Equator-S observation of reconnection coupled to surface waves Original Research Article

In the morning sector of its near equatorial orbit Equator-S observed large magnetic oscillations in the Pc 5 frequency range. The poloidal part of the observed oscillations is usually interpreted as being caused by surface waves of the magnetopause driven by a Kelvin-Helmholtz instability (KHI). We found, however, that these oscillations are sometimes additionally superposed with reconnection signatures. This occurs during periods of northward interplanetary magnetic field. In fact, the Walen relation as a test for reconnection is satisfied for many short periods of time. This indicates transient and thin layers of reconnection, embedded in the large scale motion. We compared our observations with appropriate magnetohydrodynamic simulations allowing reconnection in the case of shear flows. Comparing the simulation results with the magnetic field and plasma observations we found good agreement of simulations and observations. We conclude that Equator-S has observed reconnection embedded in Kelvin-Helmholtz instability generated vortices in its nonlinear phase.