Electron precipitation characteristics during isolated, compound and multi-night substorm events

Abstract

Abstract. A set of 24 isolated, 46 compound and 36 multi-night substorm events from the years 2008–2013 have been analysed in this study. Isolated substorm events are defined as single expansion-recovery phase pairs, compound substorms consist of multiple phase pairs, and multi-night substorm events refer to recurring substorm activity on consecutive nights. Approximately 200 nights of substorm activity observed over the Fennoscandian Lapland have been analysed for their magnetic disturbance magnitude and the level of cosmic radio noise absorption. Substorm events were automatically detected from the local electrojet index data and visually categorised. We show that isolated substorms have limited lifetimes and spatial extents, as compared to the other substorm types. The average intensity (both in absorption and ground-magnetic deflection) of compound and multi-night substorm events is similar. For multi-night substorm events, the first night is rarely associated with the strongest absorption. Instead, the high-energy electron population needed to cause the strongest absorption builds up over 1–2 additional nights of substorm activity. The non-linear relationship between the absorption and the magnetic deflection at high and low activity conditions is also discussed. We further collect in-situ particle spectra for expansion and recovery phases to construct median precipitation fluxes at energies from 30 eV up to about 800 keV. In the expansion phases the bulk of the spectra shows a local maximum flux in the range of a few keV to 10 keV, while in the recovery phases higher fluxes are seen in the range of tens of keV to hundreds of keV. These findings are discussed in the light of earlier observations of substorm precipitation and their atmospheric effects.

Ionospheric Electron Density and Conductance Changes in the Auroral Zone During Substorms

“…According to them, although the diffuse electron precipitation at keV-10 keV energies provides a major contribution to the precipitated energy flux during substorms, observationally, it is limited within the 22-09 MLT sector, and its intense part does not propagate past the 06 h MLT meridian. Partamies et al, 2021 have shown that high energy electron tens-hundreds keV tends to be observed during the recovery phase of substorm, while during expansion phase electron energy is between few -10 keV. The depletion of keV-tens keV particle flux could most probably be explained by their precipitation losses.…”

A New MEPED‐Based Precipitating Electron Data Set

“…The advantage of using Delaunay triangulation to map the data is that it can capture small‐scale features such as substorm activity that would be averaged out in other data sets. There is a disadvantage in that substorm activity will effectively persist for a day at a time since the maps have 1‐day resolution; in reality, these storms most likely have durations of minutes to hours (Beharrell et al., 2015; Cresswell‐Moorcock et al., 2013; Partamies et al., 2021). On the other hand, it is likely that not all substorms are observed, particularly in a year like 2003 when only three POES satellites were operational.…”

Examination of Radiation Belt Dynamics During Substorm Clusters: Magnetic Local Time Variation and Intensity of Precipitating Fluxes

“…Thus there is increasing evidence that magnetospheric substorms, which are known to enhance chorus activity, lead to significant EEP into the atmosphere (Beharrell et al., 2015; Partamies et al., 2021). There is also evidence that multiple substorms should lead significant decreases in magnetospheric ozone (Seppälä et al., 2015), caused by substorm‐triggered EEP spanning a wide range of magnetic latitudes (Cresswell‐Moorcock et al., 2013).…”