Ionospheric electron enhancement immediately before the 2022 January 15 eruption of the Hunga-Tonga Hunga-Ha’apai submarine volcano: A fake precursor caused by space weather

Near-field ionospheric total electron content records before and after the 2022/1/15 eruption of the Hunga-Tonga Hunga-Ha’apai volcano, are studied using GNSS total electron content data. The data started showing positive departures from the afternoon smooth decreasing trend ~ 1 hour before the eruption. This anomaly is localized around the volcano, i.e., it decays as we go away from the volcano. The signature resembles to the one preceded the 2011 Tohoku-oki earthquake. However, a detailed investigation of ionospheric anomalies from a dense GNSS array in New Zealand showed a large-scale traveling ionospheric disturbance propagating toward Tonga, excited by a moderate geomagnetic storm on the previous day. This suggests that the anomaly around the volcano immediately before the eruption was caused by the arrival of this disturbance at Tonga just at the eruption time.