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

Abstract

Abstract 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:

Yuan, Tianle ^[1]; Oreopoulos, Lazaros ^[2]; Zelinka, Mark ^[3]; Yu, Hongbin ^[4]; Norris, Joel R. ^[5]; Chin, Mian ^[2]; Platnick, Steven ^[2]; Meyer, Kerry ^[6]

---

+ Show Author Affiliations

1. Joint Center for Earth Systems Technology University of Maryland, Baltimore County Catonsville Maryland USA, Earth Science Directorate NASA Goddard Space Flight Center Greenbelt Maryland USA
2. Earth Science Directorate NASA Goddard Space Flight Center Greenbelt Maryland USA
3. Program for Climate Modeling Diagnosis and Intercomparison Lawrence Livermore National Laboratory Livermore California USA
4. Earth Science Directorate NASA Goddard Space Flight Center Greenbelt Maryland USA, Earth System Science Interdisciplinary Center University of Maryland College Park Maryland USA
5. Scripps Institute of Oceanography University of California San Diego La Jolla California USA
6. Earth Science Directorate NASA Goddard Space Flight Center Greenbelt Maryland USA, Goddard Earth Sciences Technology and Research Universities Space Research Association Columbia Maryland USA

Publication Date:

Thu Feb 04 00:00:00 EST 2016

Research Org.:

Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)

Sponsoring Org.:

USDOE Office of Science (SC)

OSTI Identifier:

1249953

Alternate Identifier(s):

OSTI ID: 1261227; OSTI ID: 1409978

Report Number(s):

LLNL-JRNL-736933
Journal ID: ISSN 0094-8276

Grant/Contract Number:  

AC52-07NA27344

Resource Type:

Published Article

Journal Name:

Geophysical Research Letters

Additional Journal Information:

Journal Name: Geophysical Research Letters Journal Volume: 43 Journal Issue: 3; Journal ID: ISSN 0094-8276

Publisher:

American Geophysical Union (AGU)

Country of Publication:

United States

Language:

English

Subject:

58 GEOSCIENCES