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The air ion density observed at Sendai during a period of 10/02/2013 to 30/04/2016 (more than 3 years) has been analyzed in terms of natural time critical analysis. It is then found that the air ions exhibit criticalities at some specific time periods, as a signature of pre-earthquake (EQ) fracturing process in the lithosphere. So it is likely to conclude that this criticality analysis enables us to associate the criticality in ion density to an EQ as a general tendency. The detection of air ions at a particular place suggests that those ions may be a precursor to an EQ (magnitude greater than 5.0) occurring within a radius of 200 km from the ion observatory. However, based on a comparison with the corresponding VLF/LF sub-ionospheric propagation data, we cannot say anything about a certain relationship of those air ions with the lower ionospheric perturbation as seen by VLF/LF, because the temporal scale of ions is medium-termed, but VLF/LF perturbation is short-termed, which makes it extremely difficult to correlate between the two.

international journal of electronics and applied research

Possible relation of air ion density anomalies with earthquakes and the associated precursory ionospheric perturbations: An analysis in terms of criticality