Kelvin‐Helmholtz wave at the subsolar magnetopause boundary layer under radial IMF

Abstract

AbstractWe present the first observation of the Kelvin‐Helmholtz (KH) rolled‐up vortex at the dayside magnetopause layers under a radial interplanetary magnetic field (IMF). The study uses measurements of four Time History of Events and Macroscale Interactions during Substorms (THEMIS) probes aligned along the YGSE axis about 10 RE upstream of the Earth and located in different regions of the near‐Earth environment. THEMIS C and A serve as monitors of the quiet solar wind and fluctuating magnetosheath conditions, respectively, and THEMIS D and E observe the magnetopause and low‐latitude boundary layer (LLBL) crossings. The analysis shows the following: (1) a radial IMF changes to the southward pointing magnetosheath magnetic field; (2) dayside reconnection forms the thin but dense LLBL; (3) a large velocity shear at the LLBL inner edge excites a train of KH waves; and (4) in spite of a short path from the subsolar point (≈5 RE), one of the KH waves exhibits all features of a fully developed rolled‐up vortex.