Pre-earthquake Ionospheric Anomalies and Ionospheric Storms Observed by FORMOSAT-5/AIP and GIM TEC

Abstract

The mission of Advanced Ionospheric Probe (AIP) onboard FORMOSAT-5 (F5) satellite is to detect pre-earthquake ionospheric anomalies (PEIAs) and observe ionospheric space weather. F5/AIP plasma quantities in the nighttime of 22:30 LT (local time) and the total electron content (TEC) of the global ionosphere map (GIM) are used to study PEIAs of an M7.3 earthquake in the Iran–Iraq border area on 12 November 2017, as well as signatures of two magnetic storms on 7 and 21–22 November 2017. Statistical analyses of the median base and one sample test are employed to find the characteristics of temporal PEIAs in GIM TEC over the Iran–Iraq area. The anomalous increases of the GIM TEC and F5/AIP ion density over the epicenter area on 3–4 November (day 9–8 before the M7.3 earthquake) agree with the temporal PEIA characteristics that the significant TEC increase frequently appears on day 14–6 before 53 M ≥ 5.5 earthquakes in the area during 1999–2016. The spatial analyses together with odds studies show that the PEIAs frequently appear specifically over the epicenter day 9–8 before the M7.3 earthquake and day 10–9 before a M6.1 earthquake on 1 December, while proponent TEC increases occur at worldwide high latitudes on the two magnetic storm days. The F5/AIP ion velocity uncovers that the PEIAs of the two earthquakes are caused by associated eastward electric fields, and the two positive storm signatures are due to the prompt penetration electric fields.