Inward Radial Decay of Magnetopause Perturbations

Abstract Theory predicts that the magnetic field strength perturbations produced by the Kelvin‐Helmholtz instability decay exponentially with distance inward from the magnetopause but that the perturbations generated by isolated cylindrical indentations on the magnetopause (e.g., flux transfer events or FTEs) decay as the inverse square of the distance from the magnetopause. By contrast, global magnetohydrodynamic simulations indicate that planar density fronts in the solar wind produce perturbation amplitudes that initially decay with inward radial distance from the magnetopause but then increase with further distance inward due to the superposition of incident and reflected fast mode compressional waves. Time History of Events and Macroscale Interactions during Substorms A–E magnetic field strength observations from 0000 to 0500 UT on 31 July 2007 within the subsolar magnetosphere confirm the inward propagation of perturbations whose peak amplitude and standard deviation decay rapidly with distance from the magnetopause. Solar wind, magnetosheath, and magnetospheric observations suggest an interpretation of the perturbations in terms of boundary ripples driven by solar wind pressure perturbations.