Positive Low Cloud and Dust Feedbacks Amplify Tropical North Atlantic Multidecadal Oscillation

Area of Science:

• Climatology
• Atmospheric Science
• Oceanography

Background:

• The Atlantic Multidecadal Oscillation (AMO) exhibits a horseshoe pattern of sea surface temperature (SST) anomalies with significant climatic impacts.
• The tropical component of the AMO is crucial for its widespread effects but is inadequately represented in many climate models.

Purpose of the Study:

• To investigate the mechanisms responsible for generating the tropical arm of the AMO.
• To identify the role of low cloud and dust feedbacks in AMO dynamics.

Main Methods:

• Analysis of observational data and climate model simulations.
• Examination of sea surface temperature (SST) anomalies and atmospheric dynamics.

Main Results:

• Positive low cloud and dust feedbacks, particularly low cloud feedback, are sufficient to generate the tropical arm of the AMO.
• Weakened tropical trade wind speeds, in response to mid-latitude SST anomalies, reduce dust and low cloud cover, warming the tropical North Atlantic.
• This dynamical framework explains the appearance of the tropical AMO arm.

Conclusions:

• The study highlights the critical role of wind-driven cloud and dust feedbacks in AMO formation.
• Current climate models often fail to capture the necessary wind speed response and positive feedbacks, limiting their accuracy in AMO-related research.