Investigating energetic electron precipitation through combining ground‐based and balloon observations

Abstract

A detailed comparison is undertaken of the energetic electron spectra and fluxes of two precipitation events that were observed in 18/19 January 2013. A novel but powerful technique of combining simultaneous ground‐based subionospheric radio wave data and riometer absorption measurements with X‐ray fluxes from a Balloon Array for Relativistic Radiation‐belt Electron Losses (BARREL) balloon is used for the first time as an example of the analysis procedure. The two precipitation events are observed by all three instruments, and the relative timing is used to provide information/insight into the spatial extent and evolution of the precipitation regions. The two regions were found to be moving westward with drift periods of 5–11 h and with longitudinal dimensions of ~20° and ~70° (1.5–3.5 h of magnetic local time). The electron precipitation spectra during the events can be best represented by a peaked energy spectrum, with the peak in flux occurring at ~1–1.2 MeV. This suggests that the radiation belt loss mechanism occurring is an energy‐selective process, rather than one that precipitates the ambient trapped population. The motion, size, and energy spectra of the patches are consistent with electromagnetic ion cyclotron‐induced electron precipitation driven by injected 10–100 keV protons. Radio wave modeling calculations applying the balloon‐based fluxes were used for the first time and successfully reproduced the ground‐based subionospheric radio wave and riometer observations, thus finding strong agreement between the observations and the BARREL measurements.

On the Effects of Bremsstrahlung Radiation During Energetic Electron Precipitation

“…These more energetic photons can propagate further distances in the atmosphere before being eventually absorbed, corresponding to the production of Compton electrons at lower altitudes (see Figure a). Another consequence of this difference has been extensively observed by BARREL: a significant amount of low‐energy photons would be absorbed by the atmosphere before penetrating into the stratosphere, thereby leading to the reduction of X‐ray flux in the energy range below ∼30 keV (e.g., Clilverd et al, ; Woodger et al, ). Furthermore, as shown in Figure b, large quantities of photoelectrons and Compton electrons also can be produced at the altitude of the BARREL payloads.…”

Ionization of the Polar Atmosphere by Energetic Electron Precipitation Retrieved From Balloon Measurements

“…Precipitating electron fluxes are subject of high variability as observed by many experiments (Clilverd et al, ; Cresswell‐Moorcock et al, ; Mironova et al, ; Nesse Tyssøy et al, ; Woodger et al, ). Here we show the difference between IR from the CMIP6 data set and retrieved from balloon measurements (Makhmutov et al, ).…”

“…Information about EEP is usually obtained by satellite instruments, such as National Oceanic and Atmospheric Administration Polar-orbiting Operational Environmental Satellites (e.g., Nesse Tyssøy et al, 2016) or Van Allen Probes (e.g., Shprits et al, 2016). Some information can also be obtained from observation of radio wave propagation (Clilverd et al, 2017). Precipitating energetic electrons also generate X-ray and gamma-ray bremsstrahlung which can be detected by stratospheric balloon experiments (Makhmutov et al, 2016;Millan et al, 2013;Woodger et al, 2015).…”

“…A variety of these processes leads to strong variability of EEP and their dependence on the interplanetary disturbance type, site of observation, local magnetic time, and energy of precipitating electrons. A high EEP interdaily variability has been observed in many experiments (Clilverd et al, 2017;Cresswell-Moorcock et al, 2013;Mironova et al, 2015;Nesse Tyssøy et al, 2016;Woodger et al, 2015). Moreover, the electron energy spectrum used for the IR calculations in the CMIP6 project (Matthes et al, 2017) was limited (to 30 keV to <1 MeV), and the lack of electrons with higher energies can lead to some underestimation of the IR below 1 hPa (altitude less than ∼50 km).…”

Demonstrating the Use of a Class of Min‐Max Smoothers for D Region Event Detection in Narrow Band VLF Phase

“…Very low frequency (VLF) waves propagating subionospherically in the Earth‐ionosphere waveguide respond to changing ionospheric conditions by changes in phase and amplitude. Therefore, observed perturbations to the otherwise constant carrier‐phase of man‐made VLF transmissions are routinely used as a sounding device of the bottom‐side ionosphere (e.g., Clilverd et al, ). Characteristic changes in the number and energy density of charged electrons in the D region ionosphere (approximately 50–90 km altitude) signify the occurrence of events such as precipitation of electrons from the radiation belts due to wave‐particle interactions (e.g., Rodger et al, ), increased ionization due to high X‐ray flux following solar flares (e.g., Thomson et al, ), and electron precipitation during substorm injection events (Clilverd et al, ).…”