The near-Earth space serves as the most accessible laboratory for studying the interaction between a star and a magnetized planet, providing insights into various heliospheric and astrophysical systems throughout the universe. Two key physical processes that govern the Sun-Earth interaction are magnetic reconnection (RX) and the Kelvin-Helmholtz instability (KHI). The former is triggered by a large magnetic-field shear, while the latter is powered by a large flow-velocity shear. Both processes exhibit a multi-scale nature, ranging from electron scale and ion scale to the global and magnetohydrodynamic (MHD) scales. Recent studies have revealed that KHI can facilitate the onset of RX and vice versa. This highlights the close linkage between KHI and RX, the effects of which can propagate to the entire global system. For example, Kelvin-Helmholtz waves/vortices (KHWs/KHVs) at the flank magnetopause can affect the stability of the central plasma sheet, triggering the onset of magnetotail RX. KHWs can act as conduits not only for solar wind entry but also for the escape of energetic particles from Earth. Additionally, KHVs contribute to the magnetosphere-ionosphere coupling via field-aligned currents and the dawn-dusk asymmetry. This presentation will focus on the multi-scale characteristics of KHI and diverse pathways driven by KHWs/KHVs in the Sun-Earth interaction that remain elusive. It will conclude by proposing a mission concept aimed at addressing these long-lasting and unexplored areas in heliophysics research.

recording: www.youtube.com/watch