The North Atlantic Oscillation (NAO) is a dominant atmospheric variability in the Northern Hemisphere that has a substantial impact on weather and climate on various time scales. Here, we investigate the role of energy conversion terms day-by-day during the NAO life cycle. The relative timing and contribution of the energy conversion terms are quantified by projecting the terms onto the eddy total energy, eddy kinetic energy (EKE), and eddy available potential energy (EAPE) patterns associated with the NAO. The results show a remarkable phase dependence in the growth and maintenance mechanisms. For positive NAOs, the initial growth is driven by the barotropic interactions between the eddies propagating over North America. This suggests that a non-local growth mechanism plays an important role in the initiation of positive NAOs. In contrast, it is the baroclinic processes that initiate negative NAOs. The conversion of the mean APE into the EAPE and then into the EKE, processes which include eddy heat fluxes and vertical motions, results in the relatively local growth of negative NAOs. During the mature phase, the largest source of energy is the conversion of the mean APE into EAPE. Part of this is converted to EKE, making a substantial contribution to the maintenance of the EKE. This process is particularly important for negative NAOs.

中文翻译：

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北大西洋涛动日常能量学中增长机制的相位依赖性

北大西洋涛动（NAO）是北半球的主要大气变化，对不同时间尺度的天气和气候产生重大影响。在这里，我们研究了 NAO 生命周期中能量转换术语的日常作用。通过将能量转换项投影到与 NAO 相关的涡流总能量、涡流动能 (EKE) 和涡流可用势能 (EAPE) 模式上来量化能量转换项的相对时间和贡献。结果显示生长和维持机制具有显着的相依赖性。对于正 NAO，最初的增长是由北美上空传播的涡流之间的正压相互作用驱动的。这表明非局部增长机制在积极 NAO 的启动中发挥着重要作用。相反，正是斜压过程引发了负 NAO。将平均 APE 转换为 EAPE，然后转换为 EKE，这一过程包括涡流热通量和垂直运动，导致负 NAO 相对局部生长。在成熟阶段，最大的能量来源是平均APE转化为EAPE。其中一部分转换为EKE，为EKE的维护做出了巨大贡献。这个过程对于消极的 NAO 尤为重要。