Interplanetary Sheaths and Corotating Interaction Regions: A Comparative Statistical Study on Their Characteristics and Geoeffectiveness

摘要

Interplanetary sheaths and corotating interaction regions (CIRs), while having different solar sources, represent turbulent solar-wind plasma and magnetic field that can perturb the Earth's magnetosphere. We explore long-term solar-wind measurements upstream of the Earth during Solar Cycle 24, from January 2008 to December 2019, to compare their solar-cycle variation, characteristic features, and geoeffectiveness. Earth is found to be encountered by approximate to 2.6 times more CIRs (290) than sheaths (110) during this period. The sheath occurrence follows the F-10.7 solar radio-flux variation, with a cross-correlation coefficient (r(cc)) of +0.71 at zero-year time lag. However, the CIR occurrence is more prominent during the solar cycle descending to minimum phases, reflected in r(cc). values of -0.53 and +0.50 at time lags of -2 and +4 years, respectively, between the CIR occurrence and the F-10.7 solar flux. Both sheath and CIR are characterized by identical average plasma density and interplanetary magnetic-field (IMF) magnitude, and their fluctuations characterized by enhanced variance, and periodic variations of a few minutes to an hour. However, on average, the CIR has approximate to 12% higher plasma speed, approximate to 33% higher temperature, approximate to 20% stronger southward IMF component, approximate to 131% longer duration, and approximate to 158% longer radial extent than the sheath. The intensities of the auroral electrojet index [AEI and the symmetric ring-current index [SYM-H] are, respectively, approximate to 38% and approximate to 55% stronger during the CIR than the sheath, on average. The geoeffectiveness of the CIR is found to be significantly higher than the sheath. Among all CIRs (sheaths), approximate to 25% (approximate to 14%) caused moderate storms (-50 nT >= SYM-H > -100 nT), and approximate to 5% (approximate to 4%) caused intense storms (SYM-H <= -100 nT).