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

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.
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [2] ;  [2] ;  [6]
  1. Univ. of Maryland Baltimore County (UMBC), Baltimore, MD (United States). Joint Center for Earth Systems Technolog; NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States). Earth Science Directorate
  2. NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States). Earth Science Directorate
  3. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). Program for Climate Modeling Diagnosis and Intercomparison
  4. NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States). Earth Science Directorate ; Univ. of Maryland, College Park, MD (United States). Earth System Science Interdisciplinary Center
  5. University of California San Diego, La Jolla, CA (United States). Scripps Institute of Oceanography
  6. NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States). Earth Science Directorate; Universities Space Research Association, Columbia, MD (United States). Goddard Earth Sciences Technology and Research
Publication Date:
Report Number(s):
LLNL-JRNL-736933
Journal ID: ISSN 0094-8276
Grant/Contract Number:
AC52-07NA27344
Type:
Published Article
Journal Name:
Geophysical Research Letters
Additional Journal Information:
Journal Volume: 43; Journal Issue: 3; Journal ID: ISSN 0094-8276
Publisher:
American Geophysical Union
Research Org:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES
OSTI Identifier:
1249953
Alternate Identifier(s):
OSTI ID: 1261227; OSTI ID: 1409978