The interaction between waves and particles is crucial for particle acceleration near interplanetary shocks. Previously, research on these processes was constrained by limited data and the coarse time resolution of interplanetary missions. However, recent high-resolution observations from the Solar Orbiter mission are providing new insights into this area. We analyzed data measured by the Energetic Particle Detector, the Magnetometer, and the Solar Wind Analyzer on board Solar Orbiter, to investigate wave-proton interactions upstream an interplanetary shock observed on April 8, 2022. We performed a mean-field-transformed wavelet analysis on the magnetic field data to derive the wave properties. We reconstructed pitch angle distributions and gyrophase distributions in the solar wind frame of reference to analyze the proton behavior. We find that the observed waves are quasi-parallel propagating, ion-scale transverse waves that exhibit alternating left-handed and right-handed polarization. Fluxes of suprathermal protons oscillate quasi-periodically with these waves and show signs of wave modulation. In addition, signatures hinting at resonance, such as phase shifts across energy, are revealed in proton fluxes. The proton phase space density near the calculated resonant energy increases during the interaction, which indicates the acceleration or scattering of protons. We present direct observations of particles resonating with waves close to an interplanetary shock, which captures these dynamics within single wave periods. Our results highlight the role of wave-particle interactions in dynamic processes occurring in the inner heliosphere.

Xing-Yu Li

Liu Yang

Verena Heidrich-Meisner

Robert F. Wimmer-Schweingruber

Qiu-Gang Zong

Linghua Wang

Lars Berger

Erik Jentsch

Duncan Keilbach

Maximilian Hecht

Javier Rodríguez-Pacheco

Astronomy and Astrophysics

ASTRONOMY & ASTROPHYSICS 是一本国际期刊，独立于用于获得结果的技术发表关于天文学和天体物理学（理论、观测和仪器）各个方面的论文。

Astronomy and Astrophysics is an international journal that focuses on various aspects of astronomy and astrophysics, including theory, observation, and instrumentation. The journal publishes high-quality academic papers independently of the techniques used to obtain research results.

《Astronomy and Astrophysics》是一本国际性期刊，专注于天文学和天体物理学的各个方面，包括理论、观测和仪器技术。该期刊独立于用于获得研究结果的技术，发表高质量的学术论文。

Category	Quartile
物理与天体物理	2
物理与天体物理, 天文与天体物理	2

Resonant interactions between suprathermal protons and ion-scale waves near an interplanetary shock

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