مقاله انگلیسی رمزگشایی دینامیک مناطق آب و هوایی در حال تغییر به سمت قطب
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Abstract
Growing evidence indicates that the atmospheric and oceanic circulation experiences a systematic poleward shift in a warming climate. 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. Here, using an idealised coupled aqua-planet model, we explore the mechanism of the shifting circulation, by isolating the contributing factors from the direct CO2 forcing, the indirect ocean surface warming, and the wind-stress feedback from the ocean dynamics. We find that, in contrast to the direct CO2 forcing, ocean surface warming, in particular an enhanced subtropical ocean warming, plays an important role in driving the circulation shift. This enhanced subtropical ocean warming emerges from the background Ekman convergence of surface anomalous heat in the absence of the ocean dynamical change. 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. The shift in wind, in turn drives a shift in the ocean circulation. 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.
Introduction
An increasing amount of evidence suggests that the atmospheric and oceanic circulation is shifting towards the poles under climate change (Thompson et al. 2000; Marshall 2003; Fu et al. 2006; Hu and Fu 2007; Lu et al. 2007; Seidel et al. 2008; Screen et al. 2018). For example, poleward migration of the patterns of storm tracks (Yin 2005), winds (Thompson et al. 2000; Chen et al. 2008), jet streams (Archer and Caldeira 2008), precipitation (Scheff and Frierson 2012), tropical cyclones (Kossin et al. 2014), atmospheric frontal activity (Rudeva and Simmonds 2015), cloud (Norris et al. 2016), atmospheric rivers (Ma et al. 2020) and large-scale ocean circulation (Wu et al. 2012; Yang et al. 2016b, 2020a; Wu et al. 2021) have been identified based on various observations and climate simulations. 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). 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.