Dynamics of large-scale solar-wind streams obtained by the double superposed epoch analysis

TL;DR

This study analyzes the temporal behavior of plasma and magnetic field parameters in various large-scale solar wind types using double superposed epoch analysis, revealing similarities between Sheath and CIR regions and their impact on magnetospheric activity.

Contribution

It introduces a novel application of double superposed epoch analysis to compare different solar wind types and their interactions over a multi-decade period.

Findings

Sheath and CIR regions show similar parameter behaviors.

High-speed streams and ICMEs act as pistons compressing plasma.

Compression regions and interplanetary shocks increase magnetospheric activity.

Abstract

Using the OMNI data for period 1976-2000 we investigate the temporal profiles of 20 plasma and field parameters in the disturbed large-scale types of solar wind (SW): CIR, ICME (both MC and Ejecta) and Sheath as well as the interplanetary shock (IS). To take into account the different durations of SW types, we use the double superposed epoch analysis (DSEA) method: re-scaling the duration of the interval for all types in such a manner that, respectively, beginning and end for all intervals of selected type coincide. As the analyzed SW types can interact with each other and change parameters as a result of such interaction, we investigate separately 8 sequences of SW types: (1) CIR, (2) IS/CIR, (3) Ejecta, (4) Sheath/Ejecta, (5) IS/Sheath/Ejecta, (6) MC, (7) Sheath/MC, and (8) IS/Sheath/MC. The main conclusion is that the behavior of parameters in Sheath and in CIR are very similar both qualitatively and quantitatively. Both the high-speed stream (HSS) and the fast ICME play a role of pistons which push the plasma located ahead them. The increase of speed in HSS and ICME leads at first to formation of compression regions (CIR and Sheath, respectively), and then to IS. The occurrence of compression regions and IS increases the probability of growth of magnetospheric activity.