We announce the detection of a new large jump in the phase of the free core nutation (FCN). This is only the second such large FCN phase jump in more than thirty years of FCN monitoring by means of a very long baseline interferometry (VLBI) technique. The new event was revealed and confirmed by analyzing two FCN models derived from a long-time series of VLBI observations. The jump started in 2021 and is expected to last until the late fall of 2022. The amplitude of the phase jump is expected to be approximately 3 rad, which is as much as 1.5 times larger than the first phase jump in 1999–2000. A connection of the new FCN phase jump with the recent geomagnetic jerk started in 2020 is suggested.

中文翻译：

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新的大自由核心章动阶段跳跃的检测

我们宣布在自由核心章动 (FCN) 阶段检测到新的大跳跃。这仅是 30 多年来通过超长基线干涉测量 (VLBI) 技术进行 FCN 监测的第二次如此大的 FCN 相位跳跃。通过分析源自长期 VLBI 观测序列的两个 FCN 模型，揭示并确认了这一新事件。跳跃始于 2021 年，预计将持续到 2022 年秋末。相位跳跃的幅度预计约为 3 rad，比 1999-2000 年的第一阶段跳跃大 1.5 倍。建议将新的 FCN 相位跳跃与 2020 年开始的最近地磁冲击联系起来。