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Magnetospheric Multiscale Observations of Earth's Oblique Bow Shock Reformation by Foreshock Ultralow‐Frequency Waves
Author(s) -
Liu Terry Z.,
Hao Yufei,
Wilson Lynn B.,
Turner Drew L.,
Zhang Hui
Publication year - 2021
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2020gl091184
Subject(s) - foreshock , bow shock (aerodynamics) , bow wave , magnetosheath , physics , geophysics , shock (circulatory) , oblique shock , shock wave , oblique case , solar wind , seismology , geology , mechanics , aftershock , magnetic field , magnetopause , medicine , linguistics , philosophy , quantum mechanics
Collisionless shocks can be nonstationary with periodic reformation shown in many simulation results, but direct observations are still tenuous and difficult to conclusively interpret. In this study, using Magnetospheric Multiscale (MMS) observations, we report direct observational evidence of Earth's oblique bow shock reformation driven by the foreshock Ultralow‐Frequency (ULF) waves. When the four MMS spacecraft were in a string‐of‐pearls formation roughly along the bow shock normal, they observed that when each period of foreshock ULF waves encountered the bow shock, a new shock ramp formed. Meanwhile, in the magnetosheath, the old bow shock's remnants were observed periodically convecting downstream. We propose that the reformation mechanism of the oblique bow shock is the variation of the upstream conditions by the periodic ULF waves as they encounter the bow shock. We also examine the nature of reflected ions during the reformation process.