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

Abstract

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 ≈ 2.6 times more CIRs (290) than sheaths (110) during this period. The sheath occurrence follows the F10.7 solar radio-flux variation, with a cross-correlation coefficient (rcc) 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 rcc values of −0.53 and + 0.50 at time lags of −2 and + 4 years, respectively, between the CIR occurrence and the F10.7 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 ≈ 12% higher plasma speed, ≈ 33% higher temperature, ≈ 20% stronger southward IMF component, ≈ 131% longer duration, and ≈ 158% longer radial extent than the sheath. The intensities of the auroral electrojet index [AE] and the symmetric ring-current index [SYM-H] are, respectively, ≈ 38% and ≈ 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), ≈ 25% (≈ 14%) caused moderate storms (−50 nT ≥ SYM-H > − 100 nT), and ≈ 5% (≈ 4%) caused intense storms (SYM-H ≤ − 100 nT). © 2022, The Author(s), under exclusive licence to Springer Nature B.V.