Explanation for contrail with a dark line

Question

I have recently taken a picture while on a walk, which is showing a phenomenon I cannot really find an explanation of.

A contrail was visible in the air, backed with a dark line that went all the way to the ground. The dark line was visible only for 1 minute, the sun was directly in line with the contrail. Though my first idea was to say it is a shadow, it doesn’t really make sense to me, because I would not expect the shadow to be loosely projected into the atmosphere. Also, a contrail does not seem to be dense enough for a dense shadow like this one.

The plane flying was a Boeing KC-135R Stratotanker, which can produce a large contrail with its four engines, which nevertheless could point to a shadow or weird refraction. Please help, I would like to know how this happened!

Time: August 3rd, 2:40 pm

Location: (53.118526, 9.198616)

Answer 1

You happened to be in the right place at the right time and the plane happened to be flying in just the right direction at that time. What you saw was the plane flying parallel to the shadow of its contrail.

Note that the contrail broadens a bit toward the top of the photograph. That's the older part of the contrail. The plane is located at the lowest white portion of the contrail. The part below that is the volumetric shadow of the contrail. That portion of the sky was relatively unlit compared to other parts of the sky, thereby causing the Rayleigh scattering that makes sky blue to be somewhat subdued. Because the plane was flying in just the right direction (flying to the northeast when the Sun was to the southwest), the shadow of the contrail was greatly enhanced.

Here's another image of a volumetric shadow of a human-made cloud, this time from the post-sunset launch of STS-98. In this image, the sun has already set on the ground, but has not yet set from higher altitudes. The very thick contrail of a Shuttle launch is well-lit higher up, and its volumetric shadow points right at the Moon. The Moon is close to full in this image, placing it very close to the anti-solar point. The anti-solar point is where parallel shadows appear to converge.