613 Seminar: Tianle Yuan

UMBC-JCET & the Climate & Radiation Laboratory
The North Atlantic sea surface temperature (NASST) can undergo large
fluctuations on multidecadal time scales, commonly known as Atlantic
Multidecadal Oscillation (AMO) or Atlantic Multidecadal Variability.
While the tropical arm of AMO is responsible for many climatic impacts by
AMO, it is often too weak or sometimes absent in current climate models
simulations.  Here we show, using both observational and model evidence,
the role of positive feedbacks from low cloud and desert dust in
generating the tropical arm of AMO.  Estimates of the radiative effects by
the feedbacks are strong enough to largely account for the tropical arm of
AMO with the low cloud positive feedback more dominant. Two feedbacks can
be understood in a consistent dynamic framework in which the response of
tropical surface wind speed to midlatitude SST anomaly is the key.  Most
current models have difficulty in capturing either feedback in the
tropical North Atlantic. The feedbacks provide an amplifying mechanism to
generate the tropical arm of AMO and correctly simulating them may be
critical for a range of studies and applications.