Amaya, D., M. J. DeFlorio, A. J. Miller and S.-P. Xie, 2017:
WES feedback and the Atlantic Meridional Mode: Observations and CMIP5 comparisons
Climate Dynamics, 49, 1665-1679.
Abstract.
The Atlantic Meridional Mode (AMM) is the dominant
mode of tropical SST/wind coupled variability. Modeling studies have
implicated wind-evaporation-SST (WES) feedback as the primary
driver of the AMM.s evolution across the Atlantic basin; however, a
robust coupling of the SST and winds has not been shown observationally. This study examines
observed AMM growth, propagation, and decay as a
result of WES interactions. Investigation of a lagged
maximum covariance analysis shows that boreal wintertime atmospheric forcing generates positive
SST anomalies (SSTA) through a reduction surface evaporative cooling.
When the AMM peaks in magnitude during spring and summer, upward
latent heat flux anomalies occur over the warmest SSTs and act to
dampen the initial forcing. In contrast, on the southwestward edge
of the SSTA, SST-forced cross-equatorial flow reduces
the strength of the climatological trade winds and provides an anomalous latent heat flux into
the ocean, which causes southwestward propagation of the initial atmosphere-forced SSTA through WES
dynamics. Additionally, the lead-lag relationship of the ocean
and atmosphere indicates a transition from an atmosphere-forcing-ocean
regime in the northern subtropics to a highly coupled regime in
the northern tropics that is not observed in the southern hemisphere. CMIP5 models
poorly simulate the latitudinal transition from a one-way interaction
to a two-way feedback, which may explain why
they struggle to reproduce observed coupled interactions between tropical Atlantic SST and
winds. This analysis provides valuable insight
on how meridional modes act as links between extratropical and tropical
variability and focuses future research aimed at improving climate model simulations.
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