Small-scale, localized electromagnetic waves observed by Cluster: Result of magnetosphere-ionosphere interactions

We present results from a numerical study of small‐scale, localized electromagnetic structures measured by the Cluster satellites on May 19, 2002, in the nightside magnetosphere. A comprehensive analysis of these structures by Karlsson et al. (2004), Johansson et al. (2004) and Marklund et al. (2004) demonstrates that they can be interpreted as two relatively stationary magnetic field‐aligned currents and higher frequency shear Alfvén waves, populating the region in between, but no explanation was given of what physical mechanism may cause such particular combination of waves and currents in the plasma sheet boundary layer. Our simulations demonstrate that these structures can be interpreted as a characteristic signature of the active ionospheric feedback, which appears when large‐scale magnetic field‐aligned currents interact with the ionosphere.