Magnetic Structure and Electromagnetic Waves at a Northward IMF Merging Site

On March 18, 2002, the Cluster satellites traveled from the earths northern mantle into the magnetosheath. During this time, the IMAGE spacecraft observed a long-lived proton emission northward of the auroral zone. First we present Cluster electron, ion and magnetic field evidence for an encounter with this active merging site at the magnetopause. Simulations predict that Cluster lies near a local three-dimensional separator line. We therefore present our model as a two-dimensional projection of a three-dimensional merging geometry. Then we discuss magnetic and electric field waves encountered near the site, and develop a functional fit to the wave fields by way of their polarization, frequency spectrum, and direction of propagation. We observe nearly monochromatic, low frequency, circularly and linearly polarized waves on either side of the x-line. We explore their role in the merging process and what they reveal about the structure and motion of the merging site.