Video of Puzzling Phenomenon

Click on the above image to download and display the movie that displays a phenomenon that I am unable to fully understand presently.

The video was captured using an iPhone camera.  It shows a view of the ground taken through the window of a Delta Airlines flight from Phoenix to Atlanta at 1300 hrs Phoenix time on 12 Jan 2010.  The sky was clear. 

In the video, you can see a bright circle moving over the ground followed by a dark line.  The dark line is, I believe, the shadow of the contrail presumably being generated by the aircraft. 

The bright circle is what I find puzzling.  As it moved across the ground, it brightened dirt, trees, etc.  Vehicles that were within the bright circle glowed brightly red or blue or green (whatever color they were painted presumably).  They seemed to fluoresce.  The camera I used did not pick this up.  Snow fields did not seem to brighten noticably. 

The bright spot was just in front of the contrail shadow and apparently coincident with a straight line from the sun through the aircraft to the ground, i.e., the sun, the aircraft, and the bright circle lie on a straight line. 

So my question is what is the cause of the bright circle? 
  1. A diffraction effect caused by air being compressed by the aircraft?  Sort of a lens effect?
  2. Normal specular reflection?  (Why would the light appear to be focused?)
  3. Something else?
I am dissatisfied with any hypothesis I have been able to come up with. 

Please help. 

Explain why this bright circle exists and the explain physics of this phenomenon.