Energetic Electron Precipitation Occurrence Rates Determined Using the Syowa East SuperDARN Radar

Abstract

We demonstrate that the Super Dual Auroral Radar Network (SuperDARN) radar at Syowa station, Antarctica, can be used to detect high frequency radio wave attenuation in the D region ionosphere during energetic electron precipitation (EEP) events. EEP‐related attenuation is identified in the radar data as a sudden reduction in the backscatter power and background noise parameters. We focus initially on EEP associated with pulsating aurora and use images from a colocated all‐sky camera as a validation data set for the radar‐based EEP event detection method. Our results show that high‐frequency attenuation that commences during periods of optical pulsating aurora typically continues for 2–4 hr after the camera stops imaging at dawn. We then use the radar data to determine EEP occurrence rates as a function of magnetic local time (MLT) using a database of 555 events detected in 2011. EEP occurrence rates are highest in the early morning sector and lowest at around 15:00–18:00 MLT. The postmidnight and morning sector occurrence rates exhibit significant seasonal variations, reaching approximately 50% in the winter and 15% in the summer, whereas no seasonal variations were observed in other MLT sectors. The mean event lifetime determined from the radar data was 2.25 hr, and 10% of events had lifetimes exceeding 5 hr.

D-region impact area of energetic particle precipitation during pulsating aurora

“…To perform this estimate, we use the fact that this higher energy precipitation causes enhanced ionisation in the D-region ionosphere, which in turn attenuates high frequency (HF) radiowaves. This attenuation can be detected using Super-DARN HF radars, as previously shown by Bland et al (2019). In this study we build upon this work by using ten SuperDARN radars in Antarctica to estimate the EEP impact area for different types of PsA.…”

“…SuperDARN is a global network of 36 HF radars designed primarily for studying high-latitude plasma convection (Greenwald et al, 1995;Chisham et al, 2007;Nishitani et al, 2019). Recently, the radars have also been used to detect HF radio attenuation during shortwave fadeout events (Watanabe and Nishitani, 2013;Berngardt et al, 2018;Chakraborty et al, 2018;Fiori et al, 2018), polar cap absorption events (Bland et al, 2018;Chakraborty et al, 2019), and auroral absorption events including PsA (Bland et al, 2019). HF radio attenuation events are identified in the SuperDARN radar data as periods of reduced backscatter power combined with a reduction in the background radio noise.…”

Noise level forecasts at 8–20 MHz and their use for morphological studies of ionospheric absorption variations at EKB ISTP SB RAS radar

“…Subsequent statistical analysis according to the data of world-wide radar network showed usefulness of this method in the lit time: it allows approve the main influence of the ionosphere near the radar to the absorption; it allows demonstrate the contributions of D-and E-layers to the absorption; it allows estimate the frequency dependence of absorption; it allows localize the region in which the absorption measured [4]. Studies of absorption associated with the corpuscular solar radiation allow demonstrate a good agreement between radio noise 8-20MHz absorption and standard observations by riometers [2,3], allowing to prove the correctness of the technique in these cases too.…”

“…Frequency dependence of the detected absorption Traditionally it is believed that the absorption of radio waves vertically propagating in the ionosphere has a power-law frequency dependence [16,17,18,19,2,4,3]:…”

“…The use of 8-20MHz radio noise, measured by short-wave radars for the diagnosis of the lower part of the ionosphere, is an intensively developed method [1,2,3,4,5]. The physical processes that cause this effect [4] are close to the physical processes that cause the absorption of the signals scattered from the earth's surface (ground scatter, GS) [6,7], so GS signals and noise level both can be used to study the absorption of radiwaves [5].…”