Ono, Y.; Ida, Y.; Kasahara, Y.; Hobara, Y.; Hayakawa, M.; Rozhnoi, A.; Solovieva, M.; Molchanov, O. A.; Ohta, K. Ionospheric Perturbations Associated With Two Huge Earthquakes in Japan, Using Principal Component Analysis for Multiple Subionospheric VLF/LF Propagation Paths. Ann. Geophys. 2012, 55.