1 Introduction Volcanic eruptions (Dautermann et al., 2009; Hao et al., 2006; Liu et al., 1982; Nakashima et al., 2016; Roberts et al., 1982; Shults et al., 2016), earthquakes and tsunamis are known to trigger acoustic waves that propagate upward, interact with the ionosphere and induce electron density variations, instigating discrete ionospheric disturbances (Afraimovich et al., 2010, 2013; Astafyeva et al., 2014; Calais & Minster, 1995; Catherine et al., 2017; Ducic et al., 2003; Heki &...
