Ionospheric plasma structuring in relation to auroral particle precipitation

Abstract

Auroral particle precipitation potentially plays a main role in ionospheric plasma structuring. The impact of auroral particle precipitation on plasma structuring is investigated using multi-point measurements from scintillation receivers and all sky cameras from Longyearbyen, Ny-Ålesund and Hornsund on Svalbard. This provides us with the unique possibility of studying the spatial and temporal dynamics of the aurora. Here we consider three case studies to investigate how plasma structuring is related to different auroral forms. We demonstrate that plasma structuring impacting the GNSS signals is largest at the edges of auroral forms. Here we studied two stable arcs, two dynamic auroral bands and a spiral. Specifically for arcs we find elevated phase scintillation indices at the pole-ward edge of the aurora. This is observed for auroral oxygen emissions (557.7 nm) at 150~km in the ionospheric E-region. This altitude is also used as the ionospheric piercing point for the GNSS signals as the observations remain the same regardless of different satellite elevations and azimuths. Further, there may be a time delay between the temporal evolution of aurora (f.e. commencement and fading of auroral activity) and observations of elevated phase scintillation indices. The time delay could be explained by the intense influx of particles, which increases the plasma density and causes recombination to carry on longer, which may lead to a persistence of structures - a 'memory effect'. High values of phase scintillation indices can be observed even shortly after strong visible aurora and can then remain significant at low intensities of the aurora.

Investigation of Ionospheric Small‐Scale Plasma Structures Associated With Particle Precipitation

“…The E‐region ionospheric plasma is subject to energetic particle beams from the particle precipitation and to collisions with available neutrals. Particle precipitation into the ionospheric E‐region leads to a widespread irregularities and energy dissipation, and it plays a main role in E‐region large‐scale ionospheric plasma structuring (Enengl et al., 2023; Makarevich et al., 2021).…”

“…When the precipitation declines or moves, it will still take some time for the plasma structures to diffuse. During this “memory effect,” instabilities will further structure plasma and dissipate energy (Enengl et al., 2023). On 6th November 2019 (#4), multiple peaks in the auroral intensity (19:00 UT, 19:18 UT, 19:22 UT, 19:26 UT, 19:44 UT, 19:50 UT) are correlated with the peaks in the S4 index, see again Figures 1f and 1h.…”

“…In this work, the auroral emissions were captured by an all‐sky imager (ASI): Keo Sentry 4ix Monochromatic Imager from KEO Scientific, operated by the University of Oslo (Norway) situated in Longyearbyen Svalbard (geographic coordinates: 78.15°N, 16.04°E). The imager is equipped with narrow band‐pass filters to monitor 557.7 nm (green) and 630.0 nm (red) auroral emissions, recording images every 15–30 s. The green auroral emissions are projected to an altitude of 150 km (Enengl et al., 2023; Partamies et al., 2022). The red auroral images were projected to an altitude of 250 km.…”

“…Irregularities on the pole‐ward side of the aurora are predominantly smaller than the Fresnel scale (observed as amplitude scintillation) (Conroy et al., 2022). Plasma structuring as driven by particle precipitation is proposed to be driven at the boundaries of the auroral precipitation (by such instabilities as Kelvin‐Helmholtz and/or Farley‐Buneman) down to E‐region altitudes and to play a main role in plasma structuring on various scales (Enengl et al., 2023). Pole‐ward moving auroral forms can cause stronger ionospheric irregularities, capable of causing more severe disturbances in the cusp ionosphere for navigation signals than polar cap patches (Oksavik et al., 2015).…”

Automated Nighttime Cloud Detection Using Keograms When Aurora Is Present

“…Because of their relationship to interactions with the magnetosphere, researchers have been interested in classifying types of aurorae and correlating them with other events, particularly those having space weather impact. For example, researchers have noted that the passage of aurorae are associated with radio frequency scintillations at high latitudes (Enengl et al., 2023; Hampton et al., 2013; Loucks et al., 2017; Mrak et al., 2018; Semeter et al., 2017) which can adversely affect radio‐based communication and navigation systems such as the Global Positioning System (GPS). The quality of ground‐based auroral images is limited by the presence of clouds in the sky.…”