Tuesday, October 8, 2013

Contrail Shadow

Here is an amazing picture sent to me by Bill Anderson showing the shadow from an aircraft contrail on a lower cirrostratus cloud deck.  The picture was taken around 9 AM from near Lake Union and the aircraft was moving to the northwest.  Bill determined it was an Asiana 747 flying at 36,000 ft. The laser ceilometer at Sea-Tac indicated that the cloud deck was much lower (about 25, 000 ft).  It looks like the aircraft is lower than the clouds, but that is not the case.

 
There was an amazing alignment of the flight path and the shadow...that does not have to happen. Take a look at a blow up of the aircraft, shadow, and contrail.


You can get feeling for the geometry of such shadow from the following schematic (for moon light, but sun light is the same idea):




And here is an example of a view of a contrail shadow from above.



Bellingham Talk on October 15th
I will be giving a public talk on "The Future of Weather Forecasting" in Bellingham on October 15th.    In this talk, I will discuss the development of weather prediction from folk sayings to numerical weather prediction, and will describe what I think will happen over the next decades.  For more information, go here
 




1 comment:

Jon Nelson said...

It is also possible that the shadow part is a negative contrail in which the vapor and gases dry out the cloud.

I see these occasionally, but have never seen one abruptly go from negative to positive.

So, both explanations have a coincidental nature to them. I'd favor your explanation, though the negative contrail is also possible.