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

摘要

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 (approximate to 33 year(-1)), followed by occurrences during solar minimum (approximate to 24 year-1), the ascending phase (approximate to 22 year-1), and solar maximum (approximate to 11 year-1). At 1 AU, CIRs are found to be large-scale interplanetary structures with an average (median) duration of approximate to 26 hours (approximate to 24 hours) and radial extent of approximate to 0.31 AU (approximate to 0.27 AU). CIRs are characterized by average (median) plasma density of approximate to 29 cm(-3) (approximate to 26 cm(-3)), ram pressure of approximate to 11 nPa (approximate to 9 nPa), temperature of approximate to 5 x 10(5) K (approximate to 4x10(5) K), and magnetic-field magnitude of approximate to 15 nT (approximate to 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 = 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).