Fig. 3
From: PCA and vTEC climatology at midnight over mid-latitude regions
vTECGNSS over the North American region: a amplitude of the temporal variation, a 1 (the y-axis has to be multiplied by a factor of 10−2), b eigenvector or spatial variation, e 1, c synthesized data for mode 1 (a 1·e T1 ) for red (east) and blue (west) rectangles, d difference between red and blue curves of c, e the amplitude of the temporal variation, a 2 (the y-axis has to be multiplied by a factor of 10−2), f eigenvector or spatial variation, e 2, g synthesized data for mode 2 (a 2·e T2 ) for red (east) and blue (west) rectangles, h difference between red and blue curves of g, i the amplitude of the temporal variation, a 3 (the y-axis has to be multiplied by a factor of 10−2), j eigenvector or spatial variation, e 3, k synthesized data for mode 3 (a 3·e T3 ) for red (east) and blue (west) rectangles, and l difference between red and blue curves of k. Finally, the time-averaged \(\overline{\text{vTEC}}_{{{\text{GNSS}} }} \left( x \right)\) (m), the synthesized data, n \(\overline{\text{vTEC}}^{*}_{\text{GNSS}} \left( t \right)\), for red (east) and blue (west) rectangles, and the difference (\(\overline{\text{dvTEC}}_{{{\text{GNSS}} }}^{*} \left( t \right)\)) between red and blue curves of n (o)