Advance warning of high‐speed ejecta based on real‐time shock analyses: When fast‐moving ejecta appear to be overtaking slow‐moving shocks

Abstract

1] Interplanetary shocks propagating into the magnetosphere can have significant space weather consequences. However, for many purposes it is the ejecta behind the shock that is the greater threat. The ejecta can be fast moving, impart significant momentum upon the magnetopause, and may contain a flux rope with strong southward magnetic fields. When transient solar wind activity strikes the magnetosphere, it can lead to enhanced magnetospheric currents and elevated radiation levels in the near-Earth environment. It is therefore desirable to use the observed shocks ahead of ejecta to predict any aspects of the approaching ejecta that can be predicted. We have examined 39 shocks observed by the Advanced Composition Explorer spacecraft in the years 1998 to 2003. Within the selection are shocks that were chosen because they appear to propagate significantly more slowly than the speed of the ejecta behind it. While appearing at first to be a contradiction, we show that the shocks are propagating across the radial direction and at significant angles to the velocity of the ejecta. These slow-moving shocks are actually precursors of fast-moving and potentially significant ejecta. Reversing the analysis, we are able to predict the peak speed of the ejecta well in advance of their observation, up to or in excess of 10 h following the shock crossing, when slow-moving shocks are seen, and we have incorporated this feature into our real-time shock analysis. (2012), Advance warning of highspeed ejecta based on real-time shock analyses: When fast-moving ejecta appear to be overtaking slow-moving shocks, Space Weather, 10, S12002,

Impact Angle Control of Local Intense dB/dt Variations During Shock‐Induced Substorms

“…Global dB/dt maps in North America show that the overall geographic areas with dB/ dt surpassing the thresholds 1.5 and 5 nT/s were generally higher in the 5 April 2010 event, with intense ULF/ Pc5 wave activity occurring at times of maximum areas in both events, but with wave activity being higher in the NFS case compared to the HIS case. Considering that these dB/dt thresholds can cause damage to power grid equipment operating in different timescales (Molinski et al, 2000;Pulkkinen et al, 2013), power plant operators can take advantage of these results to plan ahead and avoid long-term damage associated with space weather effects particularly caused by IP shocks that are observed at L1 and bound to impact Earth nearly head-on (Kruparova et al, 2013;Paulson et al, 2012;Vorotnikov et al, 2011). Tsurutani and Hajra (2021) used over 2 years of GIC data collected in southern Finland to show that 76% of the events with GIC 𝐴𝐴 𝐴 30 A were caused by supersubstorms, whereas all events with GIC 𝐴𝐴 𝐴 10 A were caused by intense substorms.…”

Geomagnetically Induced Currents Caused by Interplanetary Shocks With Different Impact Angles and Speeds

“…Furthermore, the findings of this work may provide insights for direct applications to space weather forecasting. Solar wind monitors at the L1 point such as Wind and ACE offer real‐time solar wind and IMF conditions that are used for automated computations of shock impact angles and speeds (Kruparova et al, ; Paulson et al, ; Vorotnikov et al, , ). Therefore, a 30–60 min window time may provide the opportunity to power plant operators to take actions to prevent GICs that may be triggered by high‐speed and head‐on shocks that will impact the magnetosphere when the station is located around noon LT.…”

A Coronal Mass Ejection and Magnetic Ejecta Observed In Situ by STEREO-A and Wind at 55° Angular Separation

“…The shock normal angle (angle between the shock normal direction and the upstream magnetic field) is found to be ∼62°, corresponding to a quasi-perpendicular shock at STEREO-A. The angle between the shock normal and radial direction, which can be used as an approximation of a spacecraft crossing distance from the CME nose (e.g., Paulson et al 2012;Janvier et al 2015) is ∼34 ±1°. This can be used as an argument that the spacecraft crossing for STEREO-A occurs away from the nose of the shock.…”