[P-EM16] Heliosphere and Interplanetary Space

[PEM16-P04] Statistical analysis of upstream waves observed by KPLO and ARTEMIS in the solar wind

*Junhyun Lee¹, Khan-Hyuk Kim², Ensang Lee², Ho Jin², Seul-Min Baek¹, Minsup Jeong¹, Young-Jun Choi¹, Chae Kyung Sim^1,3 (1.Korea Astronomy and Space Science Institute, 2.Kyung Hee University, 3.Korea National University of Science and Technology)

Keywords:upstream wave, cross-phase analysis, high-coherence wave

is well known that ions traveling upstream from Earth’s bow shock into the incoming solar wind generate upstream ultralow frequency (ULF) waves, ranging from 0.01 to 0.1 Hz. In this study, we conduct a statistical analysis of the propagation characteristics of upstream waves using cross-phase analysis of magnetic field data obtained from KPLO and THEMIS-ARTEMIS in the upstream region over a two-year period, from January 2023 to December 2024. Wave properties are investigated in both the spacecraft and solar wind reference frames. The KPLO and ARTEMIS measured upstream ULF waves with a small separation (<1 R_E) in the upstream region. For the cross-phase analysis, we identified high-coherence wave events (> 0.6) lasting over 10 minutes in the combined KPLO-ARTEMIS data. The cross-phase analysis provides the time delay of upstream waves observed at KPLO and ARTEMIS. Consequently, the wave propagation velocity between the two observation points can be determined in the spacecraft reference frame. By considering wave propagation in the solar wind, we found that upstream waves propagate with nearly zero phase velocity in the solar wind reference frame. This indicates that the observed waves are convected past the spacecraft by the solar wind without propagating into the upstream region. We discuss how and where these waves are generated.