Diverse Ionospheric Disturbances by the 2022 Hunga Tonga‐Hunga Ha'apai Eruption Observed by a Dense GNSS Array in New Zealand

Using a network of global navigation satellite systems receivers in New Zealand, located2,000–3,300 km southwest of Hunga Tonga-Hunga Ha'apai volcano, we found at least three different kindsof ionospheric disturbances from changes in total electron contents (TEC). Ionospheric signatures of thenear-field acoustic wave propagating ∼0.8 km/s were not clear in New Zealand due possibly to large geometricdecay. The first disturbance emerged ∼1 hr after the eruption and traveled toward southwest with a speed of∼0.6 km/s. This, together with the subsequent disturbance propagating by ∼0.4 km/s, suggests its link to theahead-of-tsunami ionospheric disturbance, excited by the Lamb wave and subsequent tsunamis traveling in thePacific Ocean. The second disturbance started ∼2 hr after the eruption as tens of waves with periods 10–15 minpropagating by ∼0.3 km/s, possibly internal gravity waves (IGW) excited by the passages of the Lamb wave.Such IGW wave trains continued until ∼10 hr after the eruption. The Lamb wave traveled round the earth, andits second and third passages disturbed the ionosphere in New Zealand on the next day as similar IGW wavetrains following the Lamb wave. The third disturbance occurred as an enhancement of the harmonic oscillationof TEC with frequency of ∼3.7 mHz, ∼14 hr after the eruption. This might be an atmospheric mode excited bythe eruption, but its propagation and sudden activation remain unexplained.