In summary, we ﬁ nd possible evidence for a ﬁ eld line resonance in a few B ϕ enhancements seen in the same time frame as the banded ions, with time separations ~40 min, comparable to 0.5 – 1 times the Alfvén bounce period (cf. Figure 10d). However, while the mSWIM model predicts a solar wind dynamic pressure enhance- ment on the following day, which would be within the uncertainty of the modeling, the observations in Figure 11 provide no clear magnetospheric evidence supporting the passage of a global compressional event early on day 123. Nonetheless, because compressional waves propagate in all directions relative to B, compressional perturbations are so spatially dispersed that even a small amplitude compression can have a signi ﬁ cant effect on a global scale. A resonant ﬂ ux tube extracts energy all along its extent from ionosphere to ionosphere and the locally small compressional perturbations can thus be a signi ﬁ cant energy source for the standing wave resonance. So we cannot fully rule out the possibility of a solar wind impulse as the stimu- lus for the FLR.