On the Importance of the Kelvin‐Helmholtz Instability on Magnetospheric and Solar Wind Dynamics During High Magnetic Shear.

The secondary processes driven by the velocity shear driven Kelvin‐Helmholtz Instability (KHI) in the magnetized plasmas have been shown to be important in producing plasma transport and heating from the shocked solar wind into the Earth's magnetosphere (MSP). The plasma transport into the MSP due to KHI has been shown to be strongest during northward interplanetary magnetic field (IMF) via KHI driven low‐ and mid‐latitude reconnection process. In a recent article, Li et al. (2023), https://doi.org/10.1029/2023gl105539 show Magnetosphere Multi‐Scale (MMS) spacecraft observations of multiple, Alfvénic reconnection jets during southward IMF at the dawn‐side MSP flank. The quasi‐periodic oscillations in plasma parameters and compressed, ion‐scale current sheets were strongly indicative of the MMS crossing regions of MSP‐like and magnetosheath‐like plasma within Kelvin‐Helmholtz waves. In this brief commentary, the importance of this new discovery for magnetospheric and solar wind dynamics is discussed. Plain Language Summary: Earth's magnetic field serves as a protective barrier, forming a magnetic bubble known as the magnetosphere in the solar wind. Acting like a shield, the magnetopause is a crucial surface that delineates the separation between the solar wind and the plasma enveloped within Earth's magnetosphere. However, this shield is not impervious; a phenomenon called magnetic reconnection can compromise it, permitting direct access for solar wind plasma. This process is particularly effective when the interplanetary magnetic field (IMF) carried by the solar wind opposes Earth's magnetic field direction, a configuration known as "southward" IMF. Under these conditions, the Earth's magnetic field opens at the dayside, facilitating the accumulation of mass, momentum, and energy into the night‐side magnetotail. In a recent discovery, NASA's four Magnetosphere Multiscale spacecraft revealed that magnetic reconnection can also occur during southward IMF at the tail flanks of our magnetic bubble. This reconnection, strongly driven by colossal waves with wavelengths of 56,000 km (Kelvin‐Helmholtz waves) creates portals in our magnetic shield, enabling both the escape and entry of particles. In this brief commentary, the importance of this finding is discussed, both for magnetospheric and solar wind dynamics. Key Points: Kelvin‐Helmholtz Instability (KHI) can generate compressed current sheets, effectively driving magnetic reconnection at flanks during southward interplanetary magnetic fieldKHI driven reconnection can aid energetic particle escape from the magnetosphereKHI driven reconnection may also play role for energetic particle dynamics within solar wind structures [ABSTRACT FROM AUTHOR]