Observation of ionospheric Alfven resonator with double spectral resonance structures at low latitude station, Shillong ($$dipole L=1.08$$)

Abstract

Spectral Resonance Structures (SRS) of Ionospheric Alfven Resonator (IAR) are investigated by analysing the magnetic field data of a high sampling frequency induction coil magnetometer, installed at a low latitude Indian station, Shillong$$(25.56^\circ N, 91.86^\circ E, dipole L=1.08 )$$ ( 25 . 56 ∘ N , 91 . 86 ∘ E , d i p o l e L = 1.08 ) . One of the distinguishing features of IAR resonance structure observed at this latitude is the excitation of two spectral resonance structures simultaneously, one with a small frequency separation and the other with a large frequency separation of subsequent harmonics. The seasonal variation shows that the occurrence of double SRS is more favoured during winter, where, out of the total IAR events observed during winter, about $$47\%$$ 47 % show clear signatures of double SRS and no double SRS are observed during summer. We have examined the altitudinal variation of refractive index using IRI 2016 model to understand the role of local ionospheric conditions in the formation of double spectral resonance structures. Our study reveals that the excitation of double SRS is related to the E-region to F-region variability of refractive index of the ionosphere. We also report that the double spectral resonance structures at Shillong are always observed only in the $${B}_{x}$$ B x component of the magnetic field variation. Graphical Abstract

Day‐To‐Day Quantification of Changes in Global Lightning Activity Based on Schumann Resonances

“…The Bharati (BRT) and Shillong (SHI) stations are operated by the Indian Institute of Geomagnetism. The low resolution (64 Hz) data from the low latitude SHI station in India have been used to study ionospheric Alfven resonances (IAR) (e.g., Adhitya et al., 2022) while high resolution (256 Hz) data from the Antarctic BRT station have been used to examine finer structures of electromagnetic ion cyclotron (EMIC) waves (e.g., Kakad et al., 2018; Upadhyay et al., 2022). The Eskdalemuir (ESK) station is operated by the British Geological Survey and is dedicated to study SRs and ionospheric Alfven resonances (see e.g., Beggan & Musur, 2018; Musur & Beggan, 2019).…”

“…The Bharati (BRT) and Shillong (SHI) stations are operated by the Indian Institute of Geomagnetism. The low resolution (64 Hz) data from the low latitude SHI station in India have been used to study ionospheric Alfven resonances (IAR) (e.g., Adhitya et al, 2022) while high resolution (256 Hz) 1.…”

Anticorrelation Between Sunspot Number and Spectral Resonance Structures of ELF Magnetic Variations Detected at Kawatabi, Miyagi, Japan

“…This is called a spectral resonance structure (SRS) and was found by Belyaev et al [1,2] for the first time at a midlatitude station with an L value of 2.65. The SRSs were detected at high (L ¼ 5.2) [3], mid (L ¼ 2.1) [4], and low latitudes (L ¼ 1.3, 1.2, 1.08) [5][6][7]. All the SRSs were observed during the night [3][4][5][6][7], and the occurrence rate was high during the September to January periods [3,4].…”

“…The SRSs were detected at high (L ¼ 5.2) [3], mid (L ¼ 2.1) [4], and low latitudes (L ¼ 1.3, 1.2, 1.08) [5][6][7]. All the SRSs were observed during the night [3][4][5][6][7], and the occurrence rate was high during the September to January periods [3,4]. The frequency difference between adjacent maxima increased in winter [4,5].…”

A Schumann Resonance-based Quantity for Characterizing Day-to-day Changes in Global Lightning Activity

“…The BRT and SHI stations are operated by the Indian Institute of Geomagnetism. The low resolution (64 Hz) data from the low latitude SHI station in India have been used to study ionospheric Alfven resonances (IAR) (e.g., Adhitya et al, 2022) while high resolution ( 256Hz) data from the Antarctic BRT station have been used to examine finer structures of electromagnetic ion cyclotron (EMIC) waves (e.g., .…”