Whistler-mode chorus waves at Mars

Chorus waves are naturally occurring electromagnetic emissions in space and are known to produce highly energetic electrons in the hazardous radiation belt. The characteristic feature of chorus is its fast frequency chirping, whose mechanism remains a long-standing problem. While many theories agree on its nonlinear nature, they differ on whether or how the background magnetic field inhomogeneity plays a key role. Here, using observations of chorus at Mars and Earth, we report direct evidence showing that the chorus chirping rate is consistently related to the background magnetic field inhomogeneity, despite orders of magnitude difference in a key parameter quantifying the inhomogeneity at the two planets. Our results show an extreme test of a recently proposed chorus generation model and confirm the connection between the chirping rate and magnetic field inhomogeneity, opening the door to controlled plasma wave excitation in the laboratory and space. <br>哨声波（chorus waves）是自然界中存在于太空的电磁辐射，已知其会在具有危害性的辐射带中产生高能电子。哨声波的典型特征为快速频率啁啾，其产生机制长期以来仍是未解的科学难题。尽管诸多理论均认可其非线性本质，但在背景磁场不均匀性是否发挥关键作用、以及如何发挥关键作用这一问题上，各理论尚存分歧。本研究依托火星与地球处的哨声波观测数据，提供了直接证据表明：尽管两颗行星用于量化磁场不均匀性的关键参数存在数个数量级的差异，但哨声波的啁啾速率始终与背景磁场不均匀性存在稳定关联。我们的结果对近期提出的哨声波产生模型进行了极端条件检验，证实了啁啾速率与磁场不均匀性之间的联系，为实验室与太空环境下的可控等离子体波激发研究开辟了新途径。