SW and Data for Atlantic Niño oscillation

The Atlantic Niño is an important source of the year-to-year variability of the tropical Atlantic, consisting in an irregular oscillation of the Sea Surface Temperature (SST) in the eastern tropical Atlantic. The physical mechanism underlying this oscillation is topic of debate. Some theories, known as dynamical, suggest that the Atlantic Niño is driven by internal wave dynamics. Other theories, termed thermodynamic, propose that the eastern tropical Atlantic SST variability is caused by thermodynamic processes associated with heat fluxes at the ocean surface and/or heat transport by oceanic currents. Here, we examine the SST variability from 1940 to 2022 and find that it can be described in terms of two spatial modes: one in the central and the other in eastern tropical Atlantic. However, focusing on the period from 1993 to 2022, these patterns behave differently. In 1993-2009 they concur in determining the eastern tropical Atlantic SST variability, while in 2010-2022 they act in opposite direction. Therefore, we use Sea Surface Height data and heat fluxes advected by oceanic currents to explore the relative contribution of wave dynamics and heat advection to the eastern tropical Atlantic SST fluctuation. We show that, between 1993 and 2010, the eastern tropical Atlantic SST variability is mainly determined by heat advected from the south by horizontal currents, while between 2010-2022 it can be explained in terms of wave dynamics. This finding suggests that the two spatial patterns determining the eastern tropical Atlantic SST variability, are two distinct physical phenomena forced by different physical mechanisms.

大西洋尼诺（Atlantic Niño）是热带大西洋年际变率的重要驱动源之一，表现为热带东大西洋海表温度（Sea Surface Temperature, SST）的不规则振荡。该振荡的物理机制目前仍存在学术争议。部分被称为动力理论的学说认为，大西洋尼诺由内波动力过程驱动。另有一类被称为热力学理论的学说则提出，热带东大西洋海表温度变率由与海面热通量相关的热力学过程，以及/或洋流所介导的热输送共同导致。本研究分析了1940年至2022年的海表温度变率数据，发现其可通过两个空间模态进行表征：其一对应热带大西洋中部海域，其二对应热带东大西洋海域。但聚焦1993年至2022年这一时间段时，这两个空间模态的表现存在显著差异。在1993年至2009年期间，二者共同作用决定了热带东大西洋海表温度变率；而在2010年至2022年期间，二者的作用方向则完全相反。有鉴于此，本研究采用海面高度（Sea Surface Height）数据与洋流平流输送的热通量，探究了内波动力过程与热平流对热带东大西洋海表温度波动的相对贡献。研究结果显示：1993年至2010年期间，热带东大西洋海表温度变率主要由水平洋流从南部输送而来的热通量所主导；而2010年至2022年期间，其变率则可通过内波动力过程得到合理解释。这一研究结果表明，决定热带东大西洋海表温度变率的两个空间模态实为两种受不同物理机制驱动的独立物理现象。