An investigation of PPP degradations over Asia-Pacific region during Tonga volcanic eruption on 15 January 2022

Abstract

On 15 January 2022, a significant volcanic eruption occurred at Hunga Tonga-Hunga Ha’apai (HTHH), causing global ionospheric disturbances. To investigate ionospheric anomalies and the kinematic GNSS PPP responses to this volcanic eruption over the Asia-Pacific region, the rate of the total electron content index (ROTI) map derived from about 1100 GNSS stations data and ionospheric scintillation indices S4 and σφ are used. We first selected data from six stations for kinematic PPP experiments. Multi-constellation and multi-frequency Precision Positioning (GAMP) software and GNSS analysis software are employed in the process. We then found that the positioning errors of three directions (east, north, up) during disturbance time are larger than those on an ionospheric quiet day (3 January 2022). To explore the reasons for PPP degradation, we conduct a quality analysis of GNSS data on these two days, including carrier-to-noise power-density ratio (C/N0) and the number of cycle slips. The number of satellites affected by cycle slips increased obviously in the disturbance time. The statistics of cycle slip occurrence rate at low latitudes is 12.35 % while that on ionospheric quiet day is only 6.05 %. The strategy of expanding the cycle slip detection thresholds from 0.15 m to 1.5 m for phase geometry free (PGF) combination and 5 cycles to 12 cycles for Hatch–Melbourne-Wübbena (HMW) combination failed to significantly improve the PPP solutions based on data from 357 stations. It was found that only increasing the detection thresholds could not mitigate the PPP degradations. Our investigations contribute to the study of space weather and kinematic GNSS PPP responses to volcanic eruptions.