Solar wind flow angle and geoeffectiveness of corotating interaction regions: First results

A total of 43 Corotating Interaction Region (CIR)‐induced geomagnetic storms during the unusually deep solar minimum of solar cycle 23 (2006–2010) were identified using a superposed epoch analysis technique. Of these 43 events, detailed cross‐spectrum analyses, between the variations in the Z component of the interplanetary magnetic field (IMF Bz) and the equatorial electrojet (EEJ) strength, were performed for 22 events when the daytime EEJ strengths from Jicamarca were available. The analyses revealed that the ∼30 and ∼60 min periodic components in IMF Bz were causally related to the EEJ strength subject to the average solar wind flow being radial to within 6° at L1 during the interval for which EEJ strengths were considered. This investigation elicits the important role of average solar wind azimuthal flow angle in determining the geoeffectiveness of CIR events. Plain Language Summary Corotating Interaction Regions (CIRs) can disturb the near‐Earth geospace significantly as the charged particles are accelerated in the shocked region in the interplanetary medium due to the passage of CIR and these energetic particles can reach Earth's orbit. Satellites are vulnerable to these high‐energy particles during CIRs. In a technologically developed/developing society, the health of its satellites in the near‐Earth space is crucial. Therefore, determining the geoeffectiveness of CIR is important. Key Points A few periodicities (∼30 and 60 min) in IMF Bz predominantly affect EEJ during CIR events on occasions The geoeffectiveness of CIR events are evaluated in terms of these prompt penetration periodicities in the equatorial ionosphere The CIRs are found to be geoeffective when the average solar wind flow is radial to within 6degrees