Time-dependent evolution of externally driven MHD/EMIC waves in the low-latitude magnetosphere

Abstract:

The magnetosphere is often perturbed by external sources, which may excite various low frequency waves. The excitation of such waves inside the magnetosphere should depend on the characteristics of sources as well as the profile of an inhomogeneous magnetosphere. Since many observations are limited to the local measurements in space, it becomes important to understand how the magnetosphere responds to a certain external source at the different locations in space. In this study, we investigate how MHD and EMIC waves are excited preferentially by the different external sources and they appear at the different positions, and how their E and B time histories are affected by either impulsive sources or long lasting sources, respectively. We adopt the theoretical technique called the IIM (invariant imbedding method) in a simplified model that allows arbitrary inhomogeneity, but exact calculations on the wave coupling problem, and also the numerical dipole models for MHD/EMIC wave simulation studies, respectively. It is found that the initial time-dependent responses at the various locations become sensitive to the time-scale of the impulsive sources. In addition, we present how MHD waves are affected by the continuous movement of the magnetosphere and how EMIC waves are affected by the co-existing MHD waves. Each case is accompanied by numerical simulation studies, which are found to be consistent with the theoretical results.