A palette of tans and white, with a small splash of blue, painted a stunning scene as NASA’s Terra satellite passed over Chile, Bolivia, and the Pacific Ocean in mid-July 2020. The Moderate Resolution Imaging Spectroradiometer (MODIS) on board that satellite captured the scene, which contrasts moisture and aridity, on July 12.
The many shades of tan range from cream to khaki in Chile’s Atacama Desert, along the coast, to camel and taupe on the high plateau of the Bolivian Altiplano (inland). These Earth tones, with barely a breath of green, marks the extreme aridity of the entire region.
The Altiplano, which rises to an average height of about 3,750 meters (12,300 feet), cradles the largest salt flat in the world – the Salar du Uyuni. The Salar du Uyuni spans 10,000 square kilometers (3,900 sq. mi) and wears a thick crust of minerals, giving it the bright white appearance. The only evidence of moisture on land is a small salt-crusted lake in the northeastern corner of the image.
The region of the Salar de Uyuni is considered a cold desert, receiving minimal rain each year. In the west, Chile’s Atacama Desert is not only one of the driest places on Earth, it is also extremely hot. The heat and dryness ends dramatically at the coastline. It’s hard to think of a moister environment than the Pacific Ocean, covered by moisture-filled stratocumulus clouds. In just a few spots the cloud creeps over the coastline, offering slight moisture to the Chilean desert.
Marine stratocumulus clouds are low-altitude clouds typically found off the west coasts of continents, particularly Chile. But they also occur off the coast of California, Namibia, and to a lesser extent off the coast of Portugal and western Australia. These clouds form at low levels over relatively cool ocean water, in a region where the air above is gently descending. The descent dries the higher-altitude air and prevents clouds from forming there, and produces a temperature inversion about a kilometer above the surface. Near the surface, water evaporates from the ocean and gets mixed upward by turbulence. It reaches the inversion—which puts a lid on further ascent—and the air cools and saturates, forming the cloud deck.
The large deck of cloud is only broken in a few areas, allowing a splash of blue ocean to show near the coast of Chile. A larger area of Pacific Ocean blue can be seen in the far west (left) of the image. This is an area of “open cells”, that can form when drizzle occurs or possibly due to interaction with aerosols.