On 28th October 2021 the Sun released a large coronal mass ejection (CME) in Earth's direction. An X1.0 class solar flare and a rare ground level enhancement (GLE) were observed, along with bright solar radio bursts. We explore the inner terrestrial response to this solar event using multi-point measurements from the near-Earth space environment. These measurements include historical solar wind monitors and geomagnetic indices, UV auroral observations from the spectrograph imager SSUSI onboard the DMSP spacecraft, field-aligned current (FAC) measurements from the AMPERE project via the IRIDIUM constellation, and newly accessible auroral kilometric radiation (AKR) observations from Wind (Waters et al. 2021).
The CME and its arrival is tracked at ∼1 AU using remote radio observations from Wind, along with in-situ interplanetary magnetic field (IMF) and solar wind measurements from OMNI. Geomagnetic activity is studied with SYM-H, SuperMAG and PC indices, showing the expected presence of multiple substorm onsets. The dayside auroral response is monitored for the first time with Wind AKR observations from L1, where the highly-directed beaming of AKR from typical nightside sources is not easily observed; the radiated power exceeds the 10 year average from the same local time by 1-2 orders of magnitude and originates from discrete, substorm-associated UV aurora in the afternoon local time sector. This is supported by novel multi-point observations between Wind AKR measurements and FACs from AMPERE, which also allows the dominant acceleration mechanism to be inferred for upward currents between 1400-1800 hours magnetic local time (MLT). During a particular 12 hour period where Wind is least affected by viewing constraints, the Southern hemisphere presents enhanced upward current during multiple, repeat substorm onsets and AKR bursts, suggesting parallel electric field acceleration and Alfvénic acceleration processes are both occurring in this MLT sector. Upward current is then enhanced in both hemispheres during a single substorm onset and is well correlated with the largest observed AKR burst, suggesting dominance of double-layer potential acceleration.
Such exploration of AKR with Wind and assimilation of multiple observed phenomena provides insight into the dynamics of the magnetosphere-ionosphere coupling region via the structure and activation of auroral current systems. This precedes statistical, parametric modelling of the visibility of substorm and similar dynamics for dayside observations from Wind, allowing the spatial distribution of active AKR sources and acceleration processes to be constrained more quantitatively for future use.