![]() And those SST variations were interpreted as a feature of fluctuations of the Pacific Decadal Oscillation, which is one of the internal climate variabilities. ![]() However, observations imply that the spatial and temporal evolution of SST play a dominant role in driving the recent tropical expansion (Allen and Kovilakam 2017 Grise et al. Some of these simulations are even without involving changes in the ocean. 2012) or by introducing uniform sea surface temperature (SST) warming (Chen et al. Climate model simulations can reproduce the tropical expansion by changing the atmospheric concentration of greenhouse gases (Lu et al. Early studies have been mainly focused on the atmospheric processes in driving the shift in the atmospheric circulation, concentrating on a specific topic named tropical expansion (Fu et al. In the past decades, numerous investigations have been carried out to decode the mechanisms (Staten et al. Understanding the underlying causes does not only help us to understand why it happens, but also serve to better predict and boost our confidence in the global warming induced climate changes. These climate pattern shifts redistribute the natural resources, such as water, vegetation and the related ecosystems, thus having broad implications for our societies (Heffernan 2016). 2021) have been identified based on various observations and climate simulations. 2020) and large-scale ocean circulation (Wu et al. 2014), atmospheric frontal activity (Rudeva and Simmonds 2015), cloud (Norris et al. 2008), jet streams (Archer and Caldeira 2008), precipitation (Scheff and Frierson 2012), tropical cyclones (Kossin et al. For example, poleward migration of the patterns of storm tracks (Yin 2005), winds (Thompson et al. Our simulations, despite being idealised, capture the main features of the observed climate changes, for example, the enhanced subtropical ocean warming, poleward shift of the patterns of near-surface wind, sea level pressure, storm tracks, precipitation and large-scale ocean circulation, implying that increase in greenhouse gas concentrations not only raises the temperature, but can also systematically shift the climate zones poleward.Īn increasing amount of evidence suggests that the atmospheric and oceanic circulation is shifting towards the poles under climate change (Thompson et al. The shift in wind, in turn drives a shift in the ocean circulation. It expands the tropical warm water zone, causes a poleward shift of the mid-latitude temperature gradient, hence forces a corresponding shift in the atmospheric circulation and the associated wind pattern. This enhanced subtropical ocean warming emerges from the background Ekman convergence of surface anomalous heat in the absence of the ocean dynamical change. We find that, in contrast to the direct CO \(_2\) forcing, ocean surface warming, in particular an enhanced subtropical ocean warming, plays an important role in driving the circulation shift. Here, using an idealised coupled aqua-planet model, we explore the mechanism of the shifting circulation, by isolating the contributing factors from the direct CO \(_2\) forcing, the indirect ocean surface warming, and the wind-stress feedback from the ocean dynamics. However, the complexity of the climate system, including the coupling between the ocean and the atmosphere, natural climate variability and land-sea distribution, tends to obfuscate the causal mechanism underlying the circulation shift. Growing evidence indicates that the atmospheric and oceanic circulation experiences a systematic poleward shift in a warming climate. ![]()
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