May 23, 2013 - Ship-wave-shape wave clouds induced by the Azores

Ship-wave-shape wave clouds induced by the Azores

The Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA’s Terra satellite passed above the North Atlantic Ocean on May 15, 2013, and acquired this true-color image of a complex cloud pattern over the Azores.

The image captures at least two layers of clouds – one high aloft and one lower - and each layer is being driven by different winds. The lower layer of clouds interacts with the Azores archipelago – a group of nine volcanic islands located about 930 mi (1500 km) west of Lisbon, Portugal. The Azores are some of the tallest mountains on Earth, with Mount Pico, on the island of Pico, rising to 2,351 m (7,713 feet).

Air moving over open ocean flows smoothly, until it encounters an obstacle. When moving air slams against a tall, immobile object, such as an island, the airflow is disrupted. The turbulence created can be written in the clouds. Where the deflected air rises abruptly then falls again, it creates a wave pattern on the lee side of the island, which gradually dissipates. At the top of each wave clouds form, while at the trough, where the air falls and warms, the clouds dissipate, giving rise to a cloud-and-clear pattern.

In addition, sharp, tall obstacles can create motion that expands outward from the point of disturbance, and this appears much like the waves that a ship's sharp bow creates in water while moving forward. In this image, at least two broad rows of such ship-wave-shaped clouds can be seen southwest of the Azores.

A higher layer of thinner, wispy clouds can be seen streaking from west to east across the image, particularly in the central and southern section, blown by winds that move almost perpendicular to the lower level winds. This higher cloud layer appears brighter white, and in some areas obscures the lower-level clouds lying below.

Image Facts
Satellite: Terra
Date Acquired: 5/15/2013
Resolutions: 1km (181.3 KB), 500m (616.7 KB), 250m (1.4 MB)
Bands Used: 1,4,3
Image Credit: Jeff Schmaltz, MODIS Land Rapid Response Team, NASA GSFC