Large scale structures in the Sahara – what are they? In Google Earth we can see some very clear lines in the Sahara.  In the screenshot below you can clearly see these lines starting at the top going southward, then gently curving westward towards the bottom.

What are these structures and how were they formed?  Are they related to the wind?  Some sort of flow?  Are they surface structures or they are embedded deep in the rock?  Or something else?

I realize that this may be a trivial question for anyone with some knowledge of geology, but I really wasn't able to google up the answer.
These features are created by the wind.You will note that the upper left portion has a small dark spot. This is known as Waw al-Namus, or the "Oasis of Mosquitoes." It has a path of material in the same curved  manner as the surrounding features you mention.

From the link provided below:


  However, Waw al-Namus and its plume are not the only "wind records"
  in the area. As you utilise higher resolution images - of the order of
  1 km or better, other, somewhat different "long-term wind tracers" are
  revealed at almost every place across the Sahara Desert. These
  generally take the form of small-scale, long, parallel thin lines, as
  if being drawn across the desert by a giant pencil. One of the most
  spectacular places with long-term wind streamlines imprinted into the
  landscape can be found further southeast of Waw al-Namus, to the
  southeast of the Tibesti Mountains.


http://oiswww.eumetsat.org/WEBOPS/iotm/iotm/20060115_wind/20060115_wind.html