Factors Affecting the Geo-effectiveness of Shocks and Sheaths at 1 AU

Abstract

We identify all fast-mode forward shocks, whose sheath regions resulted in a moderate (56 cases) or intense (38 cases) geomagnetic storm during 18.5 years from January 1997 to June 2015. We study their main properties, interplanetary causes and geo-effects. We find that half (49/94) such shocks are associated with interacting coronal mass ejections (CMEs), as they are either shocks propagating into a preceding CME (35 cases) or a shock propagating into the sheath region of a preceding shock (14 cases). About half (22/45) of the shocks driven by isolated transients and which have geo-effective sheaths compress pre-existing southward Bz. Most of the remaining sheaths appear to have planar structures with southward magnetic fields, including some with planar structures consistent with field line draping ahead of the magnetic ejecta. A typical (median) geo-effective shock-sheath structure drives a geomagnetic storm with peak Dst of -88 nT, pushes the subsolar magnetopause location to 6.3 Re, i.e. below geosynchronous orbit and is associated with substorms with a peak AL-index of -1350 nT. There are some important differences between sheaths associated with CME-CME interaction (stronger storms) and those associated with isolated CMEs (stronger compression of the magnetosphere). We detail six case studies of different types of geo-effective shock-sheaths, as well as two events for which there was no geomagnetic storm but other magnetospheric effects. Finally, we discuss our results in terms of space weather forecasting, and potential effects on Earth's radiation belts.

15 pages, 8 Figures, accepted by JGR

References in corpus (4)

• Shocks inside CMEs: A Survey of Properties from 1997 to 2006
• Impact Angle Control of Interplanetary Shock Geoeffectiveness: A Statistical Study
• Planar magnetic structures in coronal mass ejection-driven sheath regions
• Magnetohydrodynamic Simulation of the Interaction between Interplanetary Strong Shock and Magnetic Cloud and its Consequent Geoeffectiveness

Cited by in corpus (12)

• Satellite orbital drag during magnetic storms
• Turbulent cascade and energy transfer rate in a solar coronal mass ejection
• Importance of CME Radial Expansion on the Ability of Slow CMEs to Drive Shocks
• The effect of stream interaction regions on ICME structures observed in longitudinal conjunction
• Multipoint study of successive coronal mass ejections driving moderate disturbances at 1 AU
• Properties of the Sheath Regions of Coronal Mass Ejections with or without Shocks from STEREO in situ Observations near 1 AU
• Cross helicity of interplanetary coronal mass ejections at 1 au
• Effect of the solar wind density on the evolution of normal and inverse coronal mass ejections
• Forecasting Periods of Strong Southward Magnetic Field Following Interplanetary Shocks
• The Extreme Space Weather Event in February/March 1941
• First direct observations of interplanetary shock impact angle effects on actual geomagnetically induced currents: The case of the Finnish natural gas pipeline system
• Which Upstream Solar Wind Conditions Matter Most in Predicting Bz within Coronal Mass Ejections