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

Abstract

In this paper, a method is described for using 8-20MHz noise absorption effect for realtime detecting radiowave absorption periods. The method is based on two empirical autoregression models of noise dynamics. The first (rough) prediction model is based on radar measurements of daily minimal noise dynamics averaged over 28-days with specially calculated weight coefficients. The second (fine) prediction model uses real-time scaling of rough model. The scaling is based on the comparison of this model with the experimental noise observations during previous 5 days. The models are based on the whole EKB ISTP SB RAS radar dataset (2013)(2014)(2015)(2016)(2017)(2018). The rough model allows one to estimate the boundary beyond which the noise variations can be associated with absorption periods with a high degree of certainty. A joint analysis of simultaneous data on neighboring radar beams and at several frequencies reduces the detection errors, and allows to identify absorption events with a higher degree of confidence. Use of fine model allows to estimate absorption. The technique is validated by frequency dependence of absorption during two-frequency measurements. The found frequency dependence has an average exponent of the order of -1.5, which is in good agreement with the literature data and the data obtained earlier in analysis of solar X-ray flares. The use of the detection technique at EKB radar shows that most probable absorption over absorption events is about -0.65dB. Analysis of absorption of different amplitudes shows that low-intensity absorption events (0..-1.3dB) have slight local time dependence and mostly observed at north directions. For the storng absorption events (stronger than -1.3dB) the local time dynamics correlates well with noise level dynamics, and usually fills the whole radar field-of-view.

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

“…This may be possible in the future with improved baselining of the background noise parameter (e.g. Berngardt, 2020), and a better understanding of the sensitivity of SuperDARN radars to PsA-related EEP. For the purposes of atmospheric modelling, however, statistical EEP energy spectra from satellite observations (e.g.…”

“…At the standard SuperDARN operating frequencies of 8-20 MHz, this background radio noise is produced mainly by lightning activity and propagates around the globe via ionospheric reflections. The noise measurements can be used to estimate the attenuation in decibels relative to a radar-specific quiet day curve using an approach analogous to riometry (Bland et al, 2018;Berngardt, 2020). However, due to the high variability of the noise at the SuperDARN operating frequencies, producing quiet day curves is not straightforward and the methodology is still being developed (Berngardt, 2020).…”

“…The noise measurements can be used to estimate the attenuation in decibels relative to a radar-specific quiet day curve using an approach analogous to riometry (Bland et al, 2018;Berngardt, 2020). However, due to the high variability of the noise at the SuperDARN operating frequencies, producing quiet day curves is not straightforward and the methodology is still being developed (Berngardt, 2020). Therefore, in this work we adopt a more qualitative approach based on visual identification of HF attenuation events in quicklook plots.…”

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

“…SuperDARN is a global network of 36 HF radars primarily designed 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 PsAs (Bland et al, 2019). HF radio attenuation events are identified in the Su-perDARN radar data as periods of reduced backscatter power combined with a reduction in the background radio noise.…”

Seasonal and diurnal dynamics of radio noise for 8-20MHz poleward-oriented mid-latitude radars

“…Noise level studies have recently become an integral part of theoretical and applied research on lower ionosphere dynamics during solar flares and coronal mass ejections through the use of SuperDARN and similar high-frequency (HF) radars (Berngardt et al, 2018;Bland et al, 2018;Berngardt et al, 2019;Bland et al, 2019;Berngardt, 2020). HF noise has traditionally been considered to come from a mixture of several components -anthropogenic, cosmic, and atmospheric.…”