Cross-correlation and cross-wavelet analyses of the solar wind IMF Bz and auroral electrojet index AE coupling during HILDCAAs

Abstract

Solar-wind-geomagnetic activity coupling during high-intensity long-duration continuous AE (auroral electrojet) activities (HILDCAAs) is investigated in this work. The 1-min AE index and the interplanetary magnetic field (IMF) Bz component in the geocentric solar magnetospheric (GSM) coordinate system were used in this study. We have considered HILDCAA events occurring between 1995 and 2011. Cross-wavelet and cross-correlation analyses results show that the coupling between the solar wind and the magnetosphere during HILDCAAs occurs mainly in the period ≤ 8h. These periods are similar to the periods observed in the interplanetary Alfvén waves embedded in the high-speed solar wind streams (HSSs). This result is consistent with the fact that most of the HILDCAA events under present study are related to HSSs. Furthermore, the classical correlation analysis indicates that the correlation between IMF Bz and AE may be classified as moderate (0.4-0.7) and that more than 80% of the HILDCAAs exhibit a lag of 20-30min between IMF Bz and AE. This result corroborates with Tsurutani et al. (1990) where the lag was found to be close to 20-25min. These results enable us to conclude that the main mechanism for solar-wind-magnetosphere coupling during HILDCAAs is the magnetic reconnection between the fluctuating, negative component of IMF Bz and Earth's magnetopause fields at periods lower than 8h and with a lag of about 20-30min.