Storm time, short‐lived bursts of relativistic electron precipitation detected by subionospheric radio wave propagation

Abstract

[1] In this study we report on ground-based observations of short bursts of relativistic electron precipitation (REP), detected by a subionospheric propagation sensor in Sodankylä, Finland during 2005. In two $4 hour case study periods from L = 5.2, around local midnight, several hundred short-lived radio wave perturbations were observed, covering a wide range of arrival azimuths. The vast majority ($99%) of these perturbations were not simultaneous with perturbations on other paths, consistent with a precipitation ''rainstorm'' producing ionospheric changes of small spatial sizes around the Sodankylä receiver. The recovery time of these radio wave perturbations are $1.2 s, which is consistent with the modeled effects of a burst of >2 MeV precipitating electrons. This agrees with satellite observations of the microburst energy spectrum. The energetic nature of the precipitation which produces the FAST perturbations suggests that they should be observable in both day and night conditions. While it is widely assumed that satellite-detected REP microbursts are due to wave-particle interactions with very low-frequency chorus waves, the energy spectra predicted by our current models of chorus propagation and wave-particle interaction are not consistent with the experimentally observed radio wave perturbations presented here or previously reported satellite observations of REP microbursts. The results inferred from both the satellite and subionospheric observations, namely the absence of a large, dominant component of <100 keV precipitating electrons, fundamentally disagrees with a mechanism of chorusdriven precipitation. Nonetheless, further work on the modeling of chorus-driven precipitation is required.Citation: Rodger, C. J., M. A. Clilverd, D. Nunn, P. T. Verronen, J. Bortnik, and E. Turunen (2007), Storm time, short-lived bursts of relativistic electron precipitation detected by subionospheric radio wave propagation,

Relativistic microburst storm characteristics: Combined satellite and ground-based observations

“…Rodger et al [2007] showed the latter result is consistent with the modeled ionosphere recovery of ionization increases produced at altitudes as low as 40-60 km due to REP with energies >2 MeV. The shorter 21 January 2005 decay time was explained by the upper parts of the REPproduced ionization changes being "masked" by excess ionization because of proton precipitation during a solar proton event.…”

Impact of different energies of precipitating particles on NOx generation in the middle and upper atmosphere during geomagnetic storms

“…We are then able to compare the increase in NO x and electron number density as a result of the precipitation. The case events studied here are: an example of high levels of proton precipitation flux as seen in the Halloween storm of October 2003; pulsed auroral precipitation from Ulich et al (2000); REP from Gaines et al (1995) lasting several hours such as those observed by balloon experiments (Millan et al, 2002); and relativistic microbursts from Rodger et al (2007a).…”

“…Energetic particles are ultimately lost to the atmosphere through interactions with magnetospheric waves such as chorus, plasmaspheric hiss, electromagnetic ion cyclotron waves (EMIC), and Pc5 micropulsations. The altitudes at which these particles deposit their momentum is dependent on their energy spectrum, with lower energy particles impacting the atmosphere at higher altitudes than their more energetic relatives (Rees, 1989;Rodger et al, 2007a).…”

Study of Antarctic-South America Connectivity From Ionospheric Radio Soundings

“…Fast VLF perturbations were also observed during rainstorm type precipitation of relativistic electrons of energies E > 2MeV (Rodger et al 2007), in close association with increases of the relativistic electrons flux in the radiation belts. This suggests that during geomagnetic storms the electron precipitating events are closely related with mechanisms in the inner magnetosphere, where intense whistler-mode chorus waves can be generated during the impact of high Speed Solar Wind Streams -hSSWSs (Summers et al 2004).…”

“…The most important space weather phenomena impacting the lower ionosphere are the geomagnetic storms, which affect substantially both at mid-and high-latitudes, as well solar proton events (SPEs) (e.g. Lastovicka 2009) and relativistic electron precipitation (REP) events (Rodger et al 2007).…”