The magnetosheath region is confined between the terrestrial bow shock and the magnetopause. The magnetosheath is a very turbulent region filled with high amplitude waves and nonlinear structures. Magnetic holes or magnetic dips are among the most commonly observed structures there. For the past few decades, the dominant view has been that these structures are non-propagating mirror waves carried by the solar wind flow.
Yao et al.  exploited high resolution Magnetospheric MultiScale (MMS) data to perform a comprehensive analysis of magnetic dip structures within the magnetosheath. They present observations of various types of magnetic dips, categorized as “frozen‐in,” “expanding,” “contracting,” and “stable‐propagating.”
The observation of the “stable‐propagating” magnetic dip structure with a sunward component of the propagation direction is a very significant result. This study has shown that not only the upstream boundary (the shock) but also the downstream boundary (the magnetopause) can be associated with the sources of magnetic dips.
Citation: Yao, S. T., Hamrin, M., Shi, Q. Q., Yao, Z. H., Degeling, A. W., Zong, Q.‐G., et al. . Propagating and dynamic properties of magnetic dips in the dayside magnetosheath: MMS observations. Journal of Geophysical Research: Space Physics, 125, e2019JA026736. https://doi.org/10.1029/2019JA026736
—Michael Balikhin, Editor in Chief, JGR: Space Physics