Magnetotail response to corotating interaction region driven geomagnetic storms: Cluster observations

Abstract. In this work we have selected 40 corotating/stream interaction (CIR) driven geomagnetic storms that occurred between 2001 and 2016, and statistically studied their impacts on the magnetotail. The wavelet transform was applied to the interplanetary magnetic field (IMF) B_z component, magnetotail B_x component, and the auroral electrojet (AE) index during geomagnetic storms. The cross-wavelet technique was applied to determine the periods of higher correlation between the IMF B_z × Tail B_x, IMF B_z × AE index and Tail B_x × AE index. More than 80 % of the most energetic periods in the IMF B_z and magnetotail B_x are found to be shorter than 4 hours, independently of the storm phase. The AE index presented the range between 2–4 hours as the most common with energetic periods for both storm phases. In the recovery phase, periodicities in the AE index are more spread (≤ 12 hours) than for the main phase (≤ 8 hours) probably due to the presence of high-intensity long-duration continuous AE activities (HILDCAAs). From the cross-wavelet analysis (IMF B_z × magnetotail B_x, IMF B_z × AE index and magnetotail B_x × AE index), periods ≤ 4 hours are found to be dominant in both storm phases, which coincide with the cyclic substorm periods. The power spectral analysis showed that the IMF B_z and magnetotail B_x time series follow the Kolmogorov (-5/3) power law. Additionally, the mean values of the spectral indices for the magnetotail B_x and AE index are higher during the recovery phase than the main phase. This suggests that turbulence is more pronounced during the recovery phase of geomagnetic storms driven by CIRs.