Kelvin‐Helmholtz Waves and Magnetic Reconnection at the Earth's Magnetopause Under Southward Interplanetary Magnetic Field

Abstract

Abstract We present Magnetospheric Multiscale (MMS) observations of a K‐H wave event under southward IMF conditions, accompanied by ongoing magnetic reconnection. The nonlinear K‐H waves are characterized by quasi‐periodic fluctuations, the presence of low‐density and high‐speed ions, and variations in the boundary normal vectors at both the leading and trailing edges. Our observations reveal clear evidence of on‐going magnetic reconnection through the identification of Alfvénic ion jets and the escape of energetic magnetospheric electrons. Among the 36 magnetopause current‐sheet crossings in this event, 19 exhibit unambiguous signatures of reconnection at both the leading (7) and trailing (12) edges. Notably, the estimated current‐sheet thicknesses at both edges are comparable to the ion‐inertial scale, confirming the compression effect resulting from the large‐scale evolution of the K‐H waves. The reconnection jets potentially contribute to the suppression of K‐H growth through boundary‐layer broadening and the development of complex flow and magnetic field patterns.