Total electron content anomalies associated with global VEI4+ volcanic eruptions during 2002–2015 Wang Li a,b , Jinyun Guo b, ⁎, Jianping Yue a , Yi Shen b , Yang Yang c a College of Earth Science and Engineering, Hohai University, Nanjing 211100, China b College of Geodesy and Geomatics, Shandong University of Science and Technology, Qingdao 266590, China c SPACE Research Centre, RMIT University, Melbourne, Victoria, Australia abstract article info Article history: Received 12 October 2015 Received in revised form 21 June 2016 Accepted 22 June 2016 Available online 23 June 2016 In previous studies, little attention has been paid to the total electron content (TEC) anomalies preceding the vol- canic eruption. We analyze the coupling relationship between volcanic eruption and TEC anomalies, and discuss the spatial distribution of TEC anomalies associated with volcanic geographical location. We utilize the global ion- osphere map (GIM) data from the Center for Orbit Determination in Europe (CODE) to analyze TEC variations be- fore the global volcanic eruptions indicated by VEI (Volcanic Explosivity Index) 4+ from 2002 to 2015 with the sliding interquartile range method. The results indicate the occurrence rate of TEC anomalies before great volca- nic eruptions is related with the volcanic type and geographical position. The occurrence rate of TEC anomalies before stratovolcano and caldera eruptions is higher than that before shield and pyroclastic shield eruptions, and the occurrence rate of TEC anomalies has a descending trend from low latitudes to high latitudes. The TEC anomalies before the volcanic eruptions in low-mid latitudes are within the volcanic affected areas, but do not coincide with the volcanic foci. The corresponding TEC anomalies could be observed in the conjugated region, and all the TEC anomalies in the volcanic affected areas are usually close to bounds of equatorial anomaly zones. However, the TEC anomalies preceding these eruptions in high latitudes usually surround the volcano, and no TEC anomalies appear in the conjugated region. These conclusions have potential applications to the pre- diction of great volcanic eruptions in the future. © 2016 Elsevier B.V. All rights reserved. Keywords: Volcanic eruption TEC anomalies Spatial distribution Occurrence rate Geographical position Equatorial anomaly zone 1. Introduction Ionosphere contains large numbers of free electrons whose genera- tion, migration and neutralization of free electrons lead to the iono- spheric complex physical mechanism. The ionosphere with the fixed periodic variations also contains regional perturbations affected by ex- ternal factors. Ionospheric anomalies have been observed before some geophysical activities, such as great earthquakes, volcanic eruptions, tsunamis etc. (Pulinets and Davidenko, 2014; Occhipinti et al., 2006; Heki and Enomoto, 2013; Li et al., 2016). The seismic-ionospheric effect was first found before the great Alaskan earthquake in 1964 (Leonard and Barnes, 1965). After that the phenomenon was further discussed in many literatures (e.g. Whitcomb et al., 1973; Pulinets, 2004; Liu et al., 2006; Wang et al., 2014; Li et al., 2015). For the volcanic- ionospheric effect, researchers usually focused on the ionospheric anomalies after volcanic eruptions and associated scientific studies. Many experiments confirmed that the electromagnetic field could be influenced by the volcanic eruption (Parrot et al., 1993). Johnston (1989) described the transient variation characteristics of electromag- netic effects in volcanic fields thoroughly, and found that the phenome- non may be caused by the piezomagnetic effect attributed to the change of pressure in the earth's crust. The analysis results of St. Helens volcanic eruption showed that the eruption generated a strong oscillating elec- tric field, and a large scale magnetic disturbance was also observed in 1–2 h after the event. Because of the magnetic gas dynamic effect, trav- elling ionospheric disturbances appeared in volcanic fields (Johnston, 1989). The acoustic gravity wave caused by the volcanic eruption could lead to total electron content (TEC) perturbations, which was usu- ally used to estimate the energy of the volcanic eruption (Kanamori and Mori, 1992; Komjathy et al., 2012). Obvious ionospheric anomalies were observed after Soufrière Hills Volcano eruption with GPS data in Carib- bean region, and the eruption energy was approximately 1.53 × 10 10 J (Dautermann et al., 2009a, 2009b). The volcanic eruption is one of the most serious natural disasters in the world with the enormous and horrible power. For instance, the eruption of Vesuvius volcano destroying the Pompeii city on the 24th of August, 79 CE (Lomax et al., 2001). Volcanic activities are so frequent Journal of Volcanology and Geothermal Research 325 (2016) 98–109 ⁎ Corresponding author. E-mail address: jinyunguo1@126.com (J. Guo). http://dx.doi.org/10.1016/j.jvolgeores.2016.06.017 0377-0273/© 2016 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Journal of Volcanology and Geothermal Research journal homepage: www.elsevier.com/locate/jvolgeores