Search

The tropical arm of Atlantic Multidecadal Variability (AMV) influences climate worldwide, yet the mechanisms generating it remain unclear. Here, we examine experiments with sea surface temperature (SST)‐restoring in the extratropical North Atlantic in multiple models and use mixed‐layer heat budgets to elucidate the important mechanisms. Our results demonstrate that the tropical AMV is driven by wind‐mixed‐layer‐SST feedback. The evolution has two phases with tropical AMV SST anomalies growing from April to October and decaying from November to March. The amplitude of the growth phase surpasses that of the decay phase, resulting in overall tropical Atlantic warming during positive AMV phases. During summer, positive SST anomalies in the extratropics weaken the trade winds, resulting in a shallower mixed‐layer with reduced heat capacity. Subsequent absorption of climatological shortwave radiation in this shallower mixed‐layer then causes SSTs to warm, generating the tropical AMV. Importantly, anomalous surface heat‐fluxes make modest contributions to tropical AMV in these experiments. Plain Language Summary: The North Atlantic sea surface temperature (SST) has fluctuated significantly over periods of decades to multiple decades, a phenomenon known as the Atlantic Multidecadal Variability (AMV). It influences climate worldwide; however, questions remain about how it evolves. This study highlights the vital role of upper ocean processes, particularly the depth of oceanic mixed‐layer, in generating the tropical part of the AMV. Here, we analyzed SST‐restoring climate model experiments in which a surface temperature anomaly is added over the extratropical North Atlantic Ocean. The evolution features a summer growth phase and a winter decay phase, with stronger growth leading to overall warming during positive phases of the tropical AMV. In summer, prevailing trade winds weaken and induce a shallower depth of oceanic mixed‐layer. This leads to the absorption of solar energy in a reduced volume of ocean water, resulting in the warming of SST and the development of a positive phase of tropical AMV. Interestingly, changes in heat‐fluxes over the ocean surface and related mechanisms make little contribution to the development of tropical AMV in these experiments. These results emphasize the importance of accurate upper‐ocean processes for the simulation of AMV in coupled climate models. Key Points: Tropical Atlantic Multidecadal Variability (AMV) is driven by wind‐mixed‐layer‐sea surface temperature (SST) feedback in extratropical SST‐restoring experimentsWeakening of trade winds in summer induces a shallower mixed‐layer, reducing ocean heat capacity and generating positive tropical AMVChanges in surface heat‐fluxes or associated mechanisms are not responsible for tropical AMV in these experiments [ABSTRACT FROM AUTHOR]

An essay is presented which explores the concept of authenticity with regard to art, in response to the arguments presented in Carolyn Korsmeyer's 2019 book "Things: In Touch With the Past." Topics discussed include the difference between an artwork by painter Johannes Vermeer and a forgery of Vermeer by art forger Han van Meegeren in terms of financial and artistic value, the factors being considered in the evaluation of the authenticity in art, the distinction between conventional and conversational implicatures, and the concerns raised about art restorations, copies, and misrepresentation of original sources.