I had seen totally unexpected landscape in the Thar desert: dry riverbeds with piles of broken rock, and vast stretches of level ground. Although large parts of the desert landscape was of this kind, there was a significant area full of sand dunes. I saw many dunes which were stabilized by plants specialized to grow in the desert, but there was a stretch of the great shifting dunes that deserts are famous for.
Dunes are formed by wind-blown sand. Sure enough, the air was dusty enough here that it felt comfortable if I pulled my tube scarf up to my nose to form a mask. Three kinds of sand dunes are commonly seen: barchans have horns facing away from the wind, parabolic dunes have horns facing the wind, and transverse dunes are perpendicular to the wind. What was I looking at? The great dune in the featured photo was clearly a transverse dune. I could sometimes see sand coming over its slip face. We were camped leewards of it. The ripples behind it were parallel to the edge. Eddies and gusts had formed smaller dunes, still pretty large, at its base. The photo above shows one of these. This was probably a blowout, or a parabolic dune. The horns at its end were not very long. In the picture above you can see that at the foot of the slip face the wind has tried to form yet another (tertiary) blowout dune. I guess this kind of fractal structure of dunes must be fairly common.
I woke up one morning to try to take photos of the dunes before sunrise, and found clouds blowing in. This was the first time I felt a strong wind. From the direction of the clouds it seemed that my guess was wrong: the clouds were blowing parallel to the dunes. The kind of clouds that you see in the photo are a high layer of cumulus clouds (altocumulus stratiformis). They form when ground-level winds carry moisture up where they freeze and then are carried in a different direction by high-altitude winds. So the direction of the movement of the clouds had nothing to do with the movement of the ground wind. In fact, because the ground wind had to be perpendicular to the movement of the clouds, my guess about the dunes had become more likely to be correct!
I had the warm fuzzy feeling which comes of the conviction of being right.