Fig. 8

Results obtained applying MC-NMF to geomagnetic spectrograms from four observatories. a\({\text{BR}}\) at 9/30,720 Hz (left: BMT, left mid: KAK, right mid: KNY, and right: MMB). The uppers show \({\text{BR}}\) of the x component and the lowers show \({\text{BR}}\) of the y component. The vertical axis denotes years during 2000–2009 (the standard is 2000), and the horizontal axis denotes IDs of Basis vectors. b The \({\text{SSE}}\left( {{\text{KAK}},{\text{KNY}}} \right)\) (red), \({\text{SSE}}\left( {{\text{KAK}},{\text{MMB}}} \right)\) (light blue), and \({\text{SSE}}\left( {{\text{KNY}},{\text{MMB}}} \right)\) (orange). The upper denotes the \({\text{SSE}}\) of the x component and the lower denotes the \({\text{SSE}}\) of the y component. The vertical axis denotes \({\text{SSE}}\) and the horizontal axis denotes years