Characteristics of Ionospheric Alfvén Resonator (IAR) observed at Shillong (L=1.13)

Abstract

Ionospheric Alfven Resonator (IAR) is the spectral resonance structures (SRS) in the frequency range of 0.1-10 Hz, as observed in the in the background noise of geomagnetic field variations. Data of the search coil magnetometer operated at Shillong (25.56° N, 91.86° E) is analyzed for the year 2018, to study the characteristics of IAR at low latitude (L=1.13). The study of seasonal dependence of IAR shows that the occurrence of IAR is more during winter as compared to summer, with a minimum occurrence near equinox period. The study also shows a weak dependence of IAR on the geomagnetic activity. The analysis also reveals the presence of double spectral resonance structures (SRS), with large spectral resonance structures appearing along with fine spectral resonance structures. The frequency separation ( Δ f) between the harmonics is calculated using the analytical model by Polyakov and Rapoport [1981] and it is compared with the observed Δ f values. The ionospheric cavity in which these resonance structures are being excited are studied by considering the variation of refractive index using the IRI 2016 model.