TY - JOUR

T1 - Solar Cycle-Modulated Deformation of the Earth–Ionosphere Cavity

AU - Bozóki, Tamás

AU - Sátori, Gabriella

AU - Williams, Earle

AU - Mironova, Irina

AU - Steinbach, Péter

AU - Bland, Emma C.

AU - Koloskov, Alexander

AU - Yampolski, Yuri M.

AU - Budanov, Oleg V.

AU - Neska, Mariusz

AU - Sinha, Ashwini K.

AU - Rawat, Rahul

AU - Sato, Mitsuteru

AU - Beggan, Ciaran D.

AU - Toledo-Redondo, Sergio

AU - Liu, Yakun

AU - Boldi, Robert

N1 - Publisher Copyright: © Copyright © 2021 Bozóki, Sátori, Williams, Mironova, Steinbach, Bland, Koloskov, Yampolski, Budanov, Neska, Sinha, Rawat, Sato, Beggan, Toledo-Redondo, Liu and Boldi.

PY - 2021/8/26

Y1 - 2021/8/26

N2 - The Earth–ionosphere cavity resonator is occupied primarily by the electromagnetic radiation of lightning below 100 Hz. The phenomenon is known as Schumann resonances (SR). SR intensity is an excellent indicator of lightning activity and its distribution on global scales. However, long-term measurements from high latitude SR stations revealed a pronounced in-phase solar cycle modulation of SR intensity seemingly contradicting optical observations of lightning from satellite, which do not show any significant solar cycle variation in the intensity and spatial distribution of lightning activity on the global scale. The solar cycle-modulated local deformation of the Earth–ionosphere cavity by the ionization of energetic electron precipitation (EEP) has been suggested as a possible phenomenon that may account for the observed long-term modulation of SR intensity. Precipitating electrons in the energy range of 1–300 keV can affect the Earth–ionosphere cavity resonator in the altitude range of about 70–110 km and modify the SR intensities. However, until now there was no direct evidence documented in the literature supporting this suggestion. In this paper we present long-term SR intensity records from eight stations, each equipped with a pair of induction coil magnetometers: five high latitude (|lat| > 60°), two mid-high latitude (50° < |lat| < 60°) and one low latitude (|lat| < 30°). These long-term, ground-based SR intensity records are compared on the annual and interannual timescales with the fluxes of precipitating 30–300 keV medium energy electrons provided by the POES NOAA-15 satellite and on the daily timescale with electron precipitation events identified using a SuperDARN radar in Antarctica. The long-term variation of the Earth–ionosphere waveguide’s effective height, as inferred from its cutoff frequency, is independently analyzed based on spectra recorded by the DEMETER satellite. It is shown that to account for all our observations one needs to consider both the effect of solar X-rays and EEP which modify the quality factor of the cavity and deform it dominantly over low- and high latitudes, respectively. Our results suggest that SR measurements should be considered as an alternative tool for collecting information about and thus monitoring changes in the ionization state of the lower ionosphere associated with EEP.

AB - The Earth–ionosphere cavity resonator is occupied primarily by the electromagnetic radiation of lightning below 100 Hz. The phenomenon is known as Schumann resonances (SR). SR intensity is an excellent indicator of lightning activity and its distribution on global scales. However, long-term measurements from high latitude SR stations revealed a pronounced in-phase solar cycle modulation of SR intensity seemingly contradicting optical observations of lightning from satellite, which do not show any significant solar cycle variation in the intensity and spatial distribution of lightning activity on the global scale. The solar cycle-modulated local deformation of the Earth–ionosphere cavity by the ionization of energetic electron precipitation (EEP) has been suggested as a possible phenomenon that may account for the observed long-term modulation of SR intensity. Precipitating electrons in the energy range of 1–300 keV can affect the Earth–ionosphere cavity resonator in the altitude range of about 70–110 km and modify the SR intensities. However, until now there was no direct evidence documented in the literature supporting this suggestion. In this paper we present long-term SR intensity records from eight stations, each equipped with a pair of induction coil magnetometers: five high latitude (|lat| > 60°), two mid-high latitude (50° < |lat| < 60°) and one low latitude (|lat| < 30°). These long-term, ground-based SR intensity records are compared on the annual and interannual timescales with the fluxes of precipitating 30–300 keV medium energy electrons provided by the POES NOAA-15 satellite and on the daily timescale with electron precipitation events identified using a SuperDARN radar in Antarctica. The long-term variation of the Earth–ionosphere waveguide’s effective height, as inferred from its cutoff frequency, is independently analyzed based on spectra recorded by the DEMETER satellite. It is shown that to account for all our observations one needs to consider both the effect of solar X-rays and EEP which modify the quality factor of the cavity and deform it dominantly over low- and high latitudes, respectively. Our results suggest that SR measurements should be considered as an alternative tool for collecting information about and thus monitoring changes in the ionization state of the lower ionosphere associated with EEP.

KW - DEMETER

KW - earth-ionosphere cavity

KW - energetic electron precipitation

KW - extremely low frequency

KW - Q-factor

KW - Schumann resonance

KW - solar cycle

KW - solar X-rays

KW - SEASONAL-VARIATIONS

KW - PARAMETERS

KW - MONITORING SCHUMANN RESONANCES

KW - ATMOSPHERE

KW - ENERGETIC ELECTRON-PRECIPITATION

KW - LIGHTNING ACTIVITY

KW - FREQUENCY

KW - SUPERDARN

KW - IONIZATION

KW - PROPAGATION

UR - http://www.scopus.com/inward/record.url?scp=85114638263&partnerID=8YFLogxK

UR - https://www.mendeley.com/catalogue/833ac660-15ed-3b67-ba96-7b8e9793e3a0/

U2 - 10.3389/feart.2021.689127

DO - 10.3389/feart.2021.689127

M3 - Article

AN - SCOPUS:85114638263

VL - 9

JO - Frontiers of Earth Science

JF - Frontiers of Earth Science

SN - 1673-7385

M1 - 689127

ER -