Solar Wind Properties and Geospace Impact of Coronal Mass Ejection‐Driven Sheath Regions: Variation and Driver Dependence

Abstract

We present a statistical study of interplanetary conditions and geospace response to 89 coronal mass ejection-driven sheaths observed during Solar Cycles 23 and 24. We investigate in particular the dependencies on the driver properties and variations across the sheath. We find that the ejecta speed principally controls the sheath geoeffectiveness and shows the highest correlations with sheath parameters, in particular in the region closest to the shock. Sheaths of fast ejecta have on average high solar wind speeds, magnetic (B) field magnitudes, and fluctuations, and they generate efficiently strong out-of-ecliptic fields. Slow-ejecta sheaths are considerably slower and have weaker fields and field fluctuations, and therefore they cause primarily moderate geospace activity. Sheaths of weak and strong B field ejecta have distinct properties, but differences in their geoeffectiveness are less drastic. Sheaths of fast and strong ejecta push the subsolar magnetopause significantly earthward, often even beyond geostationary orbit. Slow-ejecta sheaths also compress the magnetopause significantly due to their large densities that are likely a result of their relatively long propagation times and source near the streamer belt. We find the regions near the shock and ejecta leading edge to be the most geoeffective parts of the sheath. These regions are also associated with the largest B field magnitudes, out-of-ecliptic fields, and field fluctuations as well as largest speeds and densities. The variations, however, depend on driver properties. Forecasting sheath properties is challenging due to their variable nature, but the dependence on ejecta properties determined in this work could help to estimate sheath geoeffectiveness through remote-sensing coronal mass ejection observations.

Cosmic noise absorption signature of particle precipitation during ICME sheaths and ejecta

“…CNA values tend to be somewhat higher in the middle of the sheath and ejecta than at their boundaries, but no obvious temporal trends can be detected from the superposed plot. This is consistent with the fact that southward fields in sheaths and ejecta (during which the strongest CNA is expected) can occur anywhere in these structures (e.g., Huttunen et al, 2005;Kilpua et al, 2019a). Flux rope-type ejecta show a solar cycle trend in their magnetic polarity (e.g., Bothmer and Schwenn, 1998), but since our data set covers almost two solar cycles no clear effect from this is expected.…”

“…The events in this study are selected from the list of sheath regions published in Kilpua et al (2019a) for the years 1997…”

Effects of Nearly Frontal and Highly Inclined Interplanetary Shocks on High‐Latitude Field‐Aligned Currents (FACs)

“…In addition to the effect of IP shocks, Kilpua et al () report that the sheaths following the IP shocks of fast ejecta have on average high solar wind speeds, magnetic ( B ) field magnitudes, and fluctuations and generate efficiently strong out‐of‐ecliptic fields. Thus, for the top events in our study (75% quantile), a combination of factors including fast ejecta, NFSs association with the shock nose structure, and subsequent sheath features may play a role in post shock geoeffectiveness.…”

Estimating Satellite Orbital Drag During Historical Magnetic Superstorms

“…CMEs usually have a shock at their leading edge that is promptly followed by a sheath and a magnetic cloud (Balan et al, 2014;Gonzalez et al, 1994;Kilpua et al, 2019). Extreme magnetic storms are caused by the impact of extremely fast CMEs on the Earth's magnetosphere (Tsurutani & Lakhina, 2014), usually associated with highly depressed values of the southward component of the interplanetary magnetic field (Balan et al, 2014;Daglis et al, 1999;Gonzalez et al, 1994;Kilpua et al, 2019;Tsurutani & Lakhina, 2014). Extreme space weather events like severe magnetic storms have been recognized by the U.S. Federal Government through the National Space Weather Strategy and Action Plan (National Science and Technology Council, 2015a, 2015b) as a natural hazard, and the need to establish benchmarks for extreme space weather events has also been recognized by the scientific community (e.g., Jonas, Murtagh, & Bonadonna, 2017;Lanzerotti, 2015;Riley et al, 2018).…”