Whistler-mode waves upstream of planetary bow shock are often referred to as “1-Hz waves” due to the center of their observed frequency range being at ∼1 Hz. A series of whistler-mode waves were observed upstream of the Martian bow shock by MAVEN on 2015 August 14, with unusually low frequencies centered at ∼0.4 Hz. These waves were accompanied (though not synchronized) by the significant flux enhancement of high-energy protons up to ∼10 keV. By analyzing the wave dispersion property and the wave–particle interaction condition, we find that the observed whistler-mode waves have the potential of resonating with protons of ∼1 keV with large pitch angles up to nearly perpendicular to the background magnetic field, thereby providing a feasible means of accounting for proton acceleration. Our results indicate the possible origin of energized protons in the Martian environment through the interaction with whistler-mode waves, and their potential relationship with the unique upstream conditions.

中文翻译：

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异常低频哨声模式波及其与火星弓激波上游观测到的高能质子的关联

行星弓激波上游的惠斯勒模式波通常被称为“1赫兹波”，因为它们观测到的频率范围的中心位于~1赫兹。 2015 年 8 月 14 日，MAVEN 在火星弓形激波上游观测到一系列哨声波，其频率异常低，中心频率为 ∼0.4 Hz。这些波伴随着（尽管不同步）高达~10 keV的高能质子通量的显着增强。通过分析波的色散特性和波粒相互作用条件，我们发现观测到的哨声模式波具有与约1 keV的质子共振的潜力，其大俯仰角几乎垂直于背景磁场，从而提供解释质子加速的可行方法。我们的结果表明，火星环境中高能质子可能通过与哨声波相互作用而起源，以及它们与独特的上游条件的潜在关系。