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Abrupt cloud clearing of marine stratocumulus in the subtropical southeast Atlantic

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Science  17 Aug 2018:
Vol. 361, Issue 6403, pp. 697-701
DOI: 10.1126/science.aar5836

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A shrinking marine refrigerator

Low subtropical marine clouds scatter solar radiation back to space and thereby cool the climate system. Most work on understanding changes in the coverage of these types of clouds has focused on the effects of sea surface temperatures or on aerosols. Yuter et al. show that dynamic effects due to atmospheric gravity waves are responsible for the rapid clearing of large areas of these clouds. This phenomenon also has implications for marine ecology and biogeochemistry.

Science, this issue p. 697

Abstract

We document rapid and abrupt clearings of large portions of the subtropical marine low cloud deck that have implications for the global radiation balance and climate sensitivity. Over the southeast Atlantic, large areas of stratocumulus are quickly eroded, yielding partial or complete clearing along sharp transitions hundreds to thousands of kilometers in length that move westward at 8 to 12 meters per second and travel as far as 1000+ kilometers from the African coast. The westward-moving cloudiness reductions have an annual peak in occurrence in the period from April through June. The cloud erosion boundaries reduce cloud at ≈10-kilometer scale in less than 15 minutes, move approximately perpendicular to the mean flow, and are often accompanied by small-scale wave features. Observations suggest that the cloud erosion is caused by atmospheric gravity waves.

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