Revisiting the Ionospheric Disturbances Over Low Latitude Region of China During Super Typhoon Hato

The ionosphere exhibits complex variations due to the influences from above and below. To distinguish the source of ionospheric disturbances is important for understanding the variation process and the coupling mechanism among different regions. Using the ionospheric total electron content (TEC) derived from Global Navigation Satellite System observations, the ionospheric disturbances during the super typhoon Hato in 2017 that was accompanied by a weak geomagnetic storm are revisited, including the ionospheric deviation and traveling ionospheric disturbances (TIDs). It is found that the ionospheric TEC in the low-latitude region of China experienced a significant enhancement (200% compared to the quiet geomagnetic day) on Hato landing day. This enhancement covers the northern and southern equatorial ionization anomaly (EIA) region from 80 degrees E to 180 degrees E. Considering the geomagnetic condition, the hmF2 and the O/N2 ratio in thermosphere, it is concluded that this enhancement is not related to the typhoon, but to the coinciding weak geomagnetic storm. Additionally, several medium-scale TIDs are verified from differential TEC data in China low latitude region during Hato period. Most of them occur after sunset and their propagating direction is southwest that often occur in East-Asian sector in summer months, which are not related to the typhoon. While a few TIDs with concentric wavefront (Concentric TIDs) are also observed on the day before Hato landfall that should be excited in the deep convective region of the typhoon. Because the ionosphere is affected by disturbances both from above and below, it should be careful to determine the source of the ionospheric disturbances. The ionospheric conditions can be influenced by factors from both above (such as solar flares and geomagnetic storms) and below (including volcanoes, earthquakes, and severe weather disturbances). To distinguish these sources from ionospheric observations is important for understanding the ionospheric variability and is practically necessary for the ionospheric forecast. On the day of Typhoon Hato landfall (23 August 2017), the Total Electron Content (TEC) in the low-latitude region of China experienced a great increase. It is noted that a weak geomagnetic storm also occurred on the landfall day. So, to determine the reasons of this enhancement becomes very interesting. In this study, we revisit ionospheric disturbances using dense Global Navigation Satellite System stations, ionosondes, space environment and meteorological data. Our results demonstrate that the primary source of this TEC enhancement is the weak geomagnetic storm rather than typhoon Hato. Additionally, we analyze several Traveling Ionospheric Disturbances that have different sources during the typhoon period, furtherly clarifying the impact of Hato on the ionosphere. Through this study, we emphasize the importance of the depth and comprehensiveness of relevant research in determining the sources of ionospheric disturbances. Significant ionospheric total electron content increase over low latitude region of China on the day of Hato landfall is not related to typhoon but to the coinciding weak geomagnetic storm Several traveling ionospheric disturbances (TIDs) events are observed in the low latitude region of China during Hato period, but only the concentric TIDs occurred on 22 August 2017 is related to Hato Because the ionosphere is affected by disturbances from above and below, it should be careful to determine the source of disturbances, especially those originating from below