This air plane just caught my eye. Two contrails apparently are flowing backward

Question

This air plane just caught my eye. Two contrails apparently are flowing backward, slightly off-centered and then ultimately converge, giving the overall shape of a very narrow rhomboid parallelogram, with one diagonal being on the order of about four plane-width's.

Please explain what I am seeing here as detailed as possible.

Some of you may even know what class of plane this may be and thus infer the scales involved, to give some hints of the scale of the contrail under investigation?

I looked up other pictures, and if I am not mistaken, most contrails are slightly angled outward. Is this by design or due to expansion and convection of the gases involved? Can someone confirm this?

enter image description here

I did observe the described contrail-shape, with quite some consistency, over varying angles of ascension and declination.

I have never heard of conspiracies regarding contrails (e.g. chemtrails) until after writing this post. It shows that good, hard explanations for atmospheric contrail phenomena are in demand.

Given the right circumstances (large distances) some apparent contrail convergence can be attributed to perspective alone.

Links:

Contrail Science (impressive resource, which I just peeked at so far)

Contrail gallery

Contrails - clouds (ppt)

Explanation / Answer

The vapor pattern that we can see on this pictures is due to the instability of trailing edge vortices. Here are some picture showing an instability of this vortices (in French for English see aslo this JFM). Different plane will have different trailing edge vortices resulting in different observable vapor pattern. On Wikipedia the trailing edge vortex are revered as wingtip vortices. The geometry of the plane create a trailing edge vortices and this groupe of vortex are unstable causing the rhomboid parallelogram.

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