四维概念模型中大西洋经向环流的规则与混沌Welander振荡
Regular and chaotic Welander oscillations in a four-dimensional conceptual model for the Atlantic Meridional Overturning Circulation
AI总结：
本文通过四维概念模型研究了大西洋经向环流的规则与混沌振荡，揭示了淡水输入对环流强度和混沌行为的影响。
摘要：
大西洋经向环流（AMOC）是地球气候的关键组成部分。证据表明二十世纪出现了减弱，增强的淡水输入到亚极地大西洋可能进一步降低环流强度。我们提出了并研究了一个四维、单半球的箱模型，包含三个部分：热带表面箱、亚极地表面箱和一个大深水箱。输送交换连接表面箱，垂直交换与深海的联系则用平滑的对流调整方案表示。全面的分支分析揭示了一个平衡结构，最多存在四个共存的环流状态，以及双稳态和三稳态的区域。我们识别出一系列周期解和混沌吸引子，具有明显的时间尺度分离：千年振荡受来自亚极地对流突发性关闭的更快的几十年到几百年变化调节。随着规定的淡水通量增加，关闭事件变得更加频繁，背景环流减弱。此外，对于某些淡水输入值，动力学变得混沌，产生不规则的对流开合切换。
英文摘要：
The Atlantic Meridional Overturning Circulation (AMOC) is a key component of the Earth's climate. Evidence indicates a twentieth-century weakening, and enhanced freshwater input to the subpolar North Atlantic may further reduce overturning strength. We present and study a conceptual four-dimensional, single-hemisphere box model with three compartments: a tropical surface box, a subpolar surface box, and a large deep-water box. Advective exchange couples the surface boxes and vertical exchange with the deep ocean is represented by a smooth convective-adjustment scheme. A comprehensive bifurcation analysis reveals an equilibrium structure with up to four coexisting overturning states, together with regimes of bistability and tristability. We identify families of periodic solutions and chaotic attractors with a clear timescale separation: a millennial oscillation is modulated by faster decadal-to-centennial variability arising from episodic shutdowns of subpolar convection. As prescribed freshwater fluxes increase, shutdown events become more frequent and the background overturning weakens. Additionally, for certain values of freshwater influx, the dynamics become chaotic, producing an irregular on-off switching of convection.
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