Calm before the Dust Storm

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This striking true-color image shows a clear view of the Cape Verde Islands in the eastern Atlantic as a massive wall of Saharan Desert dust (tan pixels) is fast approaching from the east. In this scene, the Cape Verde Islands sit in the middle of a large area of sunglint, which refers to the bright patch of water around the islands where a lot of sunlight is being reflected directly up at the satellite. Notice the �wind shadows� tapering away from the leeward (southwestern) side of the islands. These dark streaks are caused by the islands� disturbances to the prevailing wind pattern, causing small patches of calm. Behind the islands, where there is less wind, the ocean is relatively much flatter and so much less sunlight is being scattered back up toward the satellite, thus making the water appear darker.

This scene was acquired on February 3, 2004, by the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA’s Terra satellite. The image is available in additional resolutions. Terra imagery acquired over this region three days later (February 6) shows the dust plume entrained in a strong southerly air current and stretching out in a vast arc extending more than 2,000 km.

Image courtesy Jacques Descloitres, MODIS Land Rapid Response Team at NASA GSFC

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