Large scale structures in the Sahara – what are they?
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