Corotating Interaction Regions during Solar Cycle 24: A Study on Characteristics and Geoeffectiveness

Abstract

Corotating interaction regions (CIRs) form in the interaction region between the solar-wind high-speed streams and slow streams, leading to compressed plasma and magnetic fields. Using solar-wind measurements upstream of Earth, we identified 290 CIRs encountered by Earth during January 2008 through December 2019 (Solar Cycle 24). The occurrence rate is the maximum during the solar-cycle descending phase (≈ 33 year−1), followed by occurrences during solar minimum (≈ 24 year−1), the ascending phase (≈ 22 year−1), and solar maximum (≈ 11 year−1). At 1 AU, CIRs are found to be large-scale interplanetary structures with an average (median) duration of ≈ 26 hours (≈ 24 hours) and radial extent of ≈ 0.31 AU (≈ 0.27 AU). CIRs are characterized by average (median) plasma density of ≈ 29 cm−3 (≈ 26 cm−3), ram pressure of ≈ 11 nPa (≈ 9 nPa), temperature of ≈ 5 × 10 5 K (≈ 4 × 10 5 K), and magnetic-field magnitude of ≈ 15 nT (≈ 14 nT). The CIR characteristic features exhibit no clear solar-cycle phase dependence. About 30% of the CIRs are found to be geoeffective, causing geomagnetic storms with the peak SYM-H ≤ − 50 nT; 25% caused moderate storms (−50 nT ≥ SYM-H > − 100 nT), and 5% caused intense storms (SYM-H ≤ − 100 nT). The geoeffectiveness is found to decrease with the decreasing solar flux. CIRs during equinoxes are found to be more geoeffective compared to those during solstices. On average, SYM-H is strongly associated with the CIR plasma characteristic parameters (anti-correlation coefficient r= − 0.65 to −0.89), while the association is weaker for the AE-index (r= 0.41 to 0.67). © 2022, The Author(s), under exclusive licence to Springer Nature B.V.