcher et al. (2009):
It seems that the plane is flying in air of very high humidity (maybe in the tropics). Many ice crystals are formed in the contrails that take up a large amount of water vapor. At the same time it seems that there is some kind of trail inbetween the main trails that account for the rainbow colors which would mean that aerodynamic contrails have formed as well. The rainbow color in aerodynamic contrails have been shown to indicate the size of the ice crystals. As the crystals grow the color changes so that there is a spectrum of colors in different distances from the air plane
The wings produce lift and hence above the wing the pressure is low. Hence the air flowing over the wing is cooled adiabatically, reaching fast large supersaturation and and hence forming of many small ice particles. Optical refraction leads to the nice colour spectrum.
Caused by condensation of humid air on the engine exhaust particles. The colors are caused by variations in the hydrometeor size and are visible due to the scattering angle of sunlight to the camera
