Energy circulation in geospace lies at the heart of space weather research. In the inner magnetosphere, the steep plasmapause boundary separates the cold dense plasmasphere, which corotates with the planet, from the hot ring current/plasma sheet outside. Theoretical studies suggested that plasmapause surface waves related to the sharp inhomogeneity exist and act as a source of geomagnetic pulsations, but direct evidence of the waves and their role in magnetospheric dynamics have not yet been detected. Here, we show direct observations of a plasmapause surface wave and its impacts during a geomagnetic storm using multi-satellite and ground-based measurements. The wave oscillates the plasmapause in the afternoon-dusk sector, triggers sawtooth auroral displays, and drives outward-propagating ultra-low frequency waves. We also show that the surface-wave-driven sawtooth auroras occurred in more than 90% of geomagnetic storms during 2014–2018, indicating that they are a systematic and crucial process in driving space energy dissipation.

地球空间的能量循环是空间天气研究的核心。在内磁层中，陡峭的等离子体层顶边界将与行星同步旋转的冷致密等离子体层与外部的热环电流/等离子体层分开。理论研究表明，与急剧不均匀性相关的等离子体层顶表面波存在，并且是地磁脉动的来源，但尚未检测到这些波及其在磁层动力学中的作用的直接证据。在这里，我们展示了使用多卫星和地面测量对等离子层顶表面波及其在地磁风暴期间的影响的直接观测。该波使午后黄昏区域的等离子层顶振荡，触发锯齿状极光显示，并驱动向外传播的超低频波。我们还发现，2014-2018年期间，90%以上的地磁暴都出现了表面波驱动的锯齿极光，这表明它们是驱动空间能量耗散的系统且关键的过程。