Immediate effects of the Hunga Tonga - Hunga Ha’apai volcanic eruption on the AC and DC Global Electric Circuits

Abstract

Observed responses of the AC and DC parts of the Global Electric Circuit (GEC) to the large eruption of the Hunga Tonga - Hunga Ha’apai (HT-HH) volcano on 15 January, 2022 are presented. The AC-related investigation is based on Schumann resonance (SR) measurements from the Nagycenk Geophysical Observatory (NCK), Hungary as well as from distant stations on the globe belonging to the HeartMath Institute (https://www.heartmath.org/gci/). The DC-related investigation is based on atmospheric electric potential gradient measurements (PG) from six recording stations in Europe and in the USA. The GLD360 and the WWLLN lightning detection networks were used to characterize lightning activity in the vicinity of the HT-HH island on the investigated day. The peak lightning stroke rate reached 80/s (5000/minute), whereas the average global rate is ~44/s. Lightning discharges occurred in rings around the vent of the volcano. Peak currents and the diameter of the ring of positive and negative polarity lightning strokes varied differently in the main phase of the eruption. At its peak, negative lightning dominated the electric activity in the volcanic cloud.A global intensification of SR is apparent in connection with the enhanced lightning activity caused by the eruption. The SR data together with the global network observations indicate that the lightning activity in the eruption dominates the naturally occurring global activity for a period of at least one hour. The highly localized increase in lightning activity over HT-HH provides a unique point source of excitation for the SR.In contrast with the dramatic response of the AC global circuit, the response of the DC GEC to this exceptional eruption is not readily unambiguous in the PG measurements. The observations suggest that impulse-like charging of the GEC by ~15% via -CG lightning strokes took place two times during the eruption. A time constant of 7 or 8 minutes has been inferred for near-surface electric field changes from these enhancements. This could be the first direct measurement of the time constant of the GEC near the Earth’s surface, as well as the first observation of the direct charging of the DC GEC by a single atmospheric electrified source.