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The By-component of the interplanetary magnetic field (IMF) has consistently been shown to exert significant influence on the variability of the coupled solar wind-magnetosphere-ionosphere system. Through multiple superposed epoch analyses, we have identified some of the timings involved in the SW-M-I system’s response to reversals in the orientation of IMF By component. Data from the Cluster Electron Drift Instrument indicates that the lobes respond quickly, with initial changes starting in as a little as 5 min after a reversal and an end state being reached within 30-40 min. Data from the ground-based SuperDARN radar network show that ionospheric flows also respond on these prompt timescales. However, plasma flows recorded in the plasmasheet, including an analysis of fast flow events, shows that this region is much more complex with significant variation in its response to IMF By reversals – perhaps due to the effect of local small-scale processes.