The photo above showing a sensational display of lenticular clouds was snapped near La Rioja, Argentina, at the base of the Andes Mountains, on September 9, 2011. I was doing seismic testing just after sunrise and was taken aback by the gold and tawny wave clouds that appeared across much of the sky. Photographer: Hector Fabian Garrido
These lenticulars took shape to the lee (east) of the Andes, just west of my location — the Sun was behind the camera. Lenticular clouds are generally orographic in origin, forming in lee waves when air is forced to rise over elevated terrain. On this early spring morning, the smooth structure of the waves, the illumination by the low Sun, and the absence of other types of clouds, gave the sky a surreal look.