Journal Article

Dawn‐Dusk Asymmetry of Kelvin‐Helmholtz Vortices Along the Kronian Magnetopause

Zhang, Binzheng, Delamere, Peter A., Feng, Enhao, Yao, Zhonghua, Zheng, Zhiqi

2025

Overview

The Kelvin‐Helmholtz instability (KHI) at the Kronian magnetopause is an important process resulting from the interaction between the magnetosphere and the solar wind. The Kronian magnetosphere is rotationally driven, thus dawn‐dusk asymmetry has been observed in the KHI structures. However, analyses based on the Cassini data have yielded a discrepancy, with some studies indicating more KHI features on the duskside and others on the dawnside. To investigate the physical origin of the dawn‐dusk asymmetry of the Kronian KHI, three‐dimensional high‐resolution global simulations of the Kronian magnetosphere have been developed. We found that KHI structures continuously develop in the prenoon sector and propagate toward both the dawn and dusk sides, exhibiting clear dawn‐dusk asymmetry during their growth and propagation. Our study reveals the dawn‐dusk asymmetric characteristics of KHI along Kronian magnetopause, including its growth and propagation, providing important insights into the interaction between rotation‐driven magnetosphere and solar wind. Plain Language Summary The Kelvin‐Helmholtz instability (KHI) vortex at Saturn's magnetopause, driven by the interaction between Saturn's magnetosphere and the solar wind, represent a significant process. Observational evidence confirms the existence of these KHI structures at Saturn's magnetopause. With rapid rotation, Saturn is expected to exhibit dawn‐dusk asymmetry in KHI characteristics or spatial distribution. Statistical analyses of Cassini mission data have yielded conflicting results, with some studies indicating more KHI features, such as bipolar signatures in the magnetic field data, on the duskside and others on the dawnside. To investigate the dawn‐dusk asymmetry of Saturn's KHI, we conducted global three‐dimensional magnetohydrodynamic simulations of Saturn's magnetosphere. We found that KHI structures continuously develop in the prenoon sector of Saturn's magnetosphere and propagate toward both the dawn and dusk sides, exhibiting clear dawn‐dusk asymmetry in their growth and propagation. At a fixed eigenfrequency, KHI structures propagate more stably toward the duskside with higher eigenfrequencies. Conversely, on the dawnside, KHI structures exhibit lower eigenfrequencies and unstable growth and propagation due to the presence of more complex physical processes. Our work elucidates the characteristics of KHI at Saturn's magnetopause, which is important for understanding the interaction between rotation‐driven planetary magnetosphere and solar wind. Key Points In the global MHD model, Kelvin‐Helmholtz vortices start to form near the noon sector and propagate toward the dawn and dusk directions The Kelvin‐Helmholtz Instabilities along the Kronian magnetopause shows low frequency, high amplitude on dawnside, opposite on duskside The Kelvin‐Helmholtz vortices are comparatively stable during propagation toward the duskside, but are less stable on the dawnside

• Publisher: John Wiley & Sons, Inc
• Subject: Asymmetry / Kelvin-helmholtz instability / magnetohydrodynamic simulation / Magnetopause / Magnetospheres / Magnetospheric-solar wind relationships / Saturn's magnetosphere / Solar wind