CME Evolution in the Structured Heliosphere and Effects at Earth and Mars During Solar Minimum

TL;DR

This study analyzes the origin, evolution, and heliospheric impact of two CMEs and a high-speed stream during solar minimum, revealing their interactions, deflections, and effects at Earth and Mars, emphasizing the importance of accurate solar wind modeling.

Contribution

It provides detailed insights into CME-HSS interactions and their effects during solar minimum, highlighting the significance of heliospheric modeling for space weather prediction.

Findings

First CME impacted both Earth and Mars.

Second CME caused a strong magnetic storm at Earth.

CME-HSS interaction led to CME deflection and rotation.

Abstract

The activity of the Sun alternates between a solar minimum and a solar maximum, the former corresponding to a period of "quieter" status of the heliosphere. During solar minimum, it is in principle more straightforward to follow eruptive events and solar wind structures from their birth at the Sun throughout their interplanetary journey. In this paper, we report analysis of the origin, evolution, and heliospheric impact of a series of solar transient events that took place during the second half of August 2018, i.e. in the midst of the late declining phase of Solar Cycle 24. In particular, we focus on two successive coronal mass ejections (CMEs) and a following high-speed stream (HSS) on their way towards Earth and Mars. We find that the first CME impacted both planets, whilst the second caused a strong magnetic storm at Earth and went on to miss Mars, which nevertheless experienced space weather effects from the stream interacting region (SIR) preceding the HSS. Analysis of remote-sensing and in-situ data supported by heliospheric modelling suggests that CME--HSS interaction resulted in the second CME rotating and deflecting in interplanetary space, highlighting that accurately reproducing the ambient solar wind is crucial even during "simpler" solar minimum periods. Lastly, we discuss the upstream solar wind conditions and transient structures responsible for driving space weather effects at Earth and Mars.