Magnetospheric multiscale observations of Earth's oblique bow shock reformation by foreshock ultralow-frequency waves

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.