Dynamics of Large Scale Solar Wind Streams Obtained by the Double Superposed Epoch Analysis: 5. Influence of the Solar Activity Decrease

TL;DR

This study analyzes how large-scale solar wind streams and their associated parameters changed during periods of high and low solar activity, revealing consistent profiles but reduced magnitudes during low activity periods.

Contribution

It provides a comparative analysis of solar wind parameters across different solar activity epochs using double superposed epoch analysis, highlighting the stability of profiles but variations in magnitude and flow angles.

Findings

No significant change in driver durations during low activity.

Parameter profiles retain shape but are lower in magnitude during low activity.

Larger variation in solar wind flow angles during low activity.

Abstract

In solar cycles 23-24, solar activity noticeably decreased, and, as a result, solar wind parameters decreased. Based on the measurements of the OMNI base for the period 1976-2019, the time profiles of the main solar wind parameters and magnetospheric indices for the main interplanetary drivers of magnetospheric disturbances (solar wind types CIR, Sheath, ejecta and MC) are studied using the double superposed epoch method. The main task of the research is to compare time profiles for the epoch of high solar activity at 21-22 solar cycles and the epoch of low activity at 23-24 solar cycles. The following results were obtained. (1) The analysis did not show a statistically significant change in driver durations during the epoch of minimum. (2) The time profiles of all parameters for all types of SW in the epoch of low activity have the same shape as in the epoch of high activity, but locate at lower values of the parameters. (3) In CIR events, the longitude angle of the solar wind flow has a characteristic S-shape, but in the epoch of low activity it varies in a larger range than in the previous epoch.