Strange Phenomenon

Here is a strange phenomenon that we recorded over the city of Thessaloniki in the northern Hellas. (Greece)
It was the 13th of July in 2009.

Although it seemed that there were some dark clouds, they were behaving so strangely that it gave us the creeps.

I am posting this because I would like very much to hear opinions and suggestions of what this might have been.

You can see more videos of the phenomenon in my website:

[Video 1 (July 13, 2009)
http://www.onirocosmos.gr/prototypi-erevna/apokryptografontas/178-periergo-fainomeno-vol1.html:3mh4pigb

[Videos 2 & 3 (July 13, 2009)
http://www.onirocosmos.gr/prototypi-erevna/apokryptografontas/179-periergo-fainomeno-vol2.html:3mh4pigb

And here is the same phenomenon recorded a year later, in the area of the Korinthian gulf in southern Hellas. It was July, 29th, 2010.
[Videos 4-6 (July 29, 2010)
http://www.onirocosmos.gr/prototypi-erevna/apokryptografontas/224-periergo-fainomeno-vol3.html:3mh4pigb

Sorry, guys. The video doesn’t seem to be playing properly in the forum.
Anyway, you can still see all the videos in the links above.