NASA MODIS Image of the Day: February 25, 2013 - Ship-wave-shape wave clouds induced by Iceberg A62, South Atlantic Ocean

Status Report From: NASA MODIS Web
Posted: Monday, February 25, 2013

In mid-February, 2013 the Terra satellite passed over the remote South Atlantic Ocean and captured an intriguing image illustrating the effect of a large iceberg on cloud formation. The Moderate Resolution Imaging Spectroradiometer (MODIS) aboard that satellite captured this true-color image at 1150 UTC (6:50 a.m. EST) on February 13. In this image, the large Iceberg A62 floats on the dark water, and is covered by a thin layer of cloud. It is the extremely high reflectivity of the dense ice which allows the bright white iceberg to be seen through the duller white of the cloud layer. A steady wind appears to be blowing from the west towards the east, causing a brush-stroke like texture in the clouds around and over Iceberg A62. On the leeward (east) side of the iceberg, a pattern of dark and light clouds appears. This pattern looks much like the waves created as a ship powers through water. These ship- wave-shaped wave clouds, however, are not caused by the movement of water, but by the movement of air. As rapidly moving air hits against the tall iceberg, the smooth forward motion comes to an abrupt halt, sending air over and around the icy obstacle. A wave of disturbed air forms, and it rises and falls in marked intervals on the leeward side, causing peaks and troughs in the air flow. Rising air cools and, because the air is moist, clouds form at the peaks. As the air falls, it warms and the clouds dissipate. The formation and dissipation of clouds in the rising and falling air creates the striking wave-like pattern.

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