On May 28, 2004, a massive dust storm was sweeping from the northeast corner of Chad to its western border, a distance of roughly 900 kilometers (560 miles). The dust storm appears to be originating in the Depression du Mourdi behind the dark semi-circle of the Ennedi Mountains in northeastern Chad. Near its origin, the airborne dust is easy to see against the darker orange of the ground. As the dust spreads across the country and into Niger in the west, the dust becomes harder to see. The problem is not unique to this image—dust storms are often hard to spot in satellite imagery unless the dust is blown over water or some other feature that is a different color than the dust.
Looking at surface temperatures can make dust storms easier to see. The Moderate Resolution Imaging Spectroradiometer (MODIS) sees the dust, but not the ground beneath it. Lifted by the wind into the cooler atmosphere, the dust is 25 to 30 degrees Celsius cooler than the ground, and it appears as a “cool” streak across the image. The land temperature in this image reaches up to 67 degrees C (150 degrees F) in pockets where the land is darker, and therefore, absorbs more sunlight. Patches of clouds also show up as extremely cold blue regions in the temperature image.
The temperature image highlights some features of the dust storm that are not as clear in the true-color image. The storm appears to be much wider and extend much further into Niger in the land surface temperature image. Near the origin of the storm, rising and falling air is making ripples in the air-borne dust. The ripples are visible in the true-color image, but their structure is more distinct in the temperature image.
The surface temperature image was generated based on a stream-lined version of the MODIS Land Surface Temperature product. The countries shown in these images include, from left to right, Niger, Chad, Libya (top right), and Sudan.