D‐Region Changes and Wave Activity Detected From Unusually Strong VLF Anomalies Associated With the January 2022 Tonga Volcanic Eruption

Kumar, Sushil and Kumar, Sarwan and Ichihara, Mic (2025) D‐Region Changes and Wave Activity Detected From Unusually Strong VLF Anomalies Associated With the January 2022 Tonga Volcanic Eruption. JGR Space Physics, 130 (11). pp. 1-18. ISSN ISSN 2169-9402

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Abstract

We present unusually strong daytime signal amplitude anomalies of 11.1 dB on JJI and 12.6 dB on VTX very low‐frequency (VLF) transmitter signals recorded at Suva, Fiji, due to the powerful Hunga Tonga– Hunga Ha'apai (HTHH) volcanic eruption (VE) on 15 January 2022 around 04:00 UT. Statistical analysis of daytime trends, daytime and nighttime fluctuations, and dispersion of VLF anomalies showed that VLF anomalies were indeed associated with HTHH VE. The combined effect of long‐duration strong ionization produced by exceptionally intense volcanic lightning detected and Atmospheric Gravity Waves (AGWs) and Lamb Waves (LWs) associated with HTHH VE are reported here as causes of unusually strong VLF amplitude anomalies and D‐region electron density changes. The daytime VLF anomalies extended into nighttime with reduced level that can be attributed to AGWs due to sustained HTHH volcanic lightning activity, as reported in
the literature. Using the Long Wave Propagation Capability (code V2.1), we modeled VLF anomalies and found significant changes in the D‐region VLF reference height (H′) and electron density gradient (β). The H′ for JJI path decreased significantly by 3.2 km, and β increased by 0.319 km� 1, giving an electron density increase from 1.83 × 102 cm� 3 to 1.34 × 103 cm� 3 at the normal daytime H′ of 75.1 km. The perturbations in the D‐region ionosphere are attributed to strong AGWs, mostly of frequency 0.10–0.30 mHz and LWs obtained using Morlet wavelet analysis of VLF anomalies, along with tremendously high lightning strokes demonstrating coupling
between the atmosphere and the D‐region.

Item Type:	Journal Article
Uncontrolled Keywords:	transmitter, nighttime fluctuations, Propagation Capability
Subjects:	Q Science > Q Science (General)
Divisions:	School of Information Technology, Engineering, Mathematics and Physics (STEMP)
Depositing User:	Nirma Narayan
Date Deposited:	08 Dec 2025 03:48
Last Modified:	08 Dec 2025 03:48
URI:	https://repository.usp.ac.fj/id/eprint/15198

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