Undulated Shock Surface Formed After a Shock–Discontinuity Interaction

• Published in: Geophysical research letters Vol. 50; no. 10
• Main Authors: Zhou, Yufei, Shen, Chao, Ji, Yong
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 28.05.2023; Wiley
• Subjects: bow shock; Datasets; discontinuities; Discontinuity; Dynamic pressure; Earth; Error analysis; Jets; Magnetic fields; Magnetic reconnection; Magnetopause; Magnetosheath; ripple; Ripples; Shock; Solar wind; space weather; Upstream
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2023GL103848

Shock ripples and shock–discontinuity interactions (SDIs) have long been proposed to explain the frequent occurrence of high‐speed jets (HSJs) in the magnetosheath; however, there is no direct observational evidence for either of them occurring near a shock. Herein, we report a large‐scale, long‐duration undulated quasi‐perpendicular shock surface that is capable of generating HSJs. Based on the curvatures estimated for the shock undulation and for a nearby hot flow anomaly (HFA), we suggest that the shock ripple mechanism and the SDI mechanism combine to generate HSJs, that is, during an SDI, shock undulations and an upstream HFA form simultaneously, and the solar wind between them is deflected by the undulation into jets. The HSJs, discontinuity, and HFA are then convected downstream. An HSJ consistent with our mechanism in another event is presented. Plain Language Summary High‐speed jets are transient structures in the Earth's magnetosheath downstream of the Earth's bow shock. A high‐speed jet can have a dynamic pressure greater than that of the ambient solar wind in the magnetosheath. In some cases, this dynamic pressure can even surpass that of the upstream solar wind. Thus, a high‐speed jet can have a strong impact on the magnetopause, for example, by indenting it over a large spatial scale, exciting eigenmode waves, or triggering a magnetic reconnection. Furthermore, a high‐speed jet can have a significant impact on the geomagnetic environment. It has been independently suggested that shock ripples can explain the origin of high‐speed jets, as can shock–discontinuity interactions. However, despite the wide acceptance of these two mechanisms, there is a lack of direct observational data from near a shock to support either. Using multipoint measurements, we present for the first time evidence that, following its interaction with a solar wind discontinuity, the bow shock becomes deformed/undulated over a large scale for a long duration, which can produce a high‐speed jet. Thus, we suggest that both mechanisms combine to generate high‐speed jets. Key Points We have observed and reconstructed for the first time a three‐dimensional undulated quasi‐perpendicular bow shock surface The undulated shock surface resulted from a shock‐discontinuity interaction The reconstructed saddle‐shaped shock undulation predicts a jet narrow along magnetic field and stretched perpendicular to the field