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Positive low cloud and dust feedbacks amplify tropical North Atlantic Multidecadal Oscillation

TitlePositive low cloud and dust feedbacks amplify tropical North Atlantic Multidecadal Oscillation
Publication TypeJournal Article
Year of Publication2016
AuthorsYuan T.L, Oreopoulos L., Zelinka M., Yu H.B, Norris J.R, Chin M, Platnick S., Meyer K.
JournalGeophysical Research Letters
Date Published2016/02
Type of ArticleArticle
ISBN Number0094-8276
Accession NumberWOS:000372056600050
Keywordsafrican dust; AMO; atmospheric response; climate model; climate-change; cloud feedback; coupled dynamics; dust feedback; Meridional overturning circulation; model; ocean; parameterization; sahel rainfall; sst; variability

The Atlantic Multidecadal Oscillation (AMO) is characterized by a horseshoe pattern of sea surface temperature (SST) anomalies and has a wide range of climatic impacts. While the tropical arm of AMO is responsible for many of these impacts, it is either too weak or completely absent in many climate model simulations. Here we show, using both observational and model evidence, that the radiative effect of positive low cloud and dust feedbacks is strong enough to generate the tropical arm of AMO, with the low cloud feedback more dominant. The feedbacks can be understood in a consistent dynamical framework: weakened tropical trade wind speed in response to a warm middle latitude SST anomaly reduces dust loading and low cloud fraction over the tropical Atlantic, which warms the tropical North Atlantic SST. Together they contribute to the appearance of the tropical arm of AMO. Most current climate models miss both the critical wind speed response and two positive feedbacks though realistic simulations of them may be essential for many climatic studies related to the AMO.

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