What's the sudden brightness change in the timelapse from the AsiaSat launch?

Factual Questions
#1

During the most recent SpaceX launch, a timelapse photo of the trail left by the rocket was made. http://img.new.livestream.com/events/000000000031d6a7/93d34713-b8a1-4e7a-bdd8-f52c2580b004.jpg

This image is pretty awesome to look at, and it’s virtually a 3 dimensional graph of thrust angle and magnitude versus altitude.

What’s with the large change in the middle there? Is that the throttleback near max Q or just an artifact of the way this image was taken?

#2

I am going to guess it is when it passes through a cloud layer . The light is scattered by the vapour particles, lighting up that part of the cloud. It is known as the Tyndall effect.

#3

Yes, it looks as if it lines up with the bottom of that thin layer of cirrus cloud at the top of the image. The portion of the trail above that point is seen through the cloud.