Solar cycle evolution of ICME sheath regions at 1 AU

TL;DR

This study analyzes how ICME sheath regions at 1 AU evolve across solar cycles 23 to 25, revealing cycle-dependent changes in pressure, turbulence, magnetic complexity, and flow patterns, emphasizing the influence of upstream solar wind conditions.

Contribution

It provides the first comprehensive statistical analysis of ICME sheath evolution over multiple solar cycles, highlighting the impact of solar cycle phase on sheath properties and turbulence.

Findings

Sheath total pressure decreased by over 40% from SC23 to SC24.

Magnetic field strength reduced by over 25%, with turbulence also declining.

Non-radial flow components shifted from tangential to normal dominance in SC25.

Abstract

We investigate the evolution of interplanetary coronal mass ejection (ICME) sheath regions at 1 AU across solar cycles 23, 24, and the rising phase of 25, focusing on their variability and turbulence in relation to upstream solar wind conditions and the global heliospheric state. Using a dataset of over 900 ICME sheath events, we apply statistical metrics such as the interquartile range (IQR) and the Turbulence Index (TI) to quantify variability and turbulence. The analysis compares full and rising phases of solar cycles and examines both local ICME parameters (e.g., sheath total pressure, non-radial flows) and global interplanetary indicators such as open solar flux (OSF). From SC23 to SC24, sheath total pressure and magnetic field strength decreased by over 40% and 25%, respectively, accompanied by reduced turbulence and variability. In contrast, the rising phase of SC25 shows increased magnetic complexity, particularly in non-radial field components, despite stable bulk parameters. Non-radial flow patterns also shift from tangentially dominated in SC23-SC24 to normal-dominated in SC25, suggesting changes in ICME orientation and sheath formation mechanisms. No significant correlation is found between OSF and sheath properties, indicating that local solar wind and ICME specific factors are the primary drivers of sheath evolution. The study reinforces the importance of upstream solar wind dynamics in relation to variations in plasma and magnetic field measured components of ICME sheaths. The derived trends in turbulence, magnetic orientation, and flow geometry suggest that sheath regions are sensitive indicators of solar cycle phase and should be considered as distinct, structured components in ICME modeling.