Global diagnostics of ionospheric absorption during X-ray solar flares based on 8-20MHz noise measured by over-the-horizon radars

Abstract

An analysis of noise attenuation during eighty solar flares between 2013 and 2017 was carried out at frequencies 8-20 MHz using thirty-four SuperDARN radars and the EKB ISTP SB RAS radar. The attenuation was determined on the basis of noise measurements performed by the radars during the intervals between transmitting periods. The location of the primary contributing ground sources of noise was found by consideration of the propagation paths of radar backscatter from the ground. The elevation angle for the ground echoes was determined through a new empirical model. It was used to determine the paths of the noise and the location of its source. The method was particularly well suited for daytime situations which had to be limited for the most part to only two crossings through the D region. Knowing the radio path was used to determine an equivalent vertical propagation attenuation factor. The change in the noise during solar flares was correlated with solar radiation lines measured by GOES/XRS, GOES/EUVS, SDO/AIA, SDO/EVE, SOHO/SEM and PROBA2/LYRA instruments. Radiation in the 1 to 8$\mathring{A}$ and and near 100$\mathring{A}$ are shown to be primarily responsible for the increase in the radionoise absorption, and by inference, for an increase in the D and E region density. The data are also shown to be consistent with a radar frequency dependence having a power law with an exponent of -1.6. This study shows that a new dataset can be made available to study D and E region.

arXiv comment30 pages, 5 figures, 2 tables. Submitted to Space Weather

References in corpus (4)

• The LYRA Instrument Onboard PROBA2: Description and In-Flight Performance
• EUV SpectroPhotometer (ESP) in Extreme Ultraviolet Variability Experiment (EVE): Algorithms and Calibrations
• Attenuation of decameter sky noise during x-ray solar flares in 2013-2017 based on the observations at midlatitude radars
• Correction of SOHO CELIAS/SEM EUV Measurements saturated by extreme solar flare events

Cited by in corpus (2)

• Noise level forecasts at 8-20MHz and their use for morphological studies of ionospheric absorption variations at EKB ISTP SB RAS radar
• Seasonal and diurnal dynamics of radio noise for 8-20MHz poleward-oriented mid-latitude radars